Datasheet

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General Description

The MAX5940A/MAX5940B/MAX5940C/MAX5940D pro-

vide complete interface function for a powered device

(PD) to comply with the IEEE 802.3af standard in a

power-over-ethernet system. MAX5940A/MAX5940B/

MAX5940C/MAX5940D provide the PD with a detection

signature, a classification signature, and an integrated

isolation switch with programmable inrush current control.

These devices also feature power-mode undervoltage

lockout (UVLO) with wide hysteresis and power-

good outputs. The MAX5940A/MAX5940B are available

with an absolute maximum rating of 80V and the

MAX5940C/MAX5940D are rated for an absolute maxi-

mum rating of 90V.

An integrated MOSFET provides PD isolation during

detection and classification. All devices guarantee a leak-

age current offset of less than 10µA during 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, classifica-

tion, and power-on/-off phases.

The MAX5940A/MAX5940C provide an active-high

(PGOOD) open-drain output and a fixed UVLO threshold.

The MAX5940B/MAX5940D provide both active-high

(PGOOD) and active-low (PGOOD) outputs and have an

adjustable UVLO threshold with the default value compli-

ant to the 802.3af standard. All devices are designed to

work with or without an external diode bridge.

The MAX5940A/MAX5940B/MAX5940C/MAX5940D 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

♦ 90V Absolute Maximum Rating

(MAX5940C/MAX5940D)

♦ Gate Output Allows External Control of the

Internal Isolation MOSFET

♦ Programmable Inrush Current Control

♦ Programmable Undervoltage Lockout

(MAX5940B/MAX5940D 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/MAX5940C/MAX5940D

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

MAX5940C

D2*

Typical Operating Circuits

19-2991; Rev 2; 2/06

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.

EVALUATION KIT

AVAILABLE

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

MAX5940CESA

-40°C to +85°C

8 SO Fixed

MAX5940DESA

-40°C to +85°C

8 SO

Adjustable

Typical Operating Circuits continued at end of data sheet.

Summary of content (15 pages)

PAGE 1
9-2991; Rev 2; 2/06 KIT ATION EVALU LE B A IL A AV IEEE 802.3af PD Interface Controller For Power-Over-Ethernet Features The MAX5940A/MAX5940B/MAX5940C/MAX5940D 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/ MAX5940C/MAX5940D provide the PD with a detection signature, a classification signature, and an integrated isolation switch with programmable inrush current control.
PAGE 2
MAX5940A/MAX5940B/MAX5940C/MAX5940D IEEE 802.3af PD Interface Controller For Power-Over-Ethernet ABSOLUTE MAXIMUM RATINGS GND, RCLASS to VEE .....................................................70mA UVLO, PGOOD, PGOOD to VEE .....................................20mA GATE to VEE ....................................................................80mA Continuous Power Dissipation (TA = +70°C) 8-Pin SO (derate 5.9mW/°C above +70°C)..................470mW Operating Temperature Range ...........................
PAGE 3
IEEE 802.3af PD Interface Controller For Power-Over-Ethernet (VIN = (GND - VEE) = 48V, GATE = PGOOD = PGOOD = OUT = OPEN, UVLO = VEE, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to VEE, unless otherwise noted.
PAGE 4
IIN dRi ≅ 1V (VINi + 1 - VINi) = (IINi + 1 - IINi) (IINi + 1 - IINi) IOFFSET ≅ IINi - VINi dRi IINi + 1 dRi IINi IOFFSET VINi 1V VINi + 1 VIN Figure1. Effective Differential Input Resistance/Offset Current Typical Operating Characteristics (VIN = (GND - VEE) = 48V, GATE = PGOOD = PGOOD = OUT = OPEN, UVLO = VEE (MAX5940B), TA = -40°C to +85°C. Typical values are at TA = +25°C. All voltages are referenced to VEE, unless otherwise noted.) 0.3 IIN + IRDISC 0.2 0.
PAGE 5
IEEE 802.3af PD Interface Controller For Power-Over-Ethernet (VIN = (GND - VEE) = 48V, GATE = PGOOD = PGOOD = OUT = OPEN, UVLO = VEE (MAX5940B), TA = -40°C to +85°C. Typical values are at TA = +25°C. All voltages are referenced to VEE, unless otherwise noted.) OUT LEAKAGE CURRENT vs. TEMPERATURE PGOOD OUTPUT LOW VOLTAGE vs.
PAGE 6
MAX5940A/MAX5940B/MAX5940C/MAX5940D IEEE 802.3af PD Interface Controller For Power-Over-Ethernet Pin Description PIN MAX5940A/ MAX5940B/ MAX5940C MAX5940D 1, 7 — NAME N.C. — 1 UVLO 2 2 RCLASS FUNCTION No Connection. Not internally connected. Undervoltage Lockout Programming Input for Power Mode. When UVLO is above its threshold, the device enters power mode. Connect UVLO to VEE to use the default undervoltage lockout threshold.
PAGE 7
IEEE 802.3af PD Interface Controller For Power-Over-Ethernet CLASS USAGE RCL (Ω) MAXIMUM POWER USED BY PD (W) 0 Default 10k 0.44 to 12.95 1 Optional 732 0.44 to 3.84 2 Optional 392 3.84 to 6.49 3 Optional 255 6.49 to 12.95 4 Not Allowed 178 Reserved* *Class 4 reserved for future use. Table 2. Setting Classification Current CLASS CURRENT SEEN AT VIN (mA) IEEE 802.3af PD CLASSIFICATION CURRENT SPECIFICATION (mA) CLASS RCL (Ω) VIN* (V) MIN MAX MIN 0 10k 12.
PAGE 8
MAX5940A/MAX5940B/MAX5940C/MAX5940D IEEE 802.3af PD Interface Controller For Power-Over-Ethernet GND 2.46V UVLO REF EN GND CLASSIFICATION 6.8V RCLASS R1 (PGOOD) MAX5940B MAX5940D Q4 R2 20% R3 VGATE 1.2V, REF EN (UVLO) PGOOD 5V, REF Q3 OUT Q2 200mV GATE Q1 VEE ( ) MAX5940B. Figure 2. Block Diagram To adjust the UVLO threshold (MAX5940B/MAX5940D only), connect an external resistor-divider from GND to UVLO and from UVLO to VEE.
PAGE 9
IEEE 802.3af PD Interface Controller For Power-Over-Ethernet IINRUSH = IG x COUT CGATE PGOOD/PGOOD Outputs (MAX5940A/MAX5940C only) PGOOD is an open-drain, active-high logic output. PGOOD goes high impedance when VOUT is within 1.2V of VEE and when GATE is 5V above VEE. Otherwise, PGOOD is pulled to VOUT (given that VOUT is at least 5V below GND). Connect PGOOD to the ON pin of a downstream DC-DC converter. Connect a 100kΩ pullup resistor from PGOOD to GND if needed.
PAGE 10
IEEE 802.3af PD Interface Controller For Power-Over-Ethernet MAX5940A/MAX5940B/MAX5940C/MAX5940D Typical Application Circuits Application Circuit 1 POWER-OVER SIGNAL PAIRS VREG RX 3 6 1 PHY 2 GND + + - - RJ-45 4 TX 5 7 -48V 8 POWER-OVER SPAIR PAIRS DC-DC CONVERTER GND V+ RDISC 25.
PAGE 11
IEEE 802.3af PD Interface Controller For Power-Over-Ethernet GATE is pulled low to pinch off the power-over-ethernet. The wall adapter power pollutes the discovery signature, preventing PSE from detecting this PD. Application Circuit 2 Diode D1 prevents the power-over-ethernet to back drive the wall adapter. Whenever the wall adapter power is greater than (VD3 + approximately 2V), the DC-DC CONVERTER V+ GND 1 RDISC 25.
PAGE 12
MAX5940A/MAX5940B/MAX5940C/MAX5940D IEEE 802.3af PD Interface Controller For Power-Over-Ethernet Typical Application Circuits (continued) Application Circuit 3 R4 provides the 10mA minimum power maintenance signature to keep the power-over-ethernet from disconnecting. D2 prevents the wall adapter power from polluting the discovery and classification signatures. The optional DC-DC CONVERTER D2 V+ GND 1 RDISC 25.
PAGE 13
IEEE 802.3af PD Interface Controller For Power-Over-Ethernet Application Circuit 4 fication signatures. If the power-over-ethernet comes up first, it powers the load until taken over by a wall adapter with higher output voltage. If the wall adapter supply comes up first, it provides power to the load and pollute the discovery and classi- DC-DC CONVERTER V+ GND 1 RDISC 25.
PAGE 14
IEEE 802.3af PD Interface Controller For Power-Over-Ethernet MAX5940A/MAX5940B/MAX5940C/MAX5940D Typical Operating Circuits (continued) D1* DC-DC CONVERTER GND RDISC 25.5kΩ V+ R1** 1 60V 68nF 2 RCL R2** D2* 3 UVLO RCLASS GATE 4 -48V VEE GND PGOOD 8 MAX5014 COUT 7 GND SS_SHDN VREG LOAD MAX5940B 6 PGOOD MAX5940D OUT 5 CGATE *OPTIONAL. **R1 AND R2 ARE OPTIONAL AND WHEN USED, THEY MUST TOTAL 25.5kΩ AND REPLACE THE 25.5kΩ RESISTOR.
PAGE 15
IEEE 802.3af PD Interface Controller For Power-Over-Ethernet N E H INCHES MILLIMETERS MAX MIN 0.069 0.053 0.010 0.004 0.014 0.019 0.007 0.010 0.050 BSC 0.150 0.157 0.228 0.244 0.016 0.050 MAX MIN 1.35 1.75 0.10 0.25 0.35 0.49 0.25 0.19 1.27 BSC 3.80 4.00 5.80 6.20 0.40 SOICN .EPS DIM A A1 B C e E H L 1.27 VARIATIONS: 1 INCHES TOP VIEW DIM D D D MIN 0.189 0.337 0.386 MAX 0.197 0.344 0.394 MILLIMETERS MIN 4.80 8.55 9.80 MAX 5.00 8.75 10.