System Board 6699

MAXREFDES1169: ±15V/75mA and ±7.5V/75mA, Iso-Buck DC-DC Converter Using the MAX17681A

 Download Reference Design Note

Input Type VIN (MIN)
Isolated/Non-Isolated Topology
DC 17 36 0.075 Multiple
-16.5 to 16.5 3.375 Isolated Iso-Buck

The MAX17681/MAX17681A is a high-voltage, high-efficiency, iso-buck DC-DC converter designed to provide isolated power up to 5W. The device operates over a wide 4.5V to 42V input and uses primary-side feedback to regulate the output voltage. The MAX17681/MAX17681A uses peak-current-mode control. Low-resistance, on-chip MOSFETs ensure high efficiency at full load while simplifying the PCB layout. The MAX17681/MAX17681A devices generate a well-regulated primary side voltage, which is then scaled by a suitable transformer turns ratio to derive isolated secondary output rails. While both the MAX17681 and MAX17681A support primary side overcurrent protection, the MAX17681A is an enhanced design that also supports robust secondary-side overcurrent protection. The MAX17681/MAX17681A is available in a compact 10-pin (3mm × 2mm) TDFN package. Simulation models are available.

MAXREFDES1169 Board Enlarge+

This board is not available for purchase.

Key Features

  • Reduces External Components and Total Cost
    • No Optocoupler
    • Synchronous Primary Operation
    • All-Ceramic Capacitors, Compact Layout
  • Reduces Number of DC-DC Regulators to Stock
    • Wide 4.5V to 42V Input
    • 0.9V to 0.96 x VIN Primary Output Voltage
    • Delivers Up to 5W Output Power
  • Reduces Power Dissipation
    • Peak Efficiency > 90%
    • 0.9μA (typ) Shutdown Current
  • Operates Reliably in Adverse Industrial Environments
    • Peak and Sink Current-Limit Protection
    • Robust Secondary-Side Output Overcurrent Protection (MAX17681A)
    • ±1.7% Feedback Accuracy
    • Programmable EN/UVLO Threshold
    • Adjustable Soft-Start
    • Overtemperature Protection
    • -40°C to +125°C Operation

Design Resources

Designed, Built, Tested

This reference design describes the hardware shown. It provides a detailed systematic technical guide to design an iso-buck converter using Maxim’s MAX17681A current mode controller. The power supply has been built and tested, details of which follow later in this document.


4V to 60V, 100mA, Ultra-Low Quiescent Current, Linear Regulator

  • Extremely Easy to Use
  • Reduces Number of Linear Regulators to Stock
  • Operates Reliably in Adverse Industrial Environments

4.5V to 42V Input, High-Efficiency, Iso-Buck DC-DC Converter

  • Reduces External Components and Total Cost
  • Reduces Number of DC-DC Regulators to Stock
  • Reduces Power Dissipation