MAXREFDES1281: 26V 400mA Iso-Buck DC DC Converter Using the MAX17682


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Reference Guide


The MAXREFDES1281 is an iso-buck converter which delivers up to 400mA at 26V VOUT, from 18V to 36V VIN. It is designed for industrial equipment that needs an isolated voltage from the above input supply voltage range. The MAXREFDES1281 illustrates techniques using the iso-buck converter to generate an isolated output. This document explains how the MAX17682 iso-buck converter can be used to generate 26V from 18V to 36V input voltage.

The MAX17682 is a high-voltage, high-efficiency, iso-buck DC-DC converter designed to provide isolated power up to 10W. The device operates over a wide 4.5V to 42V input voltage range and uses primary-side feedback to regulate the output voltage. It delivers primary peak current up to 3.7A and regulates primary output voltage to within ±1.2% over -40°C to +125°C.

The device features peak-current-mode control with pulse-width modulation (PWM) scheme. The low-resistance, on-chip MOSFETs ensure high efficiency at full load and simplify the layout.

A programmable soft-start feature allows users to reduce input inrush current. The device also incorporates an output enable/undervoltage lockout pin (EN/UVLO) that allows the user to turn on the part at the desired inputvoltage level. An open-drain RESETB pin provides a delayed power-good signal to the system upon achieving successful regulation of the primary output voltage.

The device operates over the -40°C to +125°C industrial temperature range and is available in a compact 20-pin (4mm x 4mm) TQFN package. Simulation models are available.


  • Eliminates External Components, Reduces Total Cost
    • Synchronous Primary Operation for High Efficiency and Reduced Cost
    • All-Ceramic Capacitors, Ultra-Compact Layout
  • Reduces Number of DC-DC Regulators to Stock
    • Wide 4.5V to 42V Input Voltage Range
    • 0.9V to 92% VIN Primary Output Voltage
    • Delivers Up to 3.7A Peak Current
    • 100kHz to 500kHz Adjustable Frequency with External Synchronization

  • Reduces Power Dissipation
    • Peak Efficiency > 90%
    • Shutdown Current = 2.8μA (typ)



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PCB Layout


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Test Results


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Maxim Devices (1)

Part Number Name Product Family Order Design kits and evaluation modules
MAX17682 4.5V to 42V Input, Ultra-Small, High-Efficiency, Iso-Buck DC-DC Converter Isolated Power Buy Now

Maxim Devices (1)

Part Number Product Family
Isolated Power
4.5V to 42V Input, Ultra-Small, High-Efficiency, Iso-Buck DC-DC Converter

Design Files (6)

Title Type Size Date
MAXREFDES1281 Assembly Bottom PDF 541KB 2021-11-21
MAXREFDES1281 Assembly Top PDF 586KB 2021-11-21
MAXREFDES1281 BOM CSV 3KB 2021-11-21
MAXREFDES1281 PCB PDF 987KB 2021-11-21
MAXREFDES1281 Schematic PDF 16KB 2021-11-21
MAXREFDES1281 Test Result PDF 213KB 2021-11-21
Date Type

MAXREFDES1281 Assembly Bottom

(PDF, 541KB)


MAXREFDES1281 Assembly Top

(PDF, 586KB)



(CSV, 3KB)



(PDF, 987KB)


MAXREFDES1281 Schematic

(PDF, 16KB)


MAXREFDES1281 Test Result

(PDF, 213KB)

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