System Board 6692

MAXREFDES1170: 24V/100mA, Iso-Buck DC-DC Converter Using the MAX17681A

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Input Type VIN (MIN)
Isolated/Non-Isolated Topology
DC 17 36 0.1 Single 25.2 2.4 Isolated Synchronouse 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 over-current protection. The MAX17681/MAX17681A is available in a compact 10-pin (3mm × 2mm) TDFN package. Simulation models are available.

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

This reference design is derived from the MAX17681AEVKITF. The three main differences between MAXREFDES1170 and the MAX17681AEVKITF are as follows:

  • The board size of the MAXREFDES1170 is 20mm × 40mm, which is approximately one-quarter the size of the MAXREFDES17681AEVKITF.
  • The pin distances of the MAXREFDES1170 are consistent with Distributed-power Open Standards Alliance (DOSA) open standards for DC/DC brick power supplies.
  • The reference design has two transformer options, one is from Wurth and the other is from the transformer vendor HanRun.

With the above three features, customers can reduce the whole solution size and cost. Customers can also mount this reference design on system boards.

MAXREFDES1170 Hardware Enlarge+

This board is not available for purchase.

Designed, Built, Tested

This reference design describes the hardware shown in Figure 1. 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.

Design Resources


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