LT1737 High Power Isolated Flyback Controller FEATURES DESCRIPTIO Drives External Power MOSFET The LT 1737 is a monolithic switching regulator control- Supply Voltage Range: 4.5V to 20V ler specifically designed for the isolated flyback topology. Flyback Voltage Limited Only by It drives the gate of an external MOSFET and is generally External Components powered from a DC supply voltage. Output voltage feed- Senses Output Voltage Directly from Primary Side back information may be supplied by a variety of methods WindingNo Optoisolator Required including a third transformer winding, the primary wind- Switching Frequency from 50kHz to 250kHz ing or even direct DC feedback (see Applications Informa- with External Capacitor tion). Its gate drive capability, coupled with a suitable Moderate Accuracy Regulation Without User Trims external MOSFET and other power path components, can Regulation Maintained Well into Discontinuous Mode deliver load power up to tens of Watts. External I Resistor SENSE The LT1737 has a number of features not found on other Optional Load Compensation isolated flyback controller ICs. By utilizing current mode Optional Undervoltage Lockout switching techniques, it provides excellent AC and DC line Shutdown Feature Reduces I to 50A Typ Q regulation. Its unique control circuitry can maintain regu- Available in 16-Pin GN and SO Packages lation well into discontinuous mode in most applications. Optional load compensation circuitry allows for improved U load regulation. An optional undervoltage lockout pin APPLICATIO S halts operation when the application input voltage is too Isolated Flyback Switching Regulators low. An optional external capacitor implements a soft- Medical Instruments start function. Instrumentation Power Supplies , LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATIO 12V-18V to Isolated 15V Converter R2 V IN 35.7k 1% + C1 T1 D1 22F COILTRONICS D2 MBRS1100 CTX150-4 BAS16 Q1 V = 15V OUT 2N3906 I = 300mA OUT + 240k C2 R4 150H 150H 33F 7.5k C3 33k 0.1F UVLO V CC M1 FB GATE IRFL014 LT1737 V I C SENSE R3 OSCAP t ENDLY MINENAB R R SGND PGND R1 ON OCMP CMPC 3.01k 0.27 1% NOTE: SEE APPLICATIONS 1nF 47pF 75k 150k 100k 4.7k 0.1F INFORMATION FOR ADDITIONAL COMPONENT SPECIFICATIONS 1737 TA01 1737fa 1 U ULT1737 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) V Supply Voltage................................................. 22V TOP VIEW ORDER PART CC UVLO Pin Voltage .................................................... V NUMBER CC PGND 1 16 GATE I Pin Voltage .................................................... 2V SENSE I 2 15 V SENSE CC LT1737CGN FB Pin Current ..................................................... 2mA SFST 3 14 t ON LT1737CS Operating Junction R 4 13 ENDLY OCMP LT1737IGN R 5 12 MINENAB Temperature Range CMPC LT1737IS OSCAP 6 11 SGND LT1737C ............................................... 0C to 100C V 7 10 UVLO C GN PART MARKING LT1737I ............................................ 40C to 125C FB 8 9 3V OUT Storage Temperature Range ................ 65C to 150C 1737 Lead Temperature (Soldering, 10 sec)................ 300C GN PACKAGE S PACKAGE 1737I 16-LEAD PLASTIC SSOP 16-LEAD PLASTIC SO T = 125C, = 110C/W (GN) JMAX JA T = 125C, = 110C/W (SO) JMAX JA Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are at T = 25C. V = 14V, GATE open, V = 1.4V unless otherwise noted. A CC C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Power Supply V Minimum Input Voltage 4.1 4.5 V CC(MIN) I Supply Current V = Open 10 15 mA CC C Shutdown Current V = 0V, V = Open 50 150 A UVLO C Feedback Amplifier V Feedback Voltage 1.230 1.245 1.260 V FB 1.220 1.270 V I Feedback Pin Input Current 500 nA FB g Feedback Amplifier Transconductance l = 10A 400 1000 1800 mho m C I , I Feedback Amplifier Source or Sink Current 30 50 80 A SRC SNK V Feedback Amplifier Clamp Voltage 2.5 V CL Reference Voltage/Current Line Regulation 4.75V V 18V 0.01 0.05 %/V IN Voltage Gain V = 1V to 2V 2000 V/V C Soft-Start Charging Current V = 0V 25 40 50 A SFST Soft-Start Discharge Current V = 1.5V, V = 0V 0.8 1.5 mA SFST UVLO Gate Output V Output High Level I = 100mA 11.5 12.1 V GATE GATE = 500mA 11.0 11.8 V I GATE Output Low Level I = 100mA 0.3 0.45 V GATE I = 500mA 0.6 1.0 V GATE I Output Sink Current in Shutdown, V = 0V V = 2V 1.2 2.5 mA GATE UVLO GATE t Rise Time C = 1000pF 30 ns r L t Fall Time C = 1000pF 30 ns f L 1737fa 2 U WWW