LM2623 Cookbook National Semiconductor Application Note 1221 John

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LM2623 Cookbook National Semiconductor Application Note 1221 John

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LM2623 Cookbook
LM2623 Cookbook
National Semiconductor Application Note 1221 John Fairbanks July 2003
LM2623 General Purpose, Boost Converter Circuit
next page shows generic application circuit LM2623 boost converters. LM2623 boost converter circuits very conventional, except ratio adaptive circuitry that used change duty cycle. These components adjust duty cycle match input/output voltage ratio requirements. provides drive current oscillator (frequency increases with lower resistance values). provide duty cycle adjustment. default duty cycle when left about 17%. value generally determines total amount charge transfer resulting duty cycle adjustment. Smaller values require larger values (more charge transfer) achieve same duty cycle adjustment percentage. When more than necessary necessary adjust duty cycle dynamically input output voltage ratio changes), omitted. Adding allows duty cycle change input output voltage ratio changes battery discharging portable applications. applications where fresh fully charged battery voltage close output voltage cells generating 3.3V), optimum duty cycle changes dramatically
battery discharges. correct these situations will optimize duty cycle voltage ratio minimize ripple overshoot caused stored energy coil. table values below application circuit next page should produce good performance application requirements stated. Recommended inductor values based input voltage, load current operating frequency. works well most LM2623 cell applications. works well most LM2623 LiIon three cell applications. output voltage dividing output voltage comparison reference pin. couples ripple from output directly into comparator When regulation, this triggers regulation limit each switching cycle. Triggering this limit allows comparator make voltage comparison from same direction (above limit) each switching cycle. This minimizes hysteretic component ripple. larger output capacitor recommended minimize ripple resulting from overshoot stored energy coil. rectifier diode should selected function peak currents efficiency requirements.
LM2623 Boost Converter Circuit Typical Applications Digital Cameras
20039401
Cells Cells Cells
Load Type Analog/Digital Motor Drive Motor Drive
VOUT 3.6V
182k 300k 300k
150k
Tant Tant Tant
AN-1221
2003 National Semiconductor Corporation
AN200394
www.national.com
AN-1221
Dual Output Supply CCD/LCD from Cell Input
This supply begins with general purpose, boost converter circuit. Conventional, plus minus doubler circuits then added generate regulated tracking, negative supply (nominally -7.5V). Since -7.5V supply tracks regulated, large capacitor required keep voltage close regulated value. supply regulated, smaller capacitor value used. Dual SOT-23 diode packages recommended minimize component count doubler circuits. Losses primary stage reflected both
-7.5V outputs, schottky capacitor recommended here. supply output supplied externally from minimum source. circuit shown will about Conversion efficiency primary stage typically over nominal loads. Efficiency final output stages will nominal loads. typical applications, usually goes through satisfy very ripple requirements CCD. -7.5V supply also need followed linear regulator filter used CCDs.
LM2623 Dual Output Converter Circuit Typical Applications Digital Cameras CCD/LCD Supply
20039402
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AN-1221
Transformer Coupled, (SEPIC) Converter LI-ION Cell Input
Transformer coupled solutions commonly used cases where multiple output voltages required. application shown below uses single output winding obtain 3.3V. Because inherent stability on/off control system
LM2623, control portion circuit does need change when multiple output windings added. circuit shown generic example generating number outputs from single Lithium-Ion cell, long 3.3V output used regulation. Efficiencies obtained generation 3.3V with this circuit configuration.
LM2623 Sepic Circuit Typical Applications Digital Cameras
20039403
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AN-1221
White Driver Application Circuits
Optimal drive circuits LEDs require reasonable current regulation very high efficiency. Since human cannot detect small variations light intensity, particularly when adjacent LEDs driven with same current, tight regulation tolerances used processor voltage sources necessary. Most power supply 1.2V bandgap references these typically used sense current current source applications. application circuit shown next page uses about drop series with LEDs sense current. This reduces losses circuit about current will usually held within input voltage, temperature, voltage process variations combined. Typical regulation much closer than that. application circuit shown below balanced circuit that draws essentially constant power from battery. Constant power with constant voltage load results constant current drive. oscillator supplied current through shunts current away from oscillator through current sense resistor, circuit balanced when voltage across approximately .6V. balance such
that input voltage changes offset decreases oscillator time". This results constant power being drawn from battery. Small current fluctuations change voltage across increase decrease oscillator drive compensate. This maintains balance. IC's change frequency with temperature very well matched change voltage with temperature. This also helps maintain balance. output pulse switch voltage divided through triggers regulation limit each time switch swings positive. When coil discharges energy, output voltage reduces falls below regulation limit. This turns oscillator back again supply goes through another switching cycle. Discharging coil energy each cycle makes time vary proportion time. power drawn from battery then linear with increases decreases time (rather than varying time" squared). circuit needs balanced with nominal parts given application. Once balanced, should keep current constant within voltage, temperature part variations. Conversion efficiencies (neglecting sensing resistor drop) will approach 90%. Over input power actually converted into power driving LEDs most input voltage output loading conditions.
LM2623 White Driver Circuit
20039404
IOUT 17.5
Cell Cell Cells Cells
900k 1.2M 845k 1.38M
1.2M 845k 1.33M
348k 348k 348k 348k
Note: small changes IOUT, adjust accordingly.
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LM2623 Cookbook
Boost Converter Single Cell Systems
LM2623 guaranteed start-up voltage 1.1V 25°C. start-up voltage below open circuit cell potential NiCad NiMH over entire operating range 85°C). This allows used single cell boost converters rechargeable systems (NiCad NiMH). Both supply oscillator drive need
"boot-strapped" from output after supply starts insure proper operation. rectifier recommended minimize voltage drop from input output during start-up millivolts. addition drives oscillator from output voltage after supply started Using both necessary allow duty cycle vary input voltage varies. Efficiencies achievable conversion from single cell 3.3V with circuit shown.
LM2623 Cell Converter Circuit Typical Applications Pager Digital Cameras
20039405
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.
National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: 180-530 Email: europe.support@nsc.com Deutsch Tel: 9508 6208 English Tel: 2171 Tel: 8790
critical component component life support device system whose failure perform reasonably expected cause failure life support device system, affect safety effectiveness.
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National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: jpn.feedback@nsc.com Tel: 81-3-5639-7560
AN-1221
National does assume responsibility circuitry described, circuit patent licenses implied National reserves right time without notice change said circuitry specifications.

LM2623 Cookbook National Semiconductor Application Note 1221 John

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