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

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

Product Details

Key Features

Applications/Uses

Parametric specs for Powered Devices
PWM Yes
Switching Frequency (kHz) 600
UVLO Threshold (V) 8.4
Package/Pins TQFN/16
Oper. Temp. (°C) -40 to +85
Budgetary
Price (See Notes)
2.05
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Simplified Block Diagram

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Parameters

Parametric specs for Powered Devices
PWM Yes
Switching Frequency (kHz) 600
UVLO Threshold (V) 8.4
Package/Pins TQFN/16
Oper. Temp. (°C) -40 to +85
Budgetary
Price (See Notes)
2.05

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

Applications/Uses

  • 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

Description

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 and -40°C to +125°C temperature ranges.

Simplified Block Diagram

MAX5974A, MAX5974B: Typical Application Circuit MAX5974A, MAX5974B: Typical Application Circuit Zoom icon

Support & Training

Search our knowledge base for answers to your technical questions.

Filtered Search

Our dedicated team of Applications Engineers are also available to answer your technical questions. Visit our support portal .