LM4962 LM4951 AN-1441 AN201788 TLA2011A TLA09ZZA MBR0520 1/10W CSP-9-111C2

Application Note 1441 Nisha Patel April 2006 Introduction 15Vpp (typ) BTL, per channel, to a 2µF+30 load with less than 1%

National Semiconductor Application Note 1441 Nisha Patel April 2006 Introduction 15Vpp (typ) BTL, per channel, to a 2µF+30 load with less than 1% THD+N from a 3.2VDC power supply. The LM4962 LM4962 features a low power consumption shutdown mode, an internal thermal shutdown protection mechanism, over current protection (OCP) and over voltage protection (OVP). The LM4962 LM4962 Evaluation Board is designed to evaluate both mono and stereo applications. The LM4962 LM4962 integrates a switching boost converter with an audio power amplifier. For stereo applications an external audio amplifier is needed. The LM4962 LM4962 Evaluation Board presents the LM4962 LM4962 along with the LM4951 LM4951 audio power amplifier. For more information on the LM4962 LM4962 or LM4951 LM4951 refer to the corresponding datasheet. General Description The LM4962 LM4962 is an audio power amplifier primarily designed for driving ceramic speaker in cell phones, Smart Phones, PDA's and other portable applications. It is capable of driving Operating Conditions · Temperature Range -40°C TA +85°C · Boost Converter Supply Voltage (VDD) 3.0V < VDD < 5.0V · Amplifier Supply Voltage 2.7V < VAMP < 8.5V LM4962 LM4962 Evaluation Board LM4962 LM4962 Evaluation Board Demo Board Schematic 20178811 AN-1441 AN-1441 FIGURE 1. Demo Board Schematic © 2006 National Semiconductor Corporation AN201788 AN201788 www.national.com AN-1441 AN-1441 TABLE 1. Demo Board Connections Designator Label J1 IN A Function Single Ended Audio Input Signal A (LM4962 LM4962) J2 OUTA J3 SD Boost Boost Converter Shutdown J3 open = Shutdown J3 shorted = Active J4 SD AmpB Amplifier B Shutdown (LM4951 LM4951) J4 open = Shutdown J4 shorted = Active J5 SD AmpA Amplifier A Shutdown (LM4962 LM4962) J5 open = Shutdown J5 shorted = Active J6 IN B J7 OUTB J8 GND VDD J9 J10 BTL Audio Output Signal A (LM4962 LM4962) Single Ended Audio Input Signal B (LM4951 LM4951) BTL Audio Output Signal B (LM4951 LM4951) Power Supply Connection Stereo/Mono select J9 Shorted = Stereo J9 Open = Mono Flagout Flagout pin to monitor Over Voltage or Over Current conditions quired for stability (see Figure 1). Adding this capacitor puts a zero in the loop response of the converter. The recommended frequency for the zero's 3dB point should be approximately 60kHz. C3 can be calculated using the formula: Start-Up Sequence For the LM4962 LM4962 correct start-up sequencing is important for optimal device performance. Using the correct start up sequence will improve click/pop performance as well as avoid transients that could reduce battery life. For ringer/ loudspeaker mode, the supply voltage should be applied first and both the boost and the amplifier should be in shutdown (J3 & J5 open). Then the boost converter can be activated (J3 shorted) followed by the amplifier (J5 shorted). If the boost converter shutdown is toggled while the amplifier is active an audible pop will be heard. C3 = 1 / (2 x R2 x fz) PCB Layout Guidelines High frequency boost converters require very careful layout of components in order to get stable operation and low noise. All components must be as close as possible to the LM4962 LM4962 device. It is recommended that a 4-layer PCB be used so that internal ground planes are available. See Figures 611 for demo board reference schematic and layout. Some additional guidelines to be observed: 1. Keep the path between L1, D2, and C2 extremely short. Parasitic trace inductance in series with D2 and C2 will increase noise and ringing. Setting the Output Voltage (V1) of Boost Converter The output voltage is set using the external resistors R2 and R5 (see Figure 1). A value of approximately 25k is recommended for R2 to establish the open loop gain of the boost converter. The output voltage of the boost converter can be calculated using the equation: V1 = VFB [1 + (R2 / R5)] 2. If internal ground planes are available (recommended) use vias to connect directly to ground at the GND (SW) and GND pins of U1, as well as the negative sides of capacitors Cs1 and C2. 3. To ensure correct operation of this device, it is essential that the GND (SW) pin (A3), GND pin (D1), and the negative side of Cs2 be connected to the same GND plane. Cs2 should be placed as close as possible to these two GND planes. Feed-Forward Compensation For Boost Converter Although the LM4962 LM4962's internal Boost converter is internally compensated, an external feed-forward capacitor, Cf, is re- www.national.com 2 This section provides practical guidelines for PCB layouts. Designers should note that these are only "rule-of-thumb" recommendations and the actual results will depend heavily on the final layout. AVOIDING TYPICAL DESIGN / LAYOUT PROBLEMS Avoid ground loops or running digital and analog traces parallel to each other (side-by-side) on the same PCB layer. When traces must cross over each other do it at 90 degrees. Running digital and analog traces at 90 degrees to each other from the top to the bottom side as much as possible will minimize capacitive noise coupling and crosstalk. POWER AND GROUND CIRCUITS For multi-layer boards, it is important to isolate the switching power and ground trace paths from the amplifier power and ground trace paths. Star trace routing techniques (bringing individual traces back to a central point rather than daisy chaining traces together in a serial manner) can have a major impact on low level signal performance. Star trace LM4962 LM4962 EVALUATION BOARD BILL OF MATERIALS Item Description Package U1 Ceramic Speaker Driver Value Notes TLA2011A TLA2011A U2 Audio Power Amplifier TLA09ZZA TLA09ZZA Cf1, Cf3 Ceramic Capacitor 1210 82pF, 50V 50V C3 Ceramic Capacitor 1210 100pF, 50V 50V CinA, CinB Ceramic Capacitor 1210 0.39µF, 50V C2, Cs1, Cs2, Cs3 Ceramic Capacitor 1210 4.7µF, 16V Css Ceramic Capacitor 1210 10nF, 16V Cb1, Cb2 Tantalum Capacitor 1210 1µF, 16V D2 Schottky Diode SOD-123 20V, 0.5A On Semi MBR0520 MBR0520 L1 Inductor 4.3mm X 4.8mm X 3.5mm 10µH, 1.04A Sumida CR43100 R3 Resistor 0603 1.6k 1/10W 1/10W, 5% low ESR, ESR < 50 R2 Resistor 0603 25k 1/10W 1/10W, 5% Rpu, Rpu2, Rpu3, Rchg1, Rchg2, Resistor 0603 1k 1/10W 1/10W, 5% Rpu4 Resistor 0603 100k 1/10W 1/10W, 5% RinA, RinB, Rf2 Resistor 0603 20k 1/10W 1/10W, 5% Rf1, Rf3 Resistor 0603 200k 1/10W 1/10W, 5% Rchg1, Rchg2 Resistor 0603 1k 1/10W 1/10W, 5% R4 Resistor 0603 4.9k 1/10W 1/10W, 5% R3 Resistor 0603 100m 1/10W 1/10W, 5% 3 www.national.com AN-1441 AN-1441 routing refers to using individual traces to feed power and ground to each circuit or even device. This technique will require a greater amount of design time but will not increase the final price of the board. General Layout Recommendations AN-1441 AN-1441 PCB Layout 20178806 FIGURE 2. Top Layer (Shown with Top Silkscreen visible) www.national.com 4 AN-1441 AN-1441 PCB Layout (Continued) 20178807 FIGURE 3. Mid Layer 1 (Shown with Top Silkscreen visible) 5 www.national.com AN-1441 AN-1441 PCB Layout (Continued) 20178808 FIGURE 4. Mid Layer 2 (Shown with Top Silkscreen visible) www.national.com 6 AN-1441 AN-1441 PCB Layout (Continued) 20178809 FIGURE 5. Bottom Layer (Shown with Top Silkscreen visible) 7 www.national.com AN-1441 AN-1441 PCB Layout (Continued) 20178810 FIGURE 6. Top Silkscreen www.national.com 8 AN-1441 AN-1441 Revision Table Rev Date Description 0.1 04/20/06 Initial release. 9 www.national.com LM4962 LM4962 Evaluation Board 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. For the most current product information visit us at www.national.com. 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 AND GENERAL COUNSEL 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. 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. BANNED SUBSTANCE COMPLIANCE National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2 CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2 CSP-9-111S2) and contain no ``Banned Substances'' as defined in CSP-9-111S2 CSP-9-111S2. AN-1441 AN-1441 Leadfree products are RoHS compliant. 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