Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers

Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers with Adjustable Frequency from 100kHz to 600kHz

Please check latest availability status for a specific part variant.


The MAX5974_ provide control for wide-input-voltage, active-clamped, current-mode PWM, forward converters in Power-over-Ethernet (PoE) powered device (PD) applications. The MAX5974A/MAX5974C are well-suited for universal or telecom input range, while the MAX5974B/MAX5974D also accommodate low input voltage down to 10.5V.

The devices include several features to enhance supply efficiency. The AUX driver recycles magnetizing current instead of wasting it in a dissipative clamp circuit. Programmable dead time between the AUX and main driver allows for zero-voltage switching (ZVS). Under light-load conditions, the devices reduce the switching frequency (frequency foldback) to reduce switching losses.

The MAX5974A/MAX5974B feature unique circuitry to achieve output regulation without using an optocoupler, while the MAX5974C/MAX5974D utilize the traditional optocoupler feedback method. An internal error amplifier with a 1% reference is very useful in nonisolated design, eliminating the need for an external shunt regulator.

The devices feature a unique feed-forward maximum duty-cycle clamp that makes the maximum clamp voltage during transient conditions independent of the line voltage, allowing the use of a power MOSFET with lower breakdown voltage. The programmable frequency dithering feature provides low-EMI, spread-spectrum operation.

The MAX5974_ are available in 16-pin TQFN-EP packages and are rated for operation over the -40°C to +85°C temperature range.

MAX5974A, MAX5974B: Typical Application Circuit MAX5974A, MAX5974B: Typical Application Circuit Enlarge+

Key Features

  • Peak Current-Mode Control, Active-Clamped Forward PWM Controller
  • Regulation Without Optocoupler (MAX5974A/MAX5974B)
  • Internal 1% Error Amplifier
  • 100kHz to 600kHz Programmable ±8% Switching Frequency, Synchronization Up to 1.2MHz
  • Programmable Frequency Dithering for Low-EMI, Spread-Spectrum Operation
  • Programmable Dead Time, PWM Soft-Start, Current Slope Compensation
  • Programmable Feed-Forward Maximum Duty-Cycle Clamp, 80% Maximum Limit
  • Frequency Foldback for High-Efficiency Light-Load Operation
  • Internal Bootstrap UVLO with Large Hysteresis
  • 100µA (typ) Startup Supply Current
  • Fast Cycle-by-Cycle Peak Current-Limit, 35ns Typical Propagation Delay
  • 115ns Current-Sense Internal Leading-Edge Blanking
  • Output Short-Circuit Protection with Hiccup Mode
  • Reverse Current Limit to Prevent Transformer Saturation Due to Reverse Current
  • Internal 18V Zener Clamp on Supply Input
  • 3mm x 3mm, Lead-Free, 16-Pin TQFN-EP


  • Active-Clamped Forward DC-DC Converters
  • High-Power PD (Beyond the 802.3af/at Standard)
  • IP Phones
  • PoE IEEE® 802.3af/at Powered Devices
  • Security Cameras
  • Wireless Access Nodes

Pricing Notes:
This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.

MAX5974AEVKIT: Evaluation Kit for the MAX5974A
MAX5974CEVKIT: Evaluation Kit for the MAX5974C
Product Reliability Reports: MAX5974D.pdf 
Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C   Material Composition  

Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

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