Features

• Drives External Power MOSFET
• Supply Voltage Range: 4.5V to 20V
• Flyback Voltage Limited Only by External Components
• Senses Output Voltage Directly from Primary Side Winding—No Optoisolator Required
• Moderate Accuracy Regulation Without User Trims
• Regulation Maintained Well into Discontinuous Mode
• Switching Frequency from 50kHz to 250kHz with External Capacitor
• Available in 16-Pin GN and SO Packages
• Optional Load Compensation
• Optional Undervoltage Lockout
• External I_SENSE Resistor
• Shutdown Feature Reduces I_Q to 50µA Typ

Typical Application

Description

The LT1737 is a monolithic switching regulator controller specifically designed for the isolated flyback topology. It drives the gate of an external MOSFET and is generally powered from a DC supply voltage. Output voltage feedback information may be supplied by a variety of methods including a third transformer winding, the primary winding or even direct DC feedback (see Applications Information). Its gate drive capability coupled with a suitable external MOSFET and other power path components can deliver load power up to tens of Watts.

The LT1737 has a number of features not found on other isolated flyback controller ICs presently available. By utilizing current mode switching techniques, it provides excellent AC and DC line regulation. Its unique control circuitry can maintain regulation well into discontinuous mode in most applications. Optional load compensation circuitry allows for improved load regulation. An optional undervoltage lockout pin halts operation when the application input voltage is too low. An optional external capacitor implements a soft-start function.