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LINEAR Design Note 501 Manual

1. DESIGN NOTES 60V Buck Boost Controller Drives High Power LEDs Charges Batteries and Regulates Voltage with Up to 98 5 Efficiency at 100W and Higher Design Note 501 Keith Szolusha Introduction The LT 3791 is a 4 switch synchronous buck boost DC DC converter that regulates both constant current and constant voltage at up to 98 5 efficiency with a single inductor It can deliver hundreds of watts and features a 60V input and output rating making it ideal for driving high power LED strings and charging high voltage batteries when both step up and step down conversion is needed It can also be used as a constant voltage buck boost regulator with current limiting and monitoring for both input and output Buck Boost Controller Drives 100W LED String for Airplane and Truck Lights Airplanes and big trucks with 24V batteries need pow erful efficient and robust headlights and spotlights Figure 1 shows a 33 3V 3A nine Luminus SSR 90 LEDs Vin 15V TO 58V LT3791 SHORTLED OPENLED PWM DIM 86 6k 300kHz 10nF D1 BAT46WJ L1 COOPER HC9 100 R M1 M2 RENESAS RJK0651DPB M3 M5 RENESAS RJK0451DPB buck boost LED driver that runs from 15V to 58V input with up to 98 5 efficiency The 4 switch synchronous topology drives high power LEDs with minimal switch power loss and minimal temperature rise Unlike other topologies the LT3791 buck boost can be shorted
2. from LED to both LED and GND and as a feature can be programmed to latch off or keep trying to turn back on if the short is removed Diagnostic output flags report both short circuit and open LED conditions The solution in Figure 1 features up to 100 1 PWM dim ming at 100Hz for accurate brightness adjustment with out color shift and analog LED dimming when a PWM oscillator is not present 4J LI LTC LTM Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation All other trademarks are the property of their respective owners 98 BOOST BUCK Ac BUCK BOOST EFFICIENCY amp 33 3V 3A LEDs oy 1 ar 15 20 25 30 35 40 45 50 55 60 sy NPUT VOLTAGE V SM ssr90 Figure 2 Efficiency of oy 2 Figure 1 4 g Figure 1 15 58Vjy to 33 3V 3A LED Driver with Up to 98 5 Efficiency 04 12 501 36V 2 5ASLA Battery Charger The buck boost converter shown in Figure 3 charges a 36V 12Ah SLA battery at 44V with 2 5A DC froma 9V to 58V input Specially integrated C 10 current sensing and battery voltage detection drops the battery voltage from its charging voltage 44V to its float voltage 41V when the battery is near full charge The OPENLED flag is used to change the state of the charger from charge to float When the battery voltage drops far enough voltage feed back returns the charger to its char
3. ge state The LT3791 can be tailored to charge a range of bat tery chemistries and capacities from a variety of input sources regardless of the voltage relationship between them An external microcontroller can be programmed and used to create a maximum power point tracking de vice to charge the battery from a solar panel The output diagnostics and dimming input pins make this a simple interface for high power solar panel applications design 120W 6V to 55V Voltage Regulator The LT3791 can also be used in high power constant voltage buck boost applications The FB pin doubles as both the main voltage feedback for the buck boost and the overvoltage protection detection and regulation when used as an LED driver PVin 9V TO 58V LT3791 SHORTLED PWMOUT CHARGE CURRENT CONTROL 86 6k D1 D2 BAT46WJ T L L1 W RTH 74435571100 10H 7 M1 M5 RENESAS RJKO651DPB Figure 1 can be easily turned into a 100W voltage regu lator with Voyy between 6V and 55V by placing a 100k resistor between the SSand Vper pins to defeat soft start reset during a fault The voltage regulator is short circuit proof The SHORTLED flag reports when there is a short circuit on the output The input current monitor can still be used in constant voltage regulation to protect any system that is input current limited RLgp sets the output current limit for short circuit but can be removed to provide a PGOOD flag using OPENLED by shorting ISP t
4. o ISN Conclusion The LT3791 synchronous buck boost controller deliv ers 100W and higher power at up to 98 5 efficiency to anumber of different loads The wide 4 7V to 60V input and OV to 60V output voltage range make it both power ful and versatile and its short circuit capability makes this a robust choice for many applications in potentially hazardous environments This seemingly limitless IC can be used in applications where atypical buck or boost converter cannot because of the crossover of input and output voltage ranges Rs1 2 5A 0 042 y CHARGE 36V SLA BATTERY AGM TYPE 4V FLOAT 44V CHARGE AT 25 C Z pso1 F03 Figure 3 36V 2 5A SLA Battery Charger with C 10 Charge Termination Data Sheet Download www linearcom Linear Technology Corporation 1630 McCarthy Blvd Milpitas CA 95035 7417 408 432 1900 FAX 408 434 0507 e www linear com For applications help call 408 432 1900 Ext 3801 dn501f LT AP 0412 196K PRINTED IN THE USA TECHNOLOGY LINEAR TECHNOLOGY CORPORATION 2012

LINEAR Design Note 501 Manual

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