Analog Devices Inc./Maxim Integrated MAXREFDES111B#

Overview

MAXREFDES111B# from Maxim Integrated is a fully assembled, tested, and certified isolated 24V-to-5V flyback reference design delivering 2W (400mA) output with ±5% regulation accuracy, 79% peak efficiency at 24V input, and galvanic isolation up to 1500VDC. It implements the MAX17498B peak-current-mode controller with internal n-channel MOSFET, fixed 500kHz switching frequency, and through-hole mounting for rapid prototyping in industrial power systems.

For engineers reviewing the MAXREFDES111B# datasheet, MAXREFDES111B# pinout, MAXREFDES111B# application, or MAXREFDES111B# equivalent, this reference board provides verified schematics, layout files, BOM, Gerber data, transformer qualification (Sumida 06343-T588), and lab-tested performance across line/load/thermal transients - supporting fast integration into PLCs, process controllers, and isolated sensor interfaces.

Technical Context

The MAXREFDES111B# is a complete, board-level implementation of an isolated flyback converter using primary-side regulation via optocoupler feedback (U2/U3), RCD snubber (R1/C3/D1), and MAX17498B current-mode control. Input voltage range is 18V–36V with programmable UVLO (18V start) and OVI (36V shutdown), soft-start time of 5ms, and hiccup-mode overcurrent protection.

It delivers regulated +5V at up to 400mA (with 20% overrange capability), features cycle-by-cycle primary-side current limiting set to 1.3A via R6, and achieves 50mV_P-P output ripple at full load. Transformer T1 provides reinforced insulation and meets 1500VDC isolation per IEC 60950-1.

Key Specifications

Availability

MAXREFDES111B# is available at Aetrix Electronics and suitable for industrial control and automation, programmable logic controllers (PLC), and isolated sensor interface designs requiring stable component supply, quick-turn evaluation, and production-ready reference hardware.

Supply support for MAXREFDES111B# includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) is a semiconductor company specializing in analog, mixed-signal, and power-management ICs for industrial, automotive, and communications applications.

The MAXREFDES reference design series targets rapid development of certified, isolated power supplies - enabling engineers to bypass transformer selection risk and accelerate validation of safety-critical 24V-to-5V conversion in harsh environments.

FAQ

What is the input voltage range supported by the MAXREFDES111B#?

The MAXREFDES111B# operates over an input voltage range of 18V to 36V DC. This accommodates nominal 24V industrial supplies while providing margin for brownout (UVLO set at 18V) and overvoltage (OVI set at 36V) conditions. The EN/UVLO and OVI pins are configured using resistor dividers R3/R4/R5 to ensure reliable startup and fault shutdown behavior across the specified range. MAXREFDES111B# maintains regulation and protection functionality throughout this window.

Which transformer is qualified for use with the MAXREFDES111B#?

The MAXREFDES111B# is qualified with the Sumida 06343-T588 surface-mount transformer. This transformer provides galvanic isolation up to 1500VDC and is specifically validated for use with the MAXREFDES111B#'s circuit topology, component values, and thermal profile. Unlike MAXREFDES111A# (Wurth 750315847) or MAXREFDES111C# (HanRun HR041087), the MAXREFDES111B# design uses this exact Sumida part number for compliance and performance assurance.

Does the MAXREFDES111B# include soft-start functionality, and how is it implemented?

Yes, the MAXREFDES111B# implements soft-start via capacitor C10 connected to the SS pin of the MAX17498B controller. This configuration programs a 5ms soft-start period, reducing inrush current during power-up and preventing output overshoot. The soft-start timing is directly tied to the internal current source charging C10, and the value of C10 (100nF) was selected to meet the 5ms requirement under worst-case input conditions. MAXREFDES111B#'s soft-start behavior is verified in lab measurements.

What is the maximum output current and overcurrent protection behavior of the MAXREFDES111B#?

The MAXREFDES111B# delivers up to 400mA continuously at 5V, with 20% overrange capability (up to 480mA). Primary-side overcurrent protection is implemented via the MAX17498B's cycle-by-cycle current limit, set to 1.3A peak using resistor R6. Under overload, the design enters hiccup-mode - shutting down, cooling, then restarting - minimizing thermal stress. This behavior is confirmed in transient testing and documented in the MAXREFDES111B# lab reports.

How is output voltage regulation achieved on the MAXREFDES111B#?

Output voltage regulation on the MAXREFDES111B# is achieved using secondary-side optocoupler feedback (U2) and TL431-based shunt regulator (U3), with precision resistors R9/R19/R20 setting the 5V reference. This closed-loop system adjusts duty cycle via the optocoupler's LED current, ensuring ±5% output accuracy across line, load, and temperature. Regulation occurs independently of primary-side components, enabling tight tolerance without direct sensing on the isolated output rail. MAXREFDES111B#'s regulation performance is validated across 0–400mA loads.