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General Description

The MAX5940A/MAX5940B provide complete interface

function for a powered device (PD) to comply with the

IEEE 802.3af standard in a power-over-ethernet system.

MAX5940A/MAX5940B provide the PD with a detection

signature, a classification signature, and an integrated

isolation switch with programmable inrush current con-

trol. These devices also feature power-mode undervolt-

age lockout (UVLO) with wide hysteresis, and

power-good outputs.

An integrated MOSFET provides PD isolation during

detection and classification. The MAX5940A/MAX5940B

guarantee a leakage current offset of less than 10µA dur-

ing the detection phase. A programmable current limit

prevents high inrush current during power-on. The device

features power-mode UVLO with wide hysteresis and

long deglitch time to compensate for twisted-pair cable

resistive drop and to assure glitch-free transition between

detection, classification, and power-on/-off phases.

The MAX5940A provides an active-high (PGOOD) open-

drain output and a fixed UVLO threshold. The MAX5940B

provides both active-high (PGOOD) and active-low

(PGOOD) outputs and has an adjustable UVLO threshold

with the default value compliant to the 802.3af standard.

The MAX5940A/MAX5940B are designed to work with or

without an external diode bridge.

The MAX5940A/MAX5940B are available in 8-pin SO

packages and are rated over the extended temperature

range of -40°C to +85°C.

Applications

IP Phones Security Cameras

Wireless Access Nodes IEEE 802.3af Power Devices

Computer Telephony

Features

♦ 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 MOSFET

♦ Programmable Inrush Current Control

♦ Programmable Undervoltage Lockout

(MAX5940B Only)

♦ Wide UVLO Hysteresis Accommodates Twisted-

Pair Cable Voltage Drop

♦ PGOOD/PGOOD Outputs to Enable Downstream

DC-DC Converters

♦ -40°C to +85°C Operating Temperature Range

MAX5940A/MAX5940B

IEEE 802.3af PD Interface Controller

For Power-Over-Ethernet

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

60V

68nF

GND

GATE

RCLASS

PGOOD

DC-DC CONVERTER

GND

-48V

*OPTIONAL.

GND

V+

LOAD

REG

D1*

OUT

GATE

DISC

25.5kΩ

SS_SHDN

MAX5014

MAX5940A

D2*

Typical Operating Circuits

19-2991; 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.

Pin Configurations appear at end of data sheet.

PART TEMP RANGE

PIN-

PACKAGE

UVLO

MAX5940AESA -40°C to +85°C 8 SO Fixed

MAX5940BESA -40°C to +85°C 8 SO Adjustable

Typical Operating Circuits continued at end of data sheet.

1 2 3 4 5 6 ... 14 15

Indice de contenidos

Pagina 1 - For Power-Over-Ethernet

General DescriptionThe MAX5940A/MAX5940B provide complete interfacefunction for a powered device (PD) to comply with theIEEE 802.3af standard in a pow

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet10 ______________________________________________________________________

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet_________________________________________________________________________

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet12 ______________________________________________________________________

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet_________________________________________________________________________

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet14 ______________________________________________________________________

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-EthernetMaxim cannot assume responsibility for use of any circuitry other than ci

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet2 _______________________________________________________________________

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet_________________________________________________________________________

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet4 _______________________________________________________________________

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MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet_________________________________________________________________________

Pagina 12

MAX5940A/MAX5940BIEEE 802.3af PD Interface Controller For Power-Over-Ethernet6 _______________________________________________________________________

Pagina 13

The PSE determines the class of a PD by applying a volt-age at the PD input and measures the current sourcedout of the PSE. When the PSE applies a vol

Pagina 14

MAX5940A/MAX5940BTo adjust the UVLO threshold (MAX5940B only), con-nect an external resistor-divider from GND to UVLOand from UVLO to VEE. Use the fol

Pagina 15

Inrush Current LimitThe MAX5940A/MAX5940B charge the gate of theinternal MOSFET with a constant current source (10µA,typ). The drain-to-gate capacitan

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