LM2622 600kHz/1.3MHz Step-up DC/DC Converter LM2622 step-up DC/DC

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LM2622 600kHz/1.3MHz Step-up DC/DC Converter LM2622 step-up DC/DC

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LM2622 600kHz/1.3MHz Step-up DC/DC Converter
LM2622 600kHz/1.3MHz Step-up DC/DC Converter
LM2622 step-up DC/DC converter with 1.6A, internal switch selectable operating frequency. With ability convert 3.3V multiple outputs -8V, 23V, LM2622 ideal part biasing displays. LM2622 operated switching frequencies 600kHz 1.3MHz allowing easy filtering noise. external compensation gives user flexibility setting frequency compensation, which makes possible small, ceramic capacitors output. LM2622 available profile 8-lead MSOP package.
Features
1.6A, 0.2, internal switch Operating voltage 2.0V 600kHz/1.3MHz selectable frequency operation Over temperature protection 8-Lead MSOP package
Applications
Bias Supplies Handheld Devices Portable Applications GSM/CDMA Phones Digital Cameras
Typical Application Circuit
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Operation
2004 National Semiconductor Corporation
DS101273
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LM2622
Connection Diagram
View
10127304
8-Lead Plastic MSOP Package Number MUA08A
Ordering Information
Order Number LM2622MM-ADJ LM2622MMX-ADJ Package Type MSOP-8 MSOP-8 Package Drawing MUA08A MUA08A Supplied 1000 Units, Tape Reel 3500 Units, Tape Reel S18B S18B Package
Description
Name SHDN FSLCT Output voltage feedback input. Shutdown control input, active low. Analog power ground. Power switch input. Switch connected between pin. Analog power input. Switching frequency select input. 1.3MHz. Ground 600kHz. Connect ground leave open. Connect directly beneath device possible. other traces otherwise possible directly connect leave this open shield from sources EMI. Function Compensation network connection. Connected output voltage error amplifier.
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LM2622
Block Diagram
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LM2622
Absolute Maximum Ratings (Note
Military/Aerospace specified devices required, please contact National Semiconductor Sales Office/ Distributors availability specifications. Voltage Voltage Voltage SHDN Voltage FSLCT Maximum Junction Temperature Power Dissipation(Note Lead Temperature 150°C Internally Limited 300°C
Vapor Phase sec.) Infrared sec.) Susceptibility (Note Human Body Model Machine Model
215°C 220°C
200V
Operating Conditions
Operating Junction Temperature Range (Note Storage Temperature Supply Voltage -40°C +125°C -65°C +150°C
Electrical Characteristics
Specifications standard type face 25°C those with boldface type apply over full Operating Temperature Range -40°C +125°C)Unless otherwise specified. =2.0V unless otherwise specified. Symbol ICL(Note VO/ILOAD %VFB/VIN DMAX ISHDN RDSON ThSHDN Parameter Quiescent Current Feedback Voltage Switch Current Limit Load Regulation Feedback Voltage Line Regulation Bias Current (Note Input Voltage Range Error Transconductance Error Voltage Gain Maximum Duty Cycle Switching Frequency Shutdown Current Switch Leakage Current Switch RDSON SHDN Threshold Threshold Threshold Thermal Resistance Junction Ambient(Note Junction Ambient(Note Junction Ambient(Note Junction Ambient(Note Junction Ambient(Note FSLCT Ground FSLCT VSHDN VSHDN 2.7V, Output High Output 1.25 0.01 -0.5 0.01 1.92 1.82 °C/W 2.7V (Note 3.3V 2.0V 12.0V Conditions (Not Switching) VSHDN 1.2285 (Note (Note 1.26 1.65 0.013 (Note 1.2915 Units mV/A µmho
Note Absolute maximum ratings limits beyond which damage device occur. Operating Ratings conditions which device intended functional, device parameter specifications guaranteed. guaranteed specifications test conditions, Electrical Characteristics. Note maximum allowable power dissipation function maximum junction temperature, TJ(MAX), junction-to-ambient thermal resistance, ambient temperature, Electrical Characteristics table thermal resistance various layouts. maximum allowable power dissipation ambient temperature calculated using: (MAX) (TJ(MAX) TA)/JA. Exceeding maximum allowable power dissipation will cause excessive temperature, regulator will into thermal shutdown. Note human body model capacitor discharged through 1.5k resistor into each pin. machine model 200pF capacitor discharged directly into each pin.
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LM2622
Electrical Characteristics
(Continued)
Note limits guaranteed room temperature (standard typeface) temperature extremes (bold typeface). room temperature limits 100% production tested. limits temperature extremes guaranteed correlation using standard Statistical Quality Control (SQC) methods. limits used calculate Average Outgoing Quality Level (AOQL). Note Typical numbers 25°C represent most likely norm. Note Duty cycle affects current limit ramp generator. Note Current limit duty cycle. TYPICAL PERFORMANCE section Switch Current Limit Note Bias current flows into pin. Note Junction ambient thermal resistance external heat sink) MSO8 package with minimal trace widths (0.010 inches) from pins circuit. "Scenario 'A'" Power Dissipation section. Note Junction ambient thermal resistance MSO8 package with minimal trace widths (0.010 inches) from pins circuit approximately 0.0191 copper heat sinking. "Scenario 'B'" Power Dissipation section. Note Junction ambient thermal resistance MSO8 package with minimal trace widths (0.010 inches) from pins circuit approximately 0.0465 copper heat sinking. "Scenario 'C'" Power Dissipation section. Note Junction ambient thermal resistance MSO8 package with minimal trace widths (0.010 inches) from pins circuit approximately 0.2523 copper heat sinking. "Scenario 'D'" Power Dissipation section. Note Junction ambient thermal resistance MSO8 package with minimal trace widths (0.010 inches) from pins circuit approximately 0.0098 copper heat sinking layer 0.0760 copper heat sinking bottom layer, with three 0.020 vias connecting planes. "Scenario 'E'" Power Dissipation section.
Typical Performance Characteristics
Efficiency Load Current (VOUT kHz) Efficiency Load Current (VOUT MHz)
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Switch Current Limit Temperature (VIN 3.3V, VOUT
Switch Current Limit
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LM2622
Typical Performance Characteristics
RDSON (ISW
(Continued) (600 kHz, switching)
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(600 kHz, switching)
(1.3 MHz, switching)
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(1.3 MHz, switching)
shutdown)
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LM2622
Typical Performance Characteristics
Frequency (600 kHz)
(Continued) Frequency (1.3 MHz)
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Load Transient Response (600 operation)
Load Transient Response (1.3 operation)
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Test circuit shown Figure
Test circuit shown Figure
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LM2622
Operation
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FIGURE Simplified Boost Converter Diagram First Cycle Operation Second Cycle Operation CONTINUOUS CONDUCTION MODE LM2622 current-mode, boost regulator. boost regulator steps input voltage higher output voltage. continuous conduction mode (when inductor current never reaches zero steady state), boost regulator operates cycles. first cycle operation, shown Figure (a), transistor closed diode reverse biased. Energy collected inductor load current supplied COUT. second cycle shown Figure (b). During this cycle, transistor open diode forward biased. energy stored inductor transferred load output capacitor. ratio these cycles determines output voltage. output voltage defined approximately
INTRODUCTION COMPENSATION
where duty cycle switch, will required design calculations. SETTING OUTPUT VOLTAGE output voltage using feedback resistor divider connected output shown typical operating circuit. feedback voltage 1.26V, ratio feedback resistors sets output voltage according following equation:
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FIGURE Inductor current. Diode current.
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LM2622
Operation
(Continued)
LM2622 current mode boost converter. signal flow this control scheme feedback loops, that senses switch current that senses output voltage. keep current programmed control converter stable above duty cycles 50%, inductor must meet certain criteria. inductor, along with input output voltage, will determine slope current through inductor (see Figure (a)). slope inductor current great, circuit will unstable above duty cycles 50%. 10µH inductor recommended most applications, while 4.7µH inductor used most 1.25 applications. duty cycle approaching maximum 85%, necessary increase inductance much Inductor Diode Selection more detailed inductor sizing. LM2622 provides compensation (VC) customize voltage loop feedback. recommended that series combination used compensation network, shown typical application circuit. given application, there exists unique combination that will optimize performance LM2622 circuit terms transient response. series combination introduces pole-zero pair according following equations:
where switching frequency, duty cycle, RDSON resistance internal switch taken from graph "RDSON VIN" Typical Performance Characteristics section. This equation only good duty cycles greater than 0.5), duty cycles less than recommended values used. corresponding inductor current ripple shown Figure given
where output impedance error amplifier, approximately 1Meg. most applications, performance optimized choosing values within range 200k used, High Output Capacitor Compensation) 680pF 4.7nF. Refer Applications Information section recommended values specific circuits conditions. Refer Compensation section other design requirement. COMPENSATION This section will present general design procedure help insure stable operational circuit. designs this datasheet optimized particular requirements. different conversions required, some components need changed ensure stability. Below general guidelines designing stable circuit continuous conduction operation (loads greater than approximately 75mA), most cases this will provide stability during discontinuous operation well. power components their effects will determined first, then compensation components will chosen produce stability. INDUCTOR DIODE SELECTION Although inductor sizes mentioned earlier fine most applications, more exact value calculated. ensure stability duty cycles above 50%, inductor must have some minimum value determined minimum input voltage maximum output voltage. This equation
inductor ripple current important reasons. reason because peak switch current will average inductor current (input current ILOAD/D') plus side note, discontinuous operation occurs when inductor current falls zero during switching cycle, greater than average inductor current. Therefore, continuous conduction mode occurs when less than average inductor current. Care must taken make sure that switch will reach current limit during normal operation. inductor must also sized accordingly. should have saturation current rating higher than peak inductor current expected. output voltage ripple also affected total ripple current. output diode boost regulator must chosen correctly depending output voltage output current. typical current waveform diode continuous conduction mode shown Figure (b). diode must rated reverse voltage equal greater than output voltage used. average current rating must greater than maximum load current expected, peak current rating must greater than peak inductor current. During short circuit testing, short circuit conditions possible application, diode current rating must exceed switch current limit. Using Schottky diodes with lower forward voltage drop will decrease power dissipation increase efficiency. GAIN OPEN-LOOP GAIN Since control stage converter forms complete feedback loop with power components, forms closedloop system that must stabilized avoid positive feedback instability. value open-loop gain will required, from which calculate, place, poles zeros determine crossover frequency phase margin. high phase margin (greater than 45°) desired best stability transient response. purpose stabilizing LM2622, choosing crossover point well below where right half plane zero located will ensure sufficient phase margin. discussion right half plane zero checking crossover using gain will follow. INPUT OUTPUT CAPACITOR SELECTION switching action boost regulator causes triangular voltage waveform input. capacitor required reduce input ripple noise proper operation regulator. size used dependant application board layout. regulator will loaded uniformly, with
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LM2622
Operation
(Continued)
very little load changes, lower current outputs, input capacitor size often reduced. size also reduced input regulator very close source output. size will generally need larger applications where regulator supplying nearly maximum rated output large load steps expected. minimum value 10µF should used less stressful condtions while 22µF 47µF capacitor required higher power dynamic loads. Larger values and/or lower needed application requires very ripple input source voltage. choice output capacitors also somewhat arbitrary depends design requirements output voltage ripple. recommended that (Equivalent Series Resistance, denoted RESR) capacitors used such ceramic, polymer electrolytic, tantalum. Higher capacitors used will require more compensation which will explained later section. also important because determines peak peak output voltage ripple according approximate equation: VOUT 2iLRESR Volts) minimum value 10µF recommended increased larger value. After choosing output capacitor determine pole-zero pair introduced into control loop following equations:
given Introduction Compensation section this pole area 10Hz 500Hz. frequency pole created determined equation:
where output impedance error amplifier, approximately 1Meg. Since generally much less than does have much effect above equation neglected until value chosen zero fZC. created cancel pole created output capacitor, fP1. output capacitor pole will shift with different load currents shown equation, setting zero exact. Determine range over expected loads then zero point approximately middle. frequency this zero determined
Where minimum load resistance corresponding maximum load current. zero created output capacitor generally very high frequency small. capacitors used neglected. higher capacitors used High Output Capacitor Compensation section. RIGHT HALF PLANE ZERO current mode control boost regulator inherent right half plane zero (RHP zero). This zero effect zero gain plot, causing imposed +20dB/decade rolloff, effect pole phase, subtracting another phase plot. This cause undesirable effects control loop influenced this zero. ensure zero does cause instability issues, control loop should designed have bandwidth less than frequency zero. This zero occurs frequency
chosen with selected value Check make sure that pole still 10Hz 500Hz range, change each value slightly needed ensure both component values recommended range. After checking design this section, these values changed little more optimize performance desired. This best done bench, checking load step response with different values until ringing overshoot output voltage edge load steps minimal. This should produce stable, high performance circuit. improved transient response, higher values should chosen. This will improve overall bandwidth which makes regulator respond more quickly transients. more detail required, most optimal performance desired, refer more depth discussion compensating current mode DC/DC switching regulators. HIGH OUTPUT CAPACITOR COMPENSATION When using output capacitor with high value, just improve overall phase margin control loop, another pole introduced cancel zero created ESR. This accomplished adding another capacitor, CC2, directly from compensation ground, parallel with series combination pole should placed same frequency fZ1, zero. equation this pole follows:
ensure this equation valid, that used without negatively impacting effects fPC2 must greater than 10fZC. CHECKING DESIGN final step check design. This ensure bandwidth less frequency zero. This done calculating open-loop gain, ADC. After this value known, calculate crossover visually placing -20dB/decade slope each pole, +20dB/ decade slope each zero. point which gain plot crosses unity gain, 0dB, crossover frequency. crossover frequency less than zero, phase margin should high enough stability. phase mar10
where ILOAD maximum load current. SELECTING COMPENSATION COMPONENTS first step selecting compensation components dominant frequency pole control loop. Simply choose values within ranges
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LM2622
Operation
(Continued)
also improved adding discussed earlier section. equation given below with additional equations required calculation:
where minimum load resistance, minimum input voltage, error amplifier transconductance found Electrical Characteristics table, RDSON value chosen from graph "RDSON Typical Performance Characteristics section. LAYOUT CONSIDERATIONS input bypass capacitor CIN, shown typical operating circuit, must placed close This will reduce copper trace resistance which effects input voltage ripple additional input voltage filtering, 100nF bypass capacitor placed parallel with CIN, close pin, shunt high frequency noise ground. output capacitor, COUT, should also placed close copper trace connections COUT capacitor increase series resistance, which directly effects output voltage ripple. feedback network, resistors RFB1 RFB2, should kept close pin, away from inductor, minimize copper trace connections that inject noise into system. Trace connections made inductor schottky diode should minimized reduce power dissipation increase overall efficiency. more detail switching power supply layout considerations Application Note AN-1149: Layout Guidelines Switching Power Supplies.
0.072fs V/s)
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LM2622
Application Information
10127308
FIGURE Triple Output Bias (600 operation) TRIPLE OUTPUT BIAS circuit Figure shows LM2622 configured provide outputs -8V, 23V, convenient biasing displays. output regulated, while outputs unregulated. output generated typical boost topology. basic operation boost converter described OPERATION section. output voltage with RFB1 RFB2 mended insure converter stable duty cycles greater than 50%. Refer COMPENSATION section more information. output derived from diode inverter. During second cycle, when transistor open, conducts charges minus diode drop ()0.4V using Schottky). When transistor opens first cycle, conducts C1's polarity reversed with respect output producing -8V. output realized with series capacitor charge pumps. consists four stages: first stage includes LM2622 switch; second stage uses third stage includes LM2622 switch; final stage first stage, charges when LM2622 switch closed, which causes conduct when switch open. second stage, voltage across when switch open. However, because referenced output, voltage when
placed across RFB1 pseudo soft-start. compensation network chosen optimally stabilize converter. inductor also affects stability. When operating kHz, 10uH inductor recom-
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LM2622
Application Information
(Continued)
Component RFB1 RFB2 OPERATION
0.1µF 40.2k 7.5k 5.1k MBRM140T3 BAT54S BAT54S BAT54S
0.1µF MBRM140T3 BAT54S BAT54S BAT54S
referenced ground. third stage, appears across when switch closed. When switch opens, referenced output minus diode drop, which raises voltage with respect ground about 24V. Hence, fourth stage, charged when switch open. From first stage last, there three diode drops that make output voltage closer 3xVDIODE (about 22.8V 0.4V forward drop assumed). TABLE Components Circuits Figure Component COUT1 COUT2 CFB1 CFB2 10µH 10µF 10µF 3.9nF 0.1µF USED 10µF 4.7µF 4.7µH 22µF USED 1.5nF 15nF 560pF 22µF 4.7µF
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FIGURE operation
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LM2622
Application Information
(Continued)
OPERATION
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FIGURE operation POWER DISSIPATION output power LM2622 limited maximum power dissipation. maximum power dissipation determined formula (Tjmax TA)/JA where Tjmax maximum specidfied junction temperature (125°C), ambient temperature, thermal resistance package. dependant layout board shown below.
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LM2622
Application Information
(Continued)
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LM2622 600kHz/1.3MHz Step-up DC/DC Converter
Physical Dimensions
inches (millimeters) unless otherwise noted
LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT GENERAL COUNSEL NATIONAL SEMICONDUCTOR CORPORATION. used herein: Life support devices systems devices systems which, intended surgical implant into body, support sustain life, whose failure perform when properly used accordance with instructions provided labeling, reasonably expected result significant injury user. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that products packing materials meet provisions Customer Products Stewardship Specification (CSP-9-111C2) Banned Substances Materials Interest Specification (CSP-9-111S2) contain ``Banned Substances'' defined CSP-9-111S2.
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National does assume responsibility circuitry described, circuit patent licenses implied National reserves right time without notice change said circuitry specifications.

LM2622 600kHz/1.3MHz Step-up DC/DC Converter LM2622 step-up DC/DC

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