LT1425 Isolated Flyback Switching Regulator UFEATURESDESCRIPTION ■ No Transformer “Third Winding” or Optoisolator The LT®1425 is a monolithic high power switching regu- Required lator specifically designed for the isolated flyback topol- ■ ± 5% Accurate Output Voltage Without User Trims ogy. No “third winding” or optoisolator is required; the (See Circuit Below) integrated circuit senses the isolated output voltage ■ Resistor Programmable Output Voltage directly from the primary side flyback waveform. A high ■ Regulation Maintained Well Into Discontinuous current, high efficiency switch is included on the die along Mode (Light Load) with all oscillator, control and protection circuitry. ■ Optional Load Compensation The LT1425 operates with input supply voltages from 3V ■ Operating Frequency: 285kHz to 20V and draws only 7mA quiescent current. It can ■ Easily Synchronized to External Clock deliver output power up to 6W with no external power ■ Available in 16-Pin Narrow SO Package devices. By utilizing current mode switching techniques, it U provides excellent AC and DC line regulation. APPLICATIONS The LT1425 has a number of features not found on other ■ Isolated Flyback Switching Regulators switching regulator ICs. Its unique control circuitry can ■ Ethernet Isolated 5V to – 9V Converters maintain regulation well into discontinuous mode in most ■ Medical Instruments applications. Optional load compensation circuitry allows ■ Isolated Telecom Supplies for improved load regulation. An externally activated shut- down mode reduces total supply current to 15µA for , LTC and LT are registered trademarks of Linear Technology Corporation. standby operation. UTYPICAL APPLICATION5V to Isolated – 9VOUTLoad Regulation 500V ISOLATION BARRIER 9.5 5V 9.4 T1* V – + C1 9.3 C2 ISOLATED D1 100µF 12 47µF 9.2 1N5819 + –9V ± 5% AT 10V 16V 20mA TO 200mA VIN 11 • • 9.1 VSW R1 9.0 22.6k F LT1425 1% 8.9 *DALE LPE 4841-330MB 15 3 SHDN RFB 8.8 6 R2 OUTPUT VOLTAGE (V) SYNC 3.01k 8.7 4 5 1% V R C REF 8.6 C3 14 R 1000pF OCOMP 8.5 13 R R3 0 50 100 150 200 CCOMP C4 15k OUTPUT CURRENT (mA) SGND PGND 0.1µF 7 10 1425 TA02 1425 TA01 1
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