MAXREFDES1012: 10.6W, no optocoupler, flyback DC-DC converter

The MAX17690 is a peak-current-mode, fixed-switching-frequency controller specifically designed for use in isolated flyback structures operating in discontinuous conduction mode (DCM). The device directly senses the isolated output voltage of the primary flyback waveform during the primary switch turn-off period, eliminating the need for an auxiliary winding or optocoupler to regulate the output voltage.  

The MAX17690 operates over a wide power supply range of 4.5V to 60V. Switching frequency is programmable from 50kHz to 250kHz. The MAX17690 provides input overvoltage protection through the OVI pin. The MAX17690's internal LDO output is 7V, making it ideal for switching standard MOSFETs used in logic-level and flyback converters. Sourcing/sinking 2A/4A, the MAX17690 is ideal for driving low RDS(on) power MOSFETs with fast gate transition times. The MAX17690 provides an adjustable soft-start feature to limit inrush current during startup.  

The MAX17690 provides temperature compensation to compensate for the output diode forward voltage drop. The MAX17690 features reliable hiccup and thermal protection, is available in a space-saving 16-pin 3mm x 3mm TQFN package, and operates over the -40°C to 125°C temperature range. 

Key Features

• No optocoupler or third winding required
• 2A/4A maximum source/sink gate drive current
• Programmable switching frequency from 50kHz to 250kHz
• Enter EN/UVLO function
• Input overvoltage protection
• Programmable soft start
• Hiccup Mode Short Circuit Protection
• Thermal shutdown protection
• -40℃ to +125℃ operating temperature range
• Space-saving, 3mm x 3mm, 16-pin TQFN package

This circuit board is not for sale.

Demonstrates an optocouplerless, flyback DC-DC converter using the MAX17690 for a 5.3V DC output application. Power supplies up to 2A @ 5.3V.

Design, build and test

This document introduces the hardware shown in Figure 1 and provides detailed, systematic technical guidance for designing an isolated, optocouplerless, flyback DC-DC converter using Maxim's MAX17690 controller. The power supply has been built and tested.

Design Resources