Rainbow Electronics MAX5940B - Manual

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
V EE
GATE
RCLASS
PGOOD
DC-DC CONVERTER
GND
-48V
R CL
*OPTIONAL.
GND
V+
LOAD
V REG
D1*
OUT
2
3
4 5
6
8
C OUT
C GATE
R DISC
25.5k Ω
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.