The MAX17690 is a peak current mode, fixed-frequency switching controller specifically designed for the isolated flyback topology operating in Discontinuous Conduction Mode (DCM). The device senses the isolated output voltage directly from the primary-side flyback waveform during the off-time of the primary switch. No auxiliary winding or optocoupler is required for output voltage regulation.

The MAX17690 is designed to operate over a wide supply range from 4.5V to 60V. The switching frequency is programmable from 50kHz to 250kHz. The MAX17690 provides an input overvoltage protection through the OVI pin. The 7V internal LDO output of the MAX17690 makes it suitable for switching both logic-level and standard MOSFETs used in flyback converters. With 2A/4A source/ sink currents, the MAX17690 is ideal for driving low R_DS(ON) power MOSFETs with fast gate transition times. The MAX17690 provides an adjustable soft-start feature to limit the inrush current during startup.

The MAX17690 provides temperature compensation for the output diode forward-voltage drop. The MAX17690 has robust hiccup-protection and thermal protection schemes, and is available in a space-saving 3mm x 3mm 16-pin TQFN package with a temperature range from -40°C to +125°C.

Key Features

• No Optocoupler or Third Winding Required
• 2A/4A Peak Source/Sink Gate Drive Currents
• 50kHz to 250kHz Programmable Switching Frequency
• Input EN/UVLO Feature
• Input Overvoltage Protection
• Programmable Soft-Start
• Hiccup-Mode Short-Circuit Protection
• Thermal Shutdown Protection
• -40°C to +125°C Operating Temperature Range
• Space-Saving, 3mm x 3mm, 16-Pin TQFN Package

This board is not available for purchase.

A no-opto flyback DC-DC converter using the MAX17690 is demonstrated for a 54V DC output application. The power supply delivers up to 1.1A at 54V.

Designed, Built, Tested

This document describes the hardware shown in Figure 1. It provides a detailed systematic technical guide to designing a no-opto flyback using Maxim’s MAX17690 current-mode controller. The power supply has been built and tested, details of which follow later in this document.

Design Resources