General Description

The MAX5942A/MAX5942B integrate a complete power

IC for powered devices (PD) in a power-over-ethernet

(PoE) system. The MAX5942A/MAX5942B provide a PD

interface and a compact DC-DC PWM controller suitable

for flyback and forward converters in either isolated or

nonisolated designs.

The MAX5942A/MAX5942B PD interface complies with

the IEEE 802.3af standard, providing the PD with a detec-

tion signature, a classification signature, and an integrat-

ed isolation switch with programmable inrush current

control. These devices also feature power-mode under-

voltage lockout (UVLO) with wide hysteresis and power-

good status outputs.

The MAX5942A/MAX5942B also integrate all the build-

ing blocks necessary for implementing DC-DC fixed-

frequency isolated power supplies. This device is a

current-mode controller with an integrated high startup

circuit suitable for isolated telecom/industrial voltage

range power supplies. A high-voltage startup circuit

allows the PWM controller to draw power directly from the

18V to 67V input supply during startup. The switching

frequency is internally trimmed to 275kHz ±10%, thus

reducing magnetics and filter components. The

MAX59412A allows an 85% operating duty cycle and can

be used to implement flyback converters. The MAX5942B

limits the operating duty cycle to less than 50% and can

be used in single-ended forward converters. The

MAX5942A/MAX5942B are designed to work with or with-

out an external diode bridge in front of the PD.

The MAX5942A/MAX5942B are available in 16-pin SO

packages.

Applications

IP Phones

Wireless Access Nodes

Internet Appliances

Computer Telephony

Security Cameras

Power Devices in Power-Over-Ethernet/

Power-Over-MDI

Features

o Powered Device Interface

Fully Integrated IEEE 802.3af-Compliant PD

Interface

PD Detection and Programmable Classification

Signatures

Less than 10µA Leakage Current Offset During

Detection

Integrated MOSFET for Isolation and Inrush

Current Limiting

Gate Output Allows External Control of the

Internal Isolation FET

Programmable Inrush Current Control/ULVO

PGOOD/PGOOD Outputs Enable PWM

Controller

o PWM Controller

Wide Input Range: 18V to 67V

Isolated (Without Optocoupler) or Nonisolated

Power Supply

Current-Mode Control

Leading-Edge Blanking

Internally Trimmed 275kHz ±10% Oscillator

Soft-Start

IEEE 802.3af Power-Over-Ethernet

Interface/PWM Controller for Power Devices

________________________________________________________________ Maxim Integrated Products

1

Ordering Information

19-3024; Rev 0; 10/03

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

PART

TEMP RANGE

PIN-

PACKAGE

MAX DUTY

CYCLE (%)

MAX5942AESE*

-40°C to +85°C

16 SO

85

MAX5942ACSE

0°C to +70°C

16 SO

85

MAX5942BESE*

-40°C to +85°C

16 SO

50

MAX5942BCSE

0°C to +70°C

16 SO

50

Typical Operating Circuit appears at end of data sheet.

*Future product—contact factory for availability.

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

V+

NDRV

V-

CS

GND

PGOOD

PGOOD

OUT

TOP VIEW

MAX5942A

MAX5942B

SO

FB

RCL

SS_SHDN

ULVO

GATE

Pin Configuration