LT1425 Isolated Flyback Switching Regulator FEATURES DESCRIPTION n No Transformer Third Winding or Optoisolator The LT 1425 is a monolithic high power switching regula- Required tor specifically designed for the isolated flyback topology. n 5% Accurate Output Voltage Without User Trims No third winding or optoisolator is required the inte- (See Circuit Below) grated circuit senses the isolated output voltage directly n Resistor Programmable Output Voltage from the primary side flyback waveform. A high current, n Regulation Maintained Well Into Discontinuous high efficiency switch is included on the die along with all Mode (Light Load) oscillator, control and protection circuitry. n Optional Load Compensation The LT1425 operates with input supply voltages from n Operating Frequency: 285kHz 3V to 20V and draws only 7mA quiescent current. It can n Easily Synchronized to External Clock deliver output power up to 6W with no external power n Available in 16-Pin Narrow SO Package devices. By utilizing current mode switching techniques, it provides excellent AC and DC line regulation. APPLICATIONS The LT1425 has a number of features not found on other n Isolated Flyback Switching Regulators switching regulator ICs. Its unique control circuitry can n Ethernet Isolated 5V to 9V Converters maintain regulation well into discontinuous mode in most n Medical Instruments applications. Optional load compensation circuitry allows n Isolated Telecom Supplies for improved load regulation. An externally activated shutdown mode reduces total supply current to 15A for standby operation. All registered trademarks and trademarks are the property of their respective owners. TYPICAL APPLICATION 5V to Isolated 9V Load Regulation OUT 9.5 500V 9.4 ISOLATION BARRIER 5V 9.3 T1* V 9.2 + C1 C2 ISOLATED D1 100F 12 47F 9V 5% AT 9.1 1N5819 10V 16V 20mA TO 200mA V IN 11 9.0 V SW R1 8.9 F 22.6k LT1425 1% 8.8 *DALE LPE 4841-330MB 3 15 SHDN R FB 8.7 R2 6 SYNC 3.01k 8.6 1% 4 5 R V REF C 8.5 C3 14 0 50 100 150 200 R OCOMP 1000pF 13 OUTPUT CURRENT (mA) R3 R CCOMP C4 15k 1425 TA02 SGND PGND 0.1F 7 10 1425 TA01 Rev. B 1 Document Feedback For more information www.analog.com OUTPUT VOLTAGE (V) +LT1425 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Supply Voltage ..........................................................20V GND 1 16 GND Switch Voltage ........................................................35V NC 2 15 SHDN SHDN, SYNC Pin Voltage ............................................7V R 3 14 R FB OCOMP R Pin Current .......................................................2mA FB V 4 13 R C CCOMP Operating Junction Temperature Range R 5 12 V REF IN LT1425C ............................................... 0C to 125C SYNC 6 11 V SW LT1425I ............................................ 40C to 125C SGND 7 10 PGND Storage Temperature Range .................. 65C to 150C GND 8 9 GND Lead Temperature (Soldering, 10 sec) ...................300C S PACKAGE 16-LEAD PLASTIC SO T = 145C, = 75C/W JMAX JA ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT1425CS PBF LT1425CS TRPBF 1425 16-Lead Plastic SOIC 0C to 125C LT1425IS PBF LT1425IS TRPBF 1425 16-Lead Plastic SOIC 40C to 125C Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with TRMPBF suffix. ELECTRICAL CHARACTERISTICSThe l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25C. V = 5V, T = 25C, V Open, V = 1.4V, unless otherwise specified. A IN J SW C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Feedback Amplifier I Reference Current Measured at R Pin with R = 3.000k 402 408 414 A REF FB REF l 396 420 A I R Pin Input Curren 500 nA IN REF l g Feedback Amplifier Transconductance = 10A (Note 2) 400 1000 1600 mho m IC l I , I Feedback Amplifier Source or Sink Current 30 50 80 A SOURCE SINK V Feedback Amplifier Clamp Voltage 1.9 V CL Reference Voltage/Current Line Regulation 5V V 18V l 0.01 0.04 %/V IN Voltage Gain (Note 3) 500 V/V V Sense Error l 10 25 mV IN Output Switch BV Output Switch Breakdown Voltage I = 5mA l 35 50 V C V(V ) Output Switch On-Voltage I = 1A l 0.55 0.85 V SW SW I Switch Current Limit Duty Cycle = 50%, 0C T 125C l 1.35 1.60 1.95 A LIM J Duty Cycle = 50%, 40C T 125C 1.2 1.60 1.95 A J Duty Cycle = 80% 1.30 A Current Amplifier Control Pin Threshold Duty Cycle = Minimum 0.95 1.2 1.3 V l 0.85 1.4 V Rev. B 2 For more information www.analog.com