LM1876 LM1876TF TF15B C1996 RRD-B30M86 2N3904 LM4860 LM4860M C1995 RRD-B30M75 - Datasheet Archive

 

LM1876 Audio Power Amplifier Series Dual 20W Audio Power Amplifier with Mute and Standby Modes General Description Key

 

August 1996 LM1876 LM1876 Audio Power Amplifier Series Dual 20W Audio Power Amplifier with Mute and Standby Modes General Description Key Specifications The LM1876 LM1876 is a stereo audio amplifier capable of delivering typically 20W per channel of continuous average output power into a 4X or 8X load with less than 0 1% (THD a N) Y Each amplifier has an independent smooth transition fadein out mute and a power conserving standby mode which can be controlled by external logic The performance of the LM1876 LM1876 utilizing its Self Peak Instantaneous Temperature ( Ke) (SPiKeTM ) Protection Circuitry places it in a class above discrete and hybrid amplifiers by providing an inherently dynamically protected Safe Operating Area (SOA) SPiKe Protection means that these parts are safeguarded at the output against overvoltage undervoltage overloads including thermal runaway and instantaneous temperature peaks Y Y Features Y Y Y Y Y SPiKe Protection Minimal amount of external components necessary Quiet fade-in out mute mode Standby-mode Isolated 15-lead TO-220 package Applications Y Y Y Typical Application THD a N at 1 kHz at 2 x 15W continuous average output power into 4X or 8X 0 1% (max) THD a N at 1 kHz at continuous average output power of 2 x 20W into 8X 0 009% (typ) Standby current 4 2 mA (typ) High-end stereo TVs Component stereo Compact stereo Connection Diagram Isolated Plastic Package TL H 12072 ­ 2 Top View TL H 12072 ­ 1 Order Number LM1876TF LM1876TF See NS Package Number TF15B TF15B FIGURE 1 Typical Audio Amplifier Application Circuit Note Numbers in parentheses represent pinout for amplifier B Optional component dependent upon specific design requirements SPiKeTM Protection and OvertureTM are trademarks of National Semiconductor Corporation C1996 C1996 National Semiconductor Corporation TL H 12072 RRD-B30M86 RRD-B30M86 Printed in U S A http www national com LM1876 LM1876 Overture Audio Power Amplifier Series Dual 20W Audio Power Amplifier with Mute and Standby Modes PRELIMINARY Absolute Maximum Ratings (Notes 1 and 2) Junction Temperature (Note 5) If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications 150 C Thermal Resistance iJC (Note 11) iJA Supply Voltage lVCCl a lVEEl (No Input) 64V 64V Supply Voltage lVCCl a lVEEl (with Input) Common Mode Input Voltage (VCC or VEE) and lVCCl a lVEEl s 54V Differential Input Voltage 54V Output Current Internally Limited Power Dissipation (Note 3) 62 5W ESD Susceptability (Note 4) 2000V 2C W 43 C W Soldering Information TF Package (10 sec ) 260 C Storage Temperature b 40 C to a 150 C Operating Ratings (Notes 1 and 2) Temperature Range TMIN s TA s TMAX Supply Voltage lVCCl a lVEEl b 20 C s TA s a 85 C 20V to 64V Note Operation is guaranteed up to 64V however distortion may be introduced from SPiKe Protection Circuitry if proper thermal considerations are not taken into account Refer to the Application Information section for a complete explanation Electrical Characteristics (Notes 1 and 2) The following specifications apply for VCC e a 22V VEE e b22V with RL e 8X unless otherwise specified Limits apply for TA e 25 C LM1876 LM1876 Symbol lVCCl a lVEEl PO THD a N Xtalk Parameter Conditions Power Supply Voltage (Note 8) GND b VEE t 9V Output Power (Continuous Average) THD a N e 0 1% (max) f e 1 kHz lVCCl e lVEEl e 22V RL e 8X lVCCl e lVEEl e 20V RL e 4X (Note 10) Typical (Note 6) Total Harmonic Distortion Plus Noise 15 W ch RL e 8X 15 W ch RL e 4X lVCCl e lVEEl e 20V 20 Hz s f s 20 kHz AV e 26 dB Limit (Note 7) Units (Limits) 20 64 20 22 V (min) V (max) 15 15 W ch (min) W ch (min) 0 08 01 % % Channel Separation f e 1 kHz VO e 10 9 Vrms 80 Slew Rate VIN e 1 414 Vrms trise e 2 ns 18 12 V ms (min) Total Quiescent Power Supply Current Both Amplifiers VCM e 0V VO e 0V IO e 0 mA Standby Off Standby On 50 42 80 6 mA (max) mA (max) Input Offset Voltage VCM e 0V IO e 0 mA 20 15 mV (max) IB Input Bias Current VCM e 0V IO e 0 mA 02 05 mA (max) IOS Input Offset Current VCM e 0V IO e 0 mA 0 002 02 mA (max) IO Output Current Limit lVCCl e lVEEl e 10V tON e 10 ms VO e 0V 35 29 A (min) Output Dropout Voltage (Note 9) lVCC ­ VOl lVO ­ VEEl 18 25 23 32 V (max) V (max) SR Itotal VOS VOD DC Electrical Test Refer to Test Circuit http 1 AC Electrical Test Refer to Test Circuit VCC e 20V IO e a 100 mA VEE e b20V IO e b100 mA 2 www national com 2 dB Electrical Characteristics (Notes 1 and 2) The following specifications apply for VCC e a 22V VEE e b22V with RL e 8X unless otherwise specified Limits apply for TA e 25 C (Continued) LM1876 LM1876 Symbol PSRR Parameter Conditions Power Supply Rejection Ratio VCC e 25V to 10V VEE e b25V VCM e 0V IO e 0 mA VCC e 25V VEE e b25V to b10V VCM e 0V IO e 0 mA Units (Limits) Typical (Note 6) Limit (Note 7) 115 85 dB (min) 110 85 dB (min) CMRR Common Mode Rejection Ratio VCC e 35V to 10V VEE e b10V to b35V VCM e 10V to b10V IO e 0 mA 110 80 dB (min) AVOL Open Loop Voltage Gain RL e 2 kX D VO e 20 V 110 90 dB (min) Gain Bandwidth Product fO e 100 kHz VIN e 50 mVrms 75 5 MHz (min) Input Noise IHF A Weighting Filter RIN e 600X (Input Referred) 20 8 mV (max) Signal-to-Noise Ratio PO e 1W A Weighted Measured at 1 kHz RS e 25X PO e 15W A Weighted Measured at 1 kHz RS e 25X GBWP eIN SNR 98 dB 108 dB AM Mute Attenuation Pin 6 11 at 2 5V 115 80 dB (min) Standby Pin VIL VIH Standby Low Input Voltage Standby High Input Voltage Not in Standby Mode In Standby Mode 20 08 25 V (max) V (min) Mute pin VIL VIH Mute Low Input Voltage Mute High Input Voltage Outputs Not Muted Outputs Muted 20 08 25 V (max) V (min) DC Electrical Test Refer to Test Circuit 1 AC Electrical Test Refer to Test Circuit 2 Note 1 All voltages are measured with respect to the GND pins (5 10) unless otherwise specified Note 2 Absolute Maximum Ratings indicate limits beyond which damage to the device may occur Operating Ratings indicate conditions for which the device is functional but do not guarantee specific performance limits Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits This assumes that the device is within the Operating Ratings Specifications are not guaranteed for parameters where no limit is given however the typical value is a good indication of device performance Note 3 For operating at case temperatures above 25 C the device must be derated based on a 150 C maximum junction temperature and a thermal resistance of iJC e 2 C W (junction to case) Refer to the section Determining the Correct Heat Sink in the Application Information section Note 4 Human body model 100 pF discharged through a 1 5 kX resistor Note 5 The operating junction temperature maximum is 150 C however the instantaneous Safe Operating Area temperature is 250 C Note 6 Typicals are measured at 25 C and represent the parametric norm Note 7 Limits are guaranteed to National's AOQL (Average Outgoing Quality Level) Note 8 VEE must have at least b 9V at its pin with reference to ground in order for the under-voltage protection circuitry to be disabled In addition the voltage differential between VCC and VEE must be greater than 14V Note 9 The output dropout voltage VOD is the supply voltage minus the clipping voltage Refer to the Clipping Voltage vs Supply Voltage graph in the Typical Performance Characteristics section Note 10 For a 4X load and with g 20V supplies the LM1876 LM1876 can deliver typically 22W of continuous average output power with less than 0 1% (THD a N) With supplies above g 20V the LM1876 LM1876 cannot deliver more than 22W into a 4X due to current limiting of the output transistors Thus increasing the power supply above g 20V will only increase the internal power dissipation not the possible output power Increased power dissipation will require a larger heat sink as explained in the Application Information section Note 11 Preliminary engineering evaluation of iJC for the TF package has been assessed as 2 C W This is a preliminary engineering number and represents the data to this point Please contact your local National Semiconductor sales representative for more information 3 http www national com Test Circuit 1 (DC Electrical Test Circuit) TL H 12072 ­ 3 Test Circuit 2 (AC Electrical Test Circuit) TL H 12072 ­ 4 http www national com 4 Bridged Amplifier Application Circuit TL H 12072 ­ 5 FIGURE 2 Bridged Amplifier Application Circuit Single Supply Application Circuit TL H 12072 ­ 6 FIGURE 3 Single Supply Amplifier Application Circuit Optional components dependent upon specific design requirements 5 http www national com Auxiliary Amplifier Application Circuit TL H 12072 ­ 7 FIGURE 4 Special Audio Amplifier Application Circuit Equivalent Schematic (excluding active protection circuitry) LM1876 LM1876 (per Amp) TL H 12072 ­ 8 http www national com 6 External Components Description Components Functional Description 1 RB Prevents currents from entering the amplifier's non-inverting input which may be passed through to the load upon power down of the system due to the low input impedance of the circuitry when the undervoltage circuitry is off This phenomenon occurs when the supply voltages are below 1 5V 2 Ri Inverting input resistance to provide AC gain in conjunction with Rf 3 Rf Feedback resistance to provide AC gain in conjunction with Ri 4 Ci 5 CS Feedback capacitor which ensures unity gain at DC Also creates a highpass filter with Ri at fC e 1 (2qRiCi) Provides power supply filtering and bypassing Refer to the Supply Bypassing application section for proper placement and selection of bypass capacitors 6 RV Acts as a volume control by setting the input voltage level 7 RIN Sets the amplifier's input terminals DC bias point when CIN is present in the circuit Also works with CIN to create a highpass filter at fC e 1 (2qRINCIN) Refer to Figure 4 8 CIN Input capacitor which blocks the input signal's DC offsets from being passed onto the amplifier's inputs 9 RSN Works with CSN to stabilize the output stage by creating a pole that reduces high frequency instabilities 10 CSN Works with RSN to stabilize the output stage by creating a pole that reduces high frequency instabilities The pole is set at fC e 1 (2qRSNCSN) Refer to Figure 4 11 12 L R Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce the Q of the series resonant circuit Also provides a low impedance at low frequencies to short out R and pass audio signals to the load Refer to Figure 4 13 RA Provides DC voltage biasing for the transistor Q1 in single supply operation 14 CA Provides bias filtering for single supply operation 15 RINP Limits the voltage difference between the amplifier's inputs for single supply operation Refer to the Clicks and Pops application section for a more detailed explanation of the function of RINP 16 RBI Provides input bias current for single supply operation Refer to the Clicks and Pops application section for a more detailed explanation of the function of RBI 17 RE Establishes a fixed DC current for the transistor Q1 in single supply operation This resistor stabilizes the halfsupply point along with CA Optional components dependent upon specific design requirements 7 http www national com Typical Performance Characteristics THD a N vs Frequency THD a N vs Frequency THD a N vs Frequency THD a N vs Output Power THD a N vs Output Power THD a N vs Output Power THD a N vs Output Power THD a N vs Output Power THD a N vs Output Power Clipping Voltage vs Supply Voltage Clipping Voltage vs Supply Voltage Clipping Voltage vs Supply Voltage TL H 12072 ­ 10 http www national com 8 Typical Performance Characteristics (Continued) Output Power vs Load Resistance Power Dissipation vs Output Power Power Dissipation vs Output Power Output Power vs Supply Voltage Output Mute vs Mute Pin Voltage Output Mute vs Mute Pin Voltage Channel Separation vs Frequency Pulse Response Large Signal Response Power Supply Rejection Ratio Common-Mode Rejection Ratio Open Loop Frequency Response TL H 12072 ­ 11 9 http www national com Typical Performance Characteristics (Continued) Safe Area SPiKe Protection Response Supply Current vs Supply Voltage Pulse Thermal Resistance Pulse Thermal Resistance Supply Current vs Output Voltage Pulse Power Limit Pulse Power Limit Supply Current vs Case Temperature Supply Current (ICC) vs Standby Pin Voltage Supply Current (IEE) vs Standby Pin Voltage Input Bias Current vs Case Temperature TL H 12072 ­ 9 http www national com 10 Application Information the fault condition is temporary but a sustained fault will cause the device to cycle in a Schmitt Trigger fashion between the thermal shutdown temperature limits of 165 C and 155 C This greatly reduces the stress imposed on the IC by thermal cycling which in turn improves its reliability under sustained fault conditions Since the die temperature is directly dependent upon the heat sink used the heat sink should be chosen such that thermal shutdown will not be reached during normal operation Using the best heat sink possible within the cost and space constraints of the system will improve the long-term reliability of any power semiconductor device as discussed in the Determining the Correct Heat Sink Section MUTE MODE By placing a logic-high voltage on the mute pins the signal going into the amplifiers will be muted If the mute pins are left floating or connected to a logic-low voltage the amplifiers will be in a non-muted state There are two mute pins one for each amplifier so that one channel can be muted without muting the other if the application requires such a configuration Refer to the Typical Performance Characteristics section for curves concerning Mute Attenuation vs Mute Pin Voltage STANDBY MODE The standby mode of the LM1876 LM1876 allows the user to drastically reduce power consumption when the amplifiers are idle By placing a logic-high voltage on the standby pins the amplifiers will go into Standby Mode In this mode the current drawn from the VCC supply is typically less than 10 mA total for both amplifiers The current drawn from the VEE supply is typically 4 2 mA Clearly there is a significant reduction in idle power consumption when using the standby mode There are two Standby pins so that one channel can be put in standby mode without putting the other amplifier in standby if the application requires such flexibility Refer to the Typical Performance Characteristics section for curves showing Supply Current vs Standby Pin Voltage for both supplies DETERMlNlNG MAXIMUM POWER DISSIPATION Power dissipation within the integrated circuit package is a very important parameter requiring a thorough understanding if optimum power output is to be obtained An incorrect maximum power dissipation calculation may result in inadequate heat sinking causing thermal shutdown and thus limiting the output power Equation (1) exemplifies the theoretical maximum power dissipation point of each amplifier where VCC is the total supply voltage PDMAX e VCC2 2q2RL (1) Thus by knowing the total supply voltage and rated output load the maximum power dissipation point can be calculated The package dissipation is twice the number which results from equation (1) since there are two amplifiers in each LM1876 LM1876 Refer to the graphs of Power Dissipation versus Output Power in the Typical Performance Characteristics section which show the actual full range of power dissipation not just the maximum theoretical point that results from equation (1) UNDER-VOLTAGE PROTECTION Upon system power-up the under-voltage protection circuitry allows the power supplies and their corresponding capacitors to come up close to their full values before turning on the LM1876 LM1876 such that no DC output spikes occur Upon turn-off the output of the LM1876 LM1876 is brought to ground before the power supplies such that no transients occur at power-down DETERMINING THE CORRECT HEAT SINK The choice of a heat sink for a high-power audio amplifier is made entirely to keep the die temperature at a level such that the thermal protection circuitry does not operate under normal circumstances The thermal resistance from the die (junction) to the outside air (ambient) is a combination of three thermal resistances iJC iCS and iSA In addition the thermal resistance iJC (junction to case) of the LM1876 LM1876 is 2 C W Using Thermalloy Thermacote thermal compound the thermal resistance iCS (case to sink) is about 0 2 C W Since convection heat flow (power dissipation) is analogous to current flow thermal resistance is analogous to electrical resistance and temperature drops are analogous to voltage drops the power dissipation out of the LM1876 LM1876 is equal to the following PDMAX e (TJMAXbTAMB) iJA (2) OVER-VOLTAGE PROTECTION The LM1876 LM1876 contains over-voltage protection circuitry that limits the output current to approximately 3 5 Apk while also providing voltage clamping though not through internal clamping diodes The clamping effect is quite the same however the output transistors are designed to work alternately by sinking large current spikes SPiKe PROTECTION The LM1876 LM1876 is protected from instantaneous peak-temperature stressing of the power transistor array The Safe Operating graph in the Typical Performance Characteristics section shows the area of device operation where SPiKe Protection Circuitry is not enabled The waveform to the right of the SOA graph exemplifies how the dynamic protection will cause waveform distortion when enabled THERMAL PROTECTION The LM1876 LM1876 has a sophisticated thermal protection scheme to prevent long-term thermal stress of the device When the temperature on the die reaches 165 C the LM1876 LM1876 shuts down It starts operating again when the die temperature drops to about 155 C but if the temperature again begins to rise shutdown will occur again at 165 C Therefore the device is allowed to heat up to a relatively high temperature if where TJMAX e 150 C TAMB is the system ambient temperature and iJA e iJC a iCS a iSA Once the maximum package power dissipation has been calculated using equation (1) the maximum thermal resistance iSA (heat sink to ambient) in C W for a heat sink can be calculated This calculation is made using equation (3) which is derived by solving for iSA in equation (2) iSA e (TJMAXbTAMB)bPDMAX(iJC a iCS) PDMAX (3) 11 http www national com Application Information (Continued) Again it must be noted that the value of iSA is dependent upon the system designer's amplifier requirements If the ambient temperature that the audio amplifier is to be working under is higher than 25 C then the thermal resistance for the heat sink given all other things are equal will need to be smaller SINGLE-SUPPLY AMPLIFIER APPLICATION The typical application of the LM1876 LM1876 is a split supply amplifier But as shown in Figure 3 the LM1876 LM1876 can also be used in a single power supply configuration This involves using some external components to create a half-supply bias which is used as the reference for the inputs and outputs Thus the signal will swing around half-supply much like it swings around ground in a split-supply application Along with proper circuit biasing a few other considerations must be accounted for to take advantage of all of the LM1876 LM1876 functions The LM1876 LM1876 possesses a mute and standby function with internal logic gates that are half-supply referenced Thus to enable either the Mute or Standby function the voltage at these pins must be a minimum of 2 5V above half-supply In single-supply systems devices such as microprocessors and simple logic circuits used to control the mute and standby functions are usually referenced to ground not half-supply Thus to use these devices to control the logic circuitry of the LM1876 LM1876 a ``level shifter '' like the one shown in Figure 5 must be employed A level shifter is not needed in a split-supply configuration since ground is also half-supply SUPPLY BYPASSING The LM1876 LM1876 has excellent power supply rejection and does not require a regulated supply However to improve system performance as well as eliminate possible oscillations the LM1876 LM1876 should have its supply leads bypassed with low-inductance capacitors having short leads that are located close to the package terminals Inadequate power supply bypassing will manifest itself by a low frequency oscillation known as ``motorboating'' or by high frequency instabilities These instabilities can be eliminated through multiple bypassing utilizing a large tantalum or electrolytic capacitor (10 mF or larger) which is used to absorb low frequency variations and a small ceramic capacitor (0 1 mF) to prevent any high frequency feedback through the power supply lines If adequate bypassing is not provided the current in the supply leads which is a rectified component of the load current may be fed back into internal circuitry This signal causes distortion at high frequencies requiring that the supplies be bypassed at the package terminals with an electrolytic capacitor of 470 mF or more BRIDGED AMPLIFIER APPLICATION The LM1876 LM1876 has two operational amplifiers internally allowing for a few different amplifier configurations One of these configurations is referred to as ``bridged mode'' and involves driving the load differentially through the LM1876 LM1876's outputs This configuration is shown in Figure 2 Bridged mode operation is different from the classical single-ended amplifier configuration where one side of its load is connected to ground A bridge amplifier design has a distinct advantage over the single-ended configuration as it provides differential drive to the load thus doubling output swing for a specified supply voltage Consequently theoretically four times the output power is possible as compared to a single-ended amplifier under the same conditions This increase in attainable output power assumes that the amplifier is not current limited or clipped A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation For each operational amplifier in a bridge configuration the internal power dissipation will increase by a factor of two over the single ended dissipation Thus for an audio power amplifier such as the LM1876 LM1876 which has two operational amplifiers in one package the package dissipation will increase by a factor of four To calculate the LM1876 LM1876's maximum power dissipation point for a bridged load multiply equation (1) by a factor of four This value of PDMAX can be used to calculate the correct size heat sink for a bridged amplifier application Since the internal dissipation for a given power supply and load is increased by using bridged-mode the heatsink's iSA will have to decrease accordingly as shown by equation (3) Refer to the section Determining the Correct Heat Sink for a more detailed discussion of proper heat sinking for a given application http www national com TL H 12072 ­ 12 FIGURE 5 Level Shift Circuit When the voltage at the Logic Input node is 0V the 2N3904 2N3904 is ``off'' and thus resistor Rc pulls up mute or standby input to the supply This enables the mute or standby function When the Logic Input is 5V the 2N3904 2N3904 is ``on'' and consequently the voltage at the collector is essentially 0V This will disable the mute or standby function and thus the amplifier will be in its normal mode of operation Rshift along with Cshift creates an RC time constant that reduces transients when the mute or standby functions are enabled or disabled Additionally Rshift limits the current supplied by the internal logic gates of the LM1876 LM1876 which insures device reliability Refer to the Mute Mode and Standby Mode sections in the Application Information section for a more detailed description of these functions CLICKS AND POPS In the typical application of the LM1876 LM1876 as a split-supply audio power amplifier the IC exhibits excellent ``click'' and ``pop'' performance when utilizing the mute and standby modes In addition the device employs Under-Voltage Protection which eliminates unwanted power-up and powerdown transients The basis for these functions are a stable and constant half-supply potential In a split-supply application ground is the stable half-supply potential But in a single-supply application the half-supply needs to charge up just like the supply rail VCC This makes the task of attaining a clickless and popless turn-on more challenging Any uneven charging of the amplifier inputs will result in output clicks and pops due to the differential input topology of the LM1876 LM1876 12 Application Information (Continued) For 15W of output power into an 8X load the required VOPEAK is 15 49V A minimum supply rail of 20 5V results from adding VOPEAK and VOD With regulation the maximum supplies are g 26V and the required IOPEAK is 1 94A from equation (5) It should be noted that for a dual 15W amplifier into an 8X load the IOPEAK drawn from the supplies is twice 1 94 Apk or 3 88 Apk At this point it is a good idea to check the Power Output vs Supply Voltage to ensure that the required output power is obtainable from the device while maintaining low THD a N In addition the designer should verify that with the required power supply voltage and load impedance that the required heatsink value iSA is feasible given system cost and size constraints Once the heatsink issues have been addressed the required gain can be determined from Equation (6) AV t 0(PORL) (VIN) e VORMS VINRMS (6) To achieve a transient free power-up and power-down the voltage seen at the input terminals should be ideally the same Such a signal will be common-mode in nature and will be rejected by the LM1876 LM1876 In Figure 3 the resistor RINP serves to keep the inputs at the same potential by limiting the voltage difference possible between the two nodes This should significantly reduce any type of turn-on pop due to an uneven charging of the amplifier inputs This charging is based on a specific application loading and thus the system designer may need to adjust these values for optimal performance As shown in Figure 3 the resistors labeled RBI help bias up the LM1876 LM1876 off the half-supply node at the emitter of the 2N3904 2N3904 But due to the input and output coupling capacitors in the circuit along with the negative feedback there are two different values of RBI namely 10 kX and 200 kX These resistors bring up the inputs at the same rate resulting in a popless turn-on Adjusting these resistors values slightly may reduce pops resulting from power supplies that ramp extremely quick or exhibit overshoot during system turn-on From equation 6 the minimum AV is AV t 11 By selecting a gain of 21 and with a feedback resistor Rf e 20 kX the value of Ri follows from equation (7) Ri e Rf (AV b 1) (7) Thus with Ri e 1 kX a non-inverting gain of 21 will result Since the desired input impedance was 47 kX a value of 47 kX was selected for RIN The final design step is to address the bandwidth requirements which must be stated as a pair of b3 dB frequency points Five times away from a b 3 dB point is 0 17 dB down from passband response which is better than the required g 0 25 dB specified This fact results in a low and high frequency pole of 4 Hz and 100 kHz respectively As stated in the External Components section Ri in conjunction with Ci create a high-pass filter Ci t 1 (2q 1 kX 4 Hz) e 39 8 mF use 39 mF AUDIO POWER AMPLlFIER DESIGN Design a 15W 8X Audio Amplifier Given Power Output 15 Wrms Load Impedance 8X Input Level 1 Vrms(max) Input Impedance 47 kX Bandwidth 20 Hzb20 kHz g 0 25 dB A designer must first determine the power supply requirements in terms of both voltage and current needed to obtain the specified output power VOPEAK can be determined from equation (4) and IOPEAK from equation (5) VOPEAK e 0(2RLPO) (4) IOPEAK e 0(2PO) RL (5) To determine the maximum supply voltage the following conditions must be considered Add the dropout voltage to the peak output swing VOPEAK to get the supply rail at a current of IOPEAK The regulation of the supply determines the unloaded voltage which is usually about 15% higher The supply voltage will also rise 10% during high line conditions Therefore the maximum supply voltage is obtained from the following equation g (VOPEAK a VOD) (1 a regulation) (1 1) Max supplies The high frequency pole is determined by the product of the desired high frequency pole fH and the gain AV With a AV e 21 and fH e 100 kHz the resulting GBWP is 2 1 MHz which is less than the guaranteed minimum GBWP of the LM1876 LM1876 of 5 MHz This will ensure that the high frequency response of the amplifier will be no worse than 0 17 dB down at 20 kHz which is well within the bandwidth requirements of the design 13 http www national com LM1876 LM1876 Overture Audio Power Amplifier Series Dual 20W Audio Power Amplifier with Mute and Standby Modes Physical Dimensions inches (millimeters) unless otherwise noted Isolated TO-220 15-Lead Package Order Number LM1876TF LM1876TF NS Package Number TF15B TF15B LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION As used herein 1 Life support devices or systems are devices or systems which (a) are intended for surgical implant into the body or (b) support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user National Semiconductor Corporation 1111 West Bardin Road Arlington TX 76017 Tel 1(800) 272-9959 Fax 1(800) 737-7018 http www national com 2 A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness National Semiconductor Europe Fax a49 (0) 180-530 85 86 Email europe support nsc com Deutsch Tel a49 (0) 180-530 85 85 English Tel a49 (0) 180-532 78 32 Fran ais Tel a49 (0) 180-532 93 58 Italiano Tel a49 (0) 180-534 16 80 National Semiconductor Hong Kong Ltd 13th Floor Straight Block Ocean Centre 5 Canton Rd Tsimshatsui Kowloon Hong Kong Tel (852) 2737-1600 Fax (852) 2736-9960 National Semiconductor Japan Ltd Tel 81-043-299-2308 Fax 81-043-299-2408 National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications LM4860 LM4860 Boomer Audio Power Amplifier Series 1W Audio Power Amplifier with Shutdown Mode General Description Key Specifications The LM4860 LM4860 is a bridge-connected audio power amplifier capable of delivering 1W of continuous average power to an 8X load with less than 1% (THD a N) over the audio spectrum from a 5V power supply Y Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components using surface mount packaging Since the LM4860 LM4860 does not require output coupling capacitors bootstrap capacitors or snubber networks it is optimally suited for low-power portable systems Features Y Y Y Y Y Y The LM4860 LM4860 features an externally controlled low-power consumption shutdown mode as well as an internal thermal shutdown protection mechanism It also includes two headphone control inputs and a headphone sense output for external monitoring Y Y Y THD a N at 1W continuous average output power into 8X Instantaneous peak output power Shutdown current 1% (max) l 2W 0 6 mA (typ) No output coupling capacitors bootstrap capacitors or snubber circuits are necessary Small Outline (SO) power packaging Compatible with PC power supplies Thermal shutdown protection circuitry Unity-gain stable External gain configuration capability Two headphone control inputs and headphone sensing output Applications The unity-gain stable LM4860 LM4860 can be configured by external gain setting resistors for differential gains of 1 to 10 without the use of external compensation components Y Y Y Y Y Personal computers Portable consumer products Cellular phones Self-powered speakers Toys and games Typical Application Connection Diagram Small Outline Package TL H 11988 ­ 2 Top View Order Number LM4860M LM4860M See NS Package Number M16A TL H 11988 ­ 1 FIGURE 1 Typical Audio Amplifier Application Circuit The Boomer registered trademark is licensed to National Semiconductor for audio integrated circuits by Rockford Corporation Patents pending C1995 C1995 National Semiconductor Corporation TL H 11988 RRD-B30M75 RRD-B30M75 Printed in U S A LM4860 LM4860 1W Audio Power Amplifier with Shutdown Mode March 1995 Absolute Maximum Ratings Soldering Information Small Outline Package Vapor Phase (60 sec ) Infrared (15 sec ) If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications Supply Voltage Storage Temperature 215 C 220 C See AN-450 AN-450 ``Surface Mounting and their Effects on Product Reliability'' for other methods of soldering surface mount devices 6 0V b 65 C to a 150 C Input Voltage Power Dissipation ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) Junction Temperature b 0 3V to VDD a 0 3V Internally limited 3000V 250V 150 C Operating Ratings Temperature Range TMIN s TA s TMAX Supply Voltage b 20 C s TA s a 85 C 2 7V s VDD s 5 5V Electrical Characteristics (Notes 1 2) The following specifications apply for VDD e 5V RL e 8X unless otherwise specified Limits apply for TA e 25 C LM4860 LM4860 Symbol Parameter Conditions Typical (Note 6) VDD Supply Voltage IDD Quiescent Power Supply Current VO e 0V IO e 0A (Note 8) ISD Shutdown Current Vpin2 e VDD (Note 9) 06 VOS Output Offset Voltage VIN e 0V Units (Limits) Limit (Note 7) 27 55 V (min) V (max) 15 0 mA (max) 50 50 0 mV (max) 10 W (min) 70 mA PO Output Power THD a N e 1% (max) f e 1 kHz 1 15 THD a N Total Harmonic Distortion a Noise PO e 1 Wrms 20 Hz s f s 20 kHz 0 72 PSRR Power Supply Rejection Ratio VDD e 4 9V to 5 1V 65 Vod Output Dropout Voltage VIN e 0V to 5V Vod e (Vo1 b Vo2) 06 VIH HP-IN High Input Voltage HP-SENSE e 0V to 4V 25 V VIL HP-IN Low Input Voltage HP-SENSE e 4V to 0V 25 V VOH HP-SENSE High Output Voltage IO e 500 mA 28 25 V (min) VOL HP-SENSE Low Output Voltage IO e b500 mA 02 08 V (max) % dB 10 V (max) Note 1 All voltages are measured with respect to the ground pins unless otherwise specified Note 2 Absolute Maximum Ratings indicate limits beyond which damage to the device may occur Operating Ratings indicate conditions for which the device is functional but do not guarantee specific performance limits Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits This assumes that the device is within the Operating Ratings Specifications are not guaranteed for parameters where no limit is given however the typical value is a good indication of device performance Note 3 The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX iJA and the ambient temperature TA The maximum allowable power dissipation is PDMAX e (TJMAX b TA) iJA or the number given in the Absolute Maximum Ratings whichever is lower For the LM4860 LM4860 TJMAX e a 150 C and the typical junction-to-ambient thermal resistance when board mounted is 100 C W Note 4 Human body model 100 pF discharged through a 1 5 kX resistor Note 5 Machine Model 200 pF­240 pF discharged through all pins Note 6 Typicals are measured at 25 C and represent the parametric norm Note 7 Limits are guaranteed to National's AOQL (Average Outgoing Quality Level) Note 8 The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier Note 9 Shutdown current has a wide distribution For Power Management sensitive designs contact your local National Semiconductor Sales Office 2 High Gain Application Circuit TL H 11988 ­ 3 FIGURE 2 Stereo Amplifier with AVD e 20 Single Ended Application Circuit TL H 11988 ­ 4 FIGURE 3 Single-Ended Amplifier with AV e b1 CS and CB size depend on specific application requirements and constraints Typical values of CS and CB are 0 1 mF Pin 2 6 or 7 should be connected to VDD to disable the amplifier or to GND to enable the amplifier These pins should not be left floating These components create a ``dummy'' load for pin 8 for stability purposes 3 External Components Description (Figures 1 Components 2) Functional Description 1 Ri Inverting input resistance which sets the closed-loop gain in conjunction with Rf This resistor also forms a high pass filter with Ci at fC e 1 (2q Ri Ci) 2 Ci Input coupling capacitor which blocks DC voltage at the amplifier's input terminals Also creates a highpass filter with Ri at fC e 1 (2q Ri Ci) 3 Rf Feedback resistance which sets closed-loop gain in conjunction with Ri 4 CS Supply bypass capacitor which provides power supply filtering Refer to the Application Information section for proper placement and selection of supply bypass capacitor 5 CB Bypass pin capacitor which provides half supply filtering Refer to Application Information section for proper placement and selection of bypass capacitor 6 Cf Used when a differential gain of over 10 is desired Cf in conjunction with Rf creates a low-pass filter which bandwidth limits the amplifier and prevents high frequency oscillation bursts fC e 1 (2q Rf Cf) Optional component dependent upon specific design requirements Refer to the Application Information section for more in formation Typical Performance Characteristics THD a N vs Frequency THD a N vs Frequency THD a N vs Frequency THD a N vs Output Power THD a N vs Output Power THD a N vs Output Power TL H 11988 ­ 5 4 Typical Performance Characteristics (Continued) Supply Current vs Time in Shutdown Mode Supply Current vs Supply Voltage Power Derating Curve LM4860 LM4860 Noise Floor vs Frequency Supply Current Distribution vs Temperature Power Dissipation vs Output Power Output Power vs Load Resistance Output Power vs Supply Voltage Open Loop Frequency Response Power Supply Rejection Ratio TL H 11988 ­ 6 5 Application Information heatsinking From Equation 1 assuming a 5V power supply and an 8X load the maximum power dissipation point is 625 mW The maximum power dissipation point obtained from Equation 1 must not be greater than the power dissipation that results from Equation 2 PDMAX e (TJMAX b TA) iJA (2) BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1 the LM4860 LM4860 has two operational amplifiers internally allowing for a few different amplifier configurations The first amplifier's gain is externally configurable while the second amplifier is internally fixed in a unitygain inverting configuration The closed-loop gain of the first amplifier is set by selecting the ratio of Rf to Ri while the second amplifier's gain is fixed by the two internal 40 kX resistors Figure 1 shows that the output of amplifier one serves as the input to amplifier two which results in both amplifiers producing signals identical in magnitude but out of phase 180 Consequently the differential gain for the IC is Avd e 2 (Rf Ri) For the LM4860 LM4860 surface mount package iJA e 100 C W and TJMAX e 150 C Depending on the ambient temperature TA of the system surroundings Equation 2 can be used to find the maximum internal power dissipation supported by the IC packaging If the result of Equation 1 is greater than that of Equation 2 then either the supply voltage must be decreased or the load impedance increased For the typical application of a 5V power supply with an 8X load the maximum ambient temperature possible without violating the maximum junction temperature is approximately 88 C provided that device operation is around the maximum power dissipation point Power dissipation is a function of output power and thus if typical operation is not around the maximum power dissipation point the ambient temperature can be increased Refer to the Typical Performance Characteristics curves for power dissipation information for lower output powers By driving the load differentially through outputs VO1 and VO2 an amplifier configuration commonly referred to as ``bridged mode'' is established Bridged mode operation is different from the classical single-ended amplifier configuration where one side of its load is connected to ground A bridge amplifier design has a few distinct advantages over the single-ended configuration as it provides differential drive to the load thus doubling output swing for a specified supply voltage Consequently four times the output power is possible as compared to a single-ended amplifier under the same conditions This increase in attainable output power assumes that the amplifier is not current limited or clipped In order to choose an amplifier's closed-loop gain without causing excessive clipping which will damage high frequency transducers used in loudspeaker systems please refer to the Audio Power Amplifier Deslgn section A bridge configuration such as the one used in Boomer Audio Power Amplifiers also creates a second advantage over single-ended amplifiers Since the differential outputs VO1 and VO2 are biased at half-supply no net DC voltage exists across the load This eliminates the need for an output coupling capacitor which is required in a single supply single-ended amplifier configuration Without an output coupling capacitor in a single supply single-ended amplifier the half-supply bias across the load would result in both increased internal IC power dissipation and also permanent loudspeaker damage An output coupling capacitor forms a high pass filter with the load requiring that a large value such as 470 mF be used with an 8X load to preserve low frequency response This combination does not produce a flat response down to 20 Hz but does offer a compromise between printed circuit board size and system cost versus low frequency response POWER SUPPLY BYPASSING As with any power amplifier proper supply bypassing is critical for low noise performance and high power supply rejection The capacitor location on both the bypass and power supply pins should be as close to the device as possible As displayed in the Typical Performance CharacterIstIcs section the effect of a larger half-supply bypass capacitor is improved low frequency THD a N due to increased half-supply stability Typical applications employ a 5V regulator with 10 mF and a 0 1 mF bypass capacitors which aid in supply stability but do not eliminate the need for bypassing the supply nodes of the LM4860 LM4860 The selection of bypass capacitors especially CB is thus dependant upon desired low frequency THD a N system cost and size constraints SHUTDOWN FUNCTION In order to reduce power consumption while not in use the LM4860 LM4860 contains a shutdown pin to externally turn off the amplifier's bias circuitry The shutdown feature turns the amplifier off when a logic high is placed on the shutdown pin Upon going into shutdown the output is immediately disconnected from the speaker There is a built-in threshold which produces a drop in quiescent current to 500 mA typically For a 5V power supply this threshold occurs when 2V ­ 3V is applied to the shutdown pin A typical quiescent current of 0 6 mA results when the supply voltage is applied to the shutdown pin In many applications a microcontroller or microprocessor output is used to control the shutdown circuitry which provides a quick smooth transition into shutdown Another solution is to use a single-pole single-throw switch that when closed is connected to ground and enables the amplifier If the switch is open then a soft pull-up resistor of 47 kX will disable the LM4860 LM4860 There are no soft pull-down resistors inside the LM4860 LM4860 so a definite shutdown pin voltage must be appliied externally or the internal logic gate will be left floating which could disable the amplifier unexpectedly POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifier whether the amplifier is bridged or singleended A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation Equation 1 states the maximum power dissipation point for a bridge amplifier operating at a given supply voltage and driving a specified output load PDMAX e 4 (VDD)2 (2q2RL) (1) Since the LM4860 LM4860 has two operational amplifiers in one package the maximum internal power dissipation is 4 times that of a single-ended amplifier Even with this substantial increase in power dissipation the LM4860 LM4860 does not require 6 Application Information (Continued) When a set of headphones are plugged into the system the contact pin of the headphone jack is disconnected from the signal pin interrupting the voltage divider set up by resistors R1 and R2 Resistor R1 then pulls up the HP-IN1 pin enabling the headphone function and disabling the LM4860 LM4860 amplifier The headphone amplifier then drives the headphones whose impedance is in parallel with resistor R2 Since the typical impedance of headphones are 32X resistor R2 has negligible effect on the output drive capability Also shown in Figure 5 are the electrical connections for the headphone jack and plug A 3-wire plug consists of a Tip Ring and Sleave where the Tip and Ring are signal carrying conductors and the Sleave is the common ground return One control pin contact for each headphone jack is sufficient to indicate to control inputs that the user has inserted a plug into a jack and that another mode of operation is desired For a system implementation where the headphone amplifier is designed using a split supply the output coupling cap CC and resistor R2 of Figure 5 can be eliminated The functionality described earlier remains the same however In addition the HP-SENSE pin although it may be connected to the SHUTDOWN pin as shown in Figure 4 may still be used as a control flag It is capable of driving the input to another logic gate or approximately 2 mA without serious loading HEADPHONE CONTROL INPUTS The LM4860 LM4860 possesses two headphone control inputs that disable the amplifier and reduce IDD to less than 1 mA when either one or both of these inputs have a logic-high voltage placed on their pins Unlike the shutdown function the headphone control function does not provide the level of current conservation that is required for battery powered systems Since the quiescent current resulting from the headphone control function is 1000 times more than the shutdown function the residual currents in the device may create a pop at the output when coming out of the headphone control mode The pop effect may be eliminated by connecting the headphone sensing output to the shutdown pin input as shown in Figure 4 This solution will not only eliminate the output pop but will also utilize the full current conservation of the shutdown function by reducing IDD to 0 6 mA The amplifier will then be fully shutdown This configuration also allows the designer to use the control inputs as either two headphone control pins or a headphone control pin and a shutdown pin where the lowest level of current consumption is obtained from either function Figure 5 shows the implementation of the LM4860 LM4860's headphone control function using a single-supply headphone amplifier The voltage divider of R1 and R2 sets the voltage at the HP-IN1 pin to be approximately 50 mV when there are no headphones plugged into the system This logic-low voltage at the HP-IN1 pin enables the LM4860 LM4860 to amplify AC signals Resistor R3 limits the amount of current flowing out of the HP-IN1 pin when the voltage at that pin goes below ground resulting from the music coming from the headphone amplifier The output coupling cap protects the headphones by blocking the amplifier's half-supply DC voltage The capacitor also protects the headphone amplifier from the low voltage set up by resistors R1 and R2 when there aren't any headphones plugged into the system The tricky point to this setup is that the AC output voltage of the headphone amplifier cannot exceed the 2 0V HP-IN1 voltage threshold when there aren't any headphones plugged into the system assuming that R1 and R2 are 100k and 1k respectively The LM4860 LM4860 may not be fully shutdown when this level is exceeded momentarily due to the discharging time constant of the bias-pin voltage This time constant is established by the two 50k resistors (in parallel) with the series bypass capacitor value TL H 11988 ­ 7 FIGURE 4 HP-SENSE Pin to SHUTDOWN Pin Connection 7 Application Information (Continued) TL H 11988 ­ 8 FIGURE 5 Typical Headphone Control Input Circuitry 8 Application Information (Continued) through a 0 1 mF capacitor to a 2 kX load to prevent instability While such an instability will not affect the waveform of VO1 it is good design practice to load the second output HIGHER GAIN AUDIO AMPLIFIER The LM4860 LM4860 is unity-gain stable and requires no external components besides gain-setting resistors an input coupling capacitor and proper supply bypassing in the typical application However if a closed-loop differential gain of greater than 10 is required then a feedback capacitor is needed as shown in Figure 2 to bandwidth limit the amplifier The feedback capacitor creates a low pass filter that eliminates unwanted high frequency oscillations Care should be taken when calculating the b3 dB frequency in that an incorrect combination of Rf and Cf will cause rolloff before 20 kHz A typical combination of feedback resistor and capacitor that will not produce audio band high frequency rolloff is Rf e 100 kX and Cf e 5 pF These components result in a b3 dB point of approximately 320 kHz Once the differential gain of the amplifier has been calculated a choice of Rf will result and Cf can then be calculated from the formula stated in the External Components Description section AUDIO POWER AMPLIFIER DESIGN Design a 500 mW 8X Audio Amplifier Given Power Output 500 mWrms Load Impedance 8X Input Level 1 Vrms(max) Input Impedance 20 kX Bandwidth 20 Hz-20 kHz g 0 25 dB A designer must first determine the needed supply rail to obtain the specified output power Calculating the required supply rail involves knowing two parameters Vopeak and also the dropout voltage The latter is typically 0 7V Vopeak can be determined from equation 3 (3) Vopeak e 0(2 RL PO) For 500 mW of output power into an 8X load the required Vopeak is 2 83V A minimum supply rail of 3 53V results from adding Vopeak and Vod But 3 53V is not a standard voltage that exists in many applications and for this reason a supply rail of 5V is designated Extra supply voltage creates dynamic headroom that allows the LM4860 LM4860 to reproduce peaks in excess of 500 mW without clipping the signal At this time the designer must make sure that the power supply choice along with the output impedance does not violate the conditions explained in the Power Dissipation section Once the power dissipation equations have been addressed the required differential gain can be determined from Equation 4 Avd t 2 0(PO RL) (VIN) e Vorms Vinrms (4) VOICE-BAND AUDIO AMPLIFIER Many applications such as telephony only require a voiceband frequency response Such an application usually requires a flat frequency response from 300 Hz to 3 5 kHz By adjusting the component values of Figure 2 this common application requirement can be implemented The combination of Ri and Ci form a highpass filter while Rf and Cf form a lowpass filter Using the typical voice-band frequency range with a passband differential gain of approximately 100 the following values of Ri Ci Rf and Cf follow from the equations stated in the External Components Description section Ri e 10 kX Rf e 510k Ci e 0 22 mF and Cf e 15 pF Five times away from a b3 dB point is 0 17 dB down from the flatband response With this selection of components the resulting b3 dB points fL and fH are 72 Hz and 20 kHz respectively resulting in a flatband frequency response of better than g 0 25 dB with a rolloff of 6 dB octave outside of the passband If a steeper rolloff is required other common bandpass filtering techniques can be used to achieve higher order filters Rf Rj e Avd 2 (5) From equation 4 the minimum Avd is Avd e 2 Since the desired input impedance was 20 kX and with an Avd of 2 a ratio of 1 1 of Rf to Ri results in an allocation of Ri e Rf e 20 kX Since the Avd was less than 10 a feedback capacitor is not needed The final design step is to address the bandwidth requirements which must be stated as a pair of b3 dB frequency points Five times away from a b 3 dB point is 0 17 dB down from passband response which is better than the required g 0 25 dB specified This fact results in a low and high frequency pole of 4 Hz and 100 kHz respectively As stated in the External Components section Ri in conjunction with Ci create a highpass filter Ci t 1 (2q 20 kX 4 Hz) e 1 98 mF use 2 2 mF SINGLE-ENDED AUDIO AMPLIFIER Although the typical application for the LM4860 LM4860 is a bridged monoaural amp it can also be used to drive a load singleendedly in applications such as PC cards which require that one side of the load is tied to ground Figure 3 shows a common single-ended application where VO1 is used to drive the speaker This output is coupled through a 470 mF capacitor which blocks the half-supply DC bias that exists in all single-supply amplifier configurations This capacitor designated CO in Figure 3 in conjunction with RL forms a highpass filter The b3 dB point of this highpass filter is 1 (2qRLCO) so care should be taken to make sure that the product of RL and CO is large enough to pass low frequencies to the load When driving an 8X load and if a full audio spectrum reproduction is required CO should be at least 470 mF VO2 the output that is not used is connected The high frequency pole is determined by the product of the desired high frequency pole fH and the differential gain Avd With a Avd e 2 and fH e 100 kHz the resulting GBWP e 100 kHz which is much smaller than the LM4860 LM4860 GBWP of 7 MHz This figure displays that if a designer has a need to design an amplifier with a higher differential gain the LM4860 LM4860 can still be used without running into bandwidth problems 9 LM4860 LM4860 1W Audio Power Amplifier with Shutdown Mode Physical Dimensions inches (millimeters) Small Outline Package (M) Order Number LM4860M LM4860M NS Package Number M16A LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION As used herein 1 Life support devices or systems are devices or systems which (a) are intended for surgical implant into the body or (b) support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user National Semiconductor Corporation 2900 Semiconductor Drive P O Box 58090 Santa Clara CA 95052-8090 Tel 1(800) 272-9959 TWX (910) 339-9240 National Semiconductor GmbH Livry-Gargan-Str 10 D-82256 D-82256 F4urstenfeldbruck Germany Tel (81-41) 35-0 Telex 527649 Fax (81-41) 35-1 National Semiconductor Japan Ltd Sumitomo Chemical Engineering Center Bldg 7F 1-7-1 Nakase Mihama-Ku Chiba-City Ciba Prefecture 261 Tel (043) 299-2300 Fax (043) 299-2500 2 A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness National Semiconductor Hong Kong Ltd 13th Floor Straight Block Ocean Centre 5 Canton Rd Tsimshatsui Kowloon Hong Kong Tel (852) 2737-1600 Fax (852) 2736-9960 National Semiconductores Do Brazil Ltda Rue Deputado Lacorda Franco 120-3A Sao Paulo-SP Brazil 05418-000 Tel (55-11) 212-5066 Telex 391-1131931 NSBR BR Fax (55-11) 212-1181 National Semiconductor (Australia) Pty Ltd Building 16 Business Park Drive Monash Business Park Nottinghill Melbourne Victoria 3168 Australia Tel (3) 558-9999 Fax (3) 558-9998 National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications LM4880 LM4880 Boomer Audio Power Amplifier Series Dual 250 mW Audio Power Amplifier with Shutdown Mode General Description Key Specifications The LM4880 LM4880 is a dual audio power amplifier capable of delivering typically 250 mW per channel of continuous average power to an 8X load with 0 1% (THD) using a 5V power supply Y Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components using surface mount packaging Y Since the LM4880 LM4880 does not require bootstrap capacitors or snubber networks it is optimally suited for low-power portable systems Features The LM4880 LM4880 features an externally controlled low-power consumption shutdown mode as well as an internal thermal shutdown protection mechanism The unity-gain stable LM4880 LM4880 can be configured by external gain-setting resistors Y Y Y Y Y Y THD at 1 kHz at 200 mW continuous average output power into 8X 0 1% (max) THD at 1 kHz at 85 mW continuous average output power into 32X 0 1% (typ) Output power at 10% THD a N at 1 kHz into 8X 325 mW (typ) Shutdown Current 0 7 mA (typ) No bootstrap capacitors or snubber circuits are necessary Small Outline (SO) and DIP packaging Unity-gain stable External gain configuration capability Applications Y Y Y Headphone Amplifier Personal Computers CD-ROM Players Typical Application Connection Diagram Small Outline and DIP Packages TL H 12343 ­ 2 Top View Order Number LM4880M LM4880M or LM4880N LM4880N See NS Package Number M08A for SO or NS Package Number N08E for DIP TL H 12343 ­ 1 FIGURE 1 Typical Audio Amplifier Application Circuit Refer to the Application Information section for information concerning proper selection of the input and output coupling capacitors Boomer is a registered trademark of National Semiconductor Corporation C1995 C1995 National Semiconductor Corporation TL H 12343 RRD-B30M125 RRD-B30M125 Printed in U S A LM4880 LM4880 Dual 250 mW Audio Power Amplifier with Shutdown Mode November 1995 Absolute Maximum Ratings If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications See AN-450 AN-450 ``Surface Mounting and their Effects on Product Reliability'' for other methods of soldering surface mount devices Supply Voltage Storage Temperature Thermal Resistance iJC (DIP) iJA (DIP) iJC (SO) iJA (SO) Input Voltage Power Dissipation (Note 3) ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) Junction Temperature Soldering Information Small Outline Package Vapor Phase (60 sec ) Infrared (15 sec ) 6 0V b 65 C to a 150 C b 0 3V to VDD a 0 3V Electrical Characteristics Internally limited 3500V 250V 150 C 37 107 35 170 C C C C W W W W Operating Ratings Temperature Range TMINsTAsTMAX Supply Voltage b 40 C s TA s a 85 C 2 7VsVDDs5 5V 215 C 220 C (Notes 1 2) The following specifications apply for VDD e 5V unless otherwise specified Limits apply for TA e 25 C LM4880 LM4880 Symbol Parameter Conditions Typical (Note 6) Limit (Note 7) Units (Limits) VDD Supply Voltage 27 55 IDD Quiescent Power Supply Current VIN e 0V IO e 0A 36 ISD Shutdown Current VPIN5 e VDD 07 5 mA (max) VOS Output Offset Voltage VIN e 0V 5 50 mV (max) PO Output Power THD e 0 1% (max) f e 1 kHz RL e 8X RL e 32X THD a N e 10% f e 1 kHz RL e 8X RL e 32X 250 85 200 mW (min) mW THD a N Total Harmonic Distortion a Noise RL e 8X PO e 200 mW RL e 32X PO e 75 mW f e 1 kHz PSRR Power Supply Rejection Ratio CB e 1 0 mF VRIPPLE e 200 mVrms f e 100 Hz V (min) V (max) 60 mA (max) 325 110 mW mW 0 03 0 02 % % 50 dB Note 1 All voltages are measured with respect to the ground pin unless otherwise specified Note 2 Absolute Maximum Ratings indicate limits beyond which damage may occur Operating Ratings indicate conditions for which the device is functional but do not guarantee specific performance limits Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits This assumes that the device is within the Operating Ratings Specifications are not guaranteed for parameters where no limit is given however the typical value is a good indication of device performance Note 3 The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX iJA and the ambient temperature TA The maximum allowable power dissipation is PDMAX e (TJMAX b TA) iJA or the number given in the Absolute Maximum Ratings whichever is lower For the LM4880 LM4880 TJMAX e 150 C and the typical junction-to-ambient thermal resistance is 170 C W for package M08A and 107 C W for package N08E Note 4 Human body model 100 pF discharged through a 1 5 kX resistor Note 5 Machine model 220 pF­240 pF discharged through all pins Note 6 Typicals are measured at 25 C and represent the parametric norm Note 7 Limits are guaranteed to National's AOQL (Average Outgoing Quality Level) 2 Automatic Shutdown Circuit TL H 12343 ­ 3 FIGURE 2 Automatic Shutdown Circuit Automatic Switching Circuit TL H 12343 ­ 4 FIGURE 3 Automatic Switching Circuit 3 External Components Description (Figure 1) Components Functional Description 1 Ri Inverting input resistance which sets the closed-loop gain in conjunction with RF This resistor also forms a high pass filter with Ci at fc e 1 (2qRiCi) 2 Ci Input coupling capacitor which blocks the DC voltage at the amplifier's input terminals Also creates a high pass filter with Ri at fc e 1 (2qRiCi) Refer to the section Proper Selection of External Components for an explanation of how to determine the value of Ci 3 RF Feedback resistance which sets closed-loop gain in conjunction with Ri 4 CS Supply bypass capacitor which provides power supply filtering Refer to the Application Information section for proper placement and selection of the supply bypass capacitor 5 CB Bypass pin capacitor which provides half-supply filtering Refer to the section Proper Selection of External Components for information concerning proper placement and selection of CB 6 Co Output coupling capacitor which blocks the DC voltage at the amplifier's output Forms a high pass filter with RL at fo e 1 (2qRLCo) Typical Performance Characteristics THD a N vs Output Power THD a N vs Output Power TL H 12343­5 THD a N vs Output Power TL H 12343 ­ 6 THD a N vs Output Power TL H 12343­8 TL H 12343 ­ 9 4 THD a N vs Output Power TL H 12343 ­ 7 THD a N vs Output Power TL H 12343 ­ 10 Typical Performance Characteristics (Continued) THD a N vs Frequency THD a N vs Frequency TL H 12343­11 THD a N vs Frequency TL H 12343 ­ 12 Output Power vs Load Resistance TL H 12343­14 Output Power vs Supply Voltage TL H 12343 ­ 15 Output Power vs Supply Voltage TL H 12343­17 Clipping Voltage vs Supply Voltage TL H 12343 ­ 18 Clipping Voltage vs Supply Voltage TL H 12343­20 TL H 12343 ­ 21 5 THD a N vs Frequency TL H 12343 ­ 13 Output Power vs Load Resistance TL H 12343 ­ 16 Output Power vs Supply Voltage TL H 12343 ­ 19 Power Dissipation vs Output Power TL H 12343 ­ 22 Typical Performance Characteristics (Continued) Channel Separation Output Attenuation in Shutdown Mode TL H 12343­23 Power Supply Rejection Ratio TL H 12343 ­ 24 Open Loop Frequency Response TL H 12343­26 Frequency Response vs Output Capacitor Size TL H 12343 ­ 27 Frequency Response vs Output Capacitor Size TL H 12343­29 Typical Application Frequency Response TL H 12343 ­ 30 Typical Application Frequency Response TL H 12343­32 TL H 12343 ­ 33 6 Noise Floor TL H 12343 ­ 25 Supply Current vs Supply Voltage TL H 12343 ­ 28 Frequency Response vs Input Capacitor Size TL H 12343 ­ 31 Power Derating Curve TL H 12343 ­ 34 Application Information SHUTDOWN FUNCTION POWER SUPPLY BYPASSING In order to reduce power consumption while not in use the LM4880 LM4880 contains a shutdown pin to externally turn off the amplifier's bias circuitry This shutdown feature turns the amplifier off when a logic high is placed on the shutdown pin The trigger point between a logic low and logic high level is typically half supply It is best to switch between ground and the supply to provide maximum device performance By switching the shutdown pin to VDD the LM4880 LM4880 supply current draw will be minimized in idle mode While the device will be disabled with shutdown pin voltages less than VDD the idle current may be greater than the typical value of 0 7 mA In either case the shutdown pin should be tied to a definite voltage because leaving the pin floating may result in an unwanted shutdown condition In many applications a microcontroller or microprocessor output is used to control the shutdown circuitry which provides a quick smooth transition into shutdown Another solution is to use a single-pole single-throw switch in conjunction with an external pull-up resistor When the switch is closed the shutdown pin is connected to ground and enables the amplifier If the switch is open then the external pull-up resistor will disable the LM4880 LM4880 This scheme guarantees that the shutdown pin will not float which will prevent unwanted state changes As with any power amplifier proper supply bypassing is critical for low noise performance and high power supply rejection The capacitor location on both the bypass and power supply pins should be as close to the device as possible As displayed in the Typical Performance Characteristics section the effect of a larger half supply bypass capacitor is improved low frequency PSRR due to increased half-supply stability Typical applications employ a 5V regulator with 10 mF and a 0 1 mF bypass capacitors which aid in supply stability but do not eliminate the need for bypassing the supply nodes of the LM4880 LM4880 The selection of bypass capacitors especially CB is thus dependant upon desired low frequency PSRR click and pop performance as explained in the section Proper Selection of External Components section system cost and size constraints AUTOMATIC SHUTDOWN CIRCUIT As shown in Figure 2 the LM4880 LM4880 can be set up to automatically shutdown when a load is not connected This circuit is based upon a single control pin common in many headphone jacks This control pin forms a normally closed switch with one of the output pins The output of this circuit (the voltage on pin 5 of the LM4880 LM4880) has two states based on the state of the switch When the switch is open signifying that headphones are inserted the LM4880 LM4880 should be enabled When the switch is closed the LM4880 LM4880 should be off to minimize power consumption The operation of this circuit is rather simple With the switch closed Rp and Ro form a resistor divider which produces a gate voltage of less than 5 mV This gate voltage keeps the NMOS inverter off and Rsd pulls the shutdown pin of the LM4880 LM4880 to the supply voltage This places the LM4880 LM4880 in shutdown mode which reduces the supply current to 0 7 mA typically When the switch is open the opposite condition is produced Resistor Rp pulls the gate of the NMOS high which turns on the inverter and produces a logic low signal on the shutdown pin of the LM4880 LM4880 This state enables the LM4880 LM4880 and places the amplifier in its normal mode of operation This type of circuit is clearly valuable in portable products where battery life is critical but is also benefical for power conscious designs such as ``Green PC's'' POWER DISSIPATION Power dissipation is a major concern when using any power amplifier and must be thoroughly understood to ensure a successful design Equation 1 states the maximum power dissipation point for a single-ended amplifier operating at a given supply voltage and driving a specified output load PDMAX e (VDD)2 (2q2RL) (1) Since the LM4880 LM4880 has two operational amplifiers in one package the maximum internal power dissipation point is twice that of the number which results from Equation 1 Even with the large internal power dissipation the LM4880 LM4880 does not require heat sinking over a large range of ambient temperatures From Equation 1 assuming a 5V power supply and an 8X load the maximum power dissipation point is 158 mW per amplifier Thus the maximum package dissipation point is 317 mW The maximum power dissipation point obtained must not be greater than the power dissipation that results from Equation 2 PDMAX e (TJMAX-TA) iJA (2) AUTOMATIC SWITCHING CIRCUIT A circuit closely related to the Automatic Shutdown Circuit is the Automatic Switching Circuit of Figure 3 The Automatic Switching Circuit utilizes both the input and output of the NMOS inverter to toggle the states of two different audio power amplifiers The LM4880 LM4880 is used to drive stereo single ended loads while the LM4861 LM4861 drives bridged internal speakers In this application the LM4880 LM4880 and LM4861 LM4861 are never on at the same time When the switch inside the headphone jack is open the LM4880 LM4880 is enabled and the LM4861 LM4861 is disabled since the NMOS inverter is on If a headphone jack is not present it is assumed that the internal speakers should be on and thus the voltage on the LM4861 LM4861 shutdown pin is low and the voltage at the LM4880 LM4880 pin is high This results in the LM4880 LM4880 being shutdown and the LM4861 LM4861 being enabled Only one channel of this circuit is shown in Figure 3 to keep the drawing simple but the typical application would a For the LM4880 LM4880 surface mount package iJA e 170 C W and TJMAX e 150 C Depending on the ambient temperature TA of the system surroundings Equation 2 can be used to find the maximum internal power dissipation supported by the IC packaging If the result of Equation 1 is greater than that of Equation 2 then either the supply voltage must be decreased the load impedance increased or the ambient temperature reduced For the typical application of a 5V power supply with an 8X load the maximum ambient temperature possible without violating the maximum junction temperature is approximately 96 C provided that device operation is around the maximum power dissipation point Power dissipation is a function of output power and thus if typical operation is not around the maximum power dissipation point the ambient temperature may be increased accordingly Refer to the Typical Performance Characteristics curves for power dissipation information for lower output powers 7 Application Information (Continued) LM4880 LM4880 driving a stereo external headphone jack and two LM4861 LM4861's driving the internal stereo speakers If only one internal speaker is required a single LM4861 LM4861 can be used as a summer to mix the left and right inputs into a single mono channel AUDIO POWER AMPLIFIER DESIGN Design a Dual 200 mW 8X Audio Amplifier Given Power Output 200 mWrms Load Impedance 8X Input Level 1 Vrms (max) Input Impedance 20 kX Bandwidth 100 Hz ­ 20 kHz g 0 50 dB PROPER SELECTION OF EXTERNAL COMPONENTS Selection of external components when using integrated power amplifiers is critical to optimize device and system performance While the LM4880 LM4880 is tolerant of external component combinations care must be exercised when choosing component values The LM4880 LM4880 is unity-gain stable which gives a designer maximum system flexibility The LM4880 LM4880 should be used in low gain configurations to minimize THD a N values and maximize the signal to noise ratio Low gain configurations require large input signals to obtain a given output power Input signals equal to or greater than 1 Vrms are available from sources such as audio codecs Please refer to the section Audio Power Amplifier Design for a more complete explanation of proper gain selection Besides gain one of the major design considerations is the closed-loop bandwidth of the amplifier To a large extent the bandwidth is dictated by the choice of external components shown in Figure 1 Both the input coupling capacitor Ci and the output coupling capacitor Co form first order high pass filters which limit low frequency response These values should be chosen based on needed frequency response for a few distinct reasons A designer must first determine the needed supply rail to obtain the specified output power Calculating the required supply rail involves knowing two parameters Vopeak and also the dropout voltage As shown in the Typical Performance Curves the dropout voltage is typically 0 5V Vopeak can be determined from Equation 3 Vopeak e 0(2RLPo) For 200 mW of output power into an 8X load the required Vopeak is 1 79V Since this is a single supply application the minimum supply voltage is twice the sum of Vopeak and Vod Since 5V is a standard supply voltage in most applications it is chosen for the supply rail Extra supply voltage creates headroom that allows the LM4880 LM4880 to reproduce peaks in excess of 200 mW without clipping the signal At this time the designer must make sure that the power supply choice along with the output impedance does not violate the conditions explained in the Power Dissipation section Remember that the maximum power dissipation value from Equation 1 must be multiplied by two since there are two independent amplifiers inside the package Once the power dissipation equations have been addressed the required gain can be determined from Equation 4 (4) lAVl t 0(PoRL) (VIN) e Vorms Vinrms Selection of Input and Output Capacitor Size Large input and output capacitors are both expensive and space hungry for portable designs Clearly a certain sized capacitor is needed to couple in low frequencies without severe attenuation But in many cases the transducers used in portable systems whether internal or external have little ability to reproduce signals below 100 Hz­150 Hz Thus using large input and output capacitors may not increase system performance In addition to system cost and size click and pop performance is effected by the size of the input coupling capacitor Ci A larger input coupling capacitor requires more charge to reach its quiescent DC voltage (normally 1 2 VDD ) This charge comes from the output via the feedback and is apt to create pops upon device enable Thus by minimizing the capacitor size based on necessary low frequency response turn-on pops can be minimized Besides minimizing the input and output capacitor sizes careful consideration should be paid to the bypass capacitor size The bypass capacitor CB is the most critical component to minimize turn-on pops since it determines how fast the LM4880 LM4880 turns on The slower the LM4880 LM4880's outputs ramp to their quiescent DC voltage (nominally 1 2 VDD) the smaller the turn-on pop Choosing CB equal to 1 0 mF along with a small value of Ci (in the range of 0 1 mF to 0 39 mF) should produce a virtually clickless and popless shutdown function While the device will function properly (no oscillations or motorboating) with CB equal to 0 1 mF the device will be much more susceptible to turn-on clicks and pops Thus a value of CB equal to 1 0 mF or larger is recommended in all but the most cost sensitive designs AV e bRF Ri (5) From Equation 4 the minimum gain is AV e b1 26 Since the desired input impedance was 20 kX and with a gain of b1 26 a value of 27 kX is designated for Rf assuming 5% tolerance resistors This combination results in a nominal gain of b1 35 The final design step is to address the bandwidth requirements which must be stated as a pair of b3 dB frequency points Five times away from a b3 dB point is 0 17 dB down from passband response assuming a single pole roll-off As stated in the External Components section both Ri in conjunction with Ci and Co with RL create first order high pass filters Thus to obtain the desired frequency low response of 100 Hz within g 0 5 dB both poles must be taken into consideration The combination of two single order filters at the same frequency forms a second order response This results in a signal which is down 0 34 dB at five times away from the single order filter b3 dB point Thus a frequency of 20 Hz is used in the following equations to ensure that the response if better than 0 5 dB down at 100 Hz Ci t 1 (2q 20kX 20Hz) e 0 397 mF use 0 39 mF Co t 1 (2q 8X 20Hz) e 995 mF use 1000 mF The high frequency pole is determined by the product of the desired high frequency pole fH and the closed-loop gain AV With a closed-loop gain magnitude of 1 35 and fH e 100 kHz the resulting GBWP e 135 kHz which is much smaller than the LM4880 LM4880 GBWP of 12 5 MHz This figure displays that if a designer has a need top design an amplifier with a higher gain the LM4880 LM4880 can still be used without running into bandwidth limitations 8 Physical Dimensions inches (millimeters) 8-Lead (0 150 Wide) Molded Small Outline Package JEDEC Order Number LM4880M LM4880M NS Package Number M08A 9 LM4880 LM4880 Dual 250 mW Audio Power Amplifier with Shutdown Mode Physical Dimensions inches (millimeters) (Continued) 8-Lead (0 300 Wide) Molded Dual-In-Line Package Order Number LM4880N LM4880N NS 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