19-2991; Rev 2; 2/06
IEEE 802.3af PD Interface Controller
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.
Wireless Access Nodes IEEE 802.3af Power Devices
♦ Fully Integrated IEEE 802.3af-Compliant PD
♦ PD Detection and Programmable Classification
♦ Less than 10µA Leakage Current Offset During
♦ Integrated MOSFET For Isolation and Inrush
♦ 90V Absolute Maximum Rating
♦ Gate Output Allows External Control of the
Internal Isolation MOSFET
♦ Programmable Inrush Current Control
♦ Programmable Undervoltage Lockout
♦ Wide UVLO Hysteresis Accommodates Twisted-
Pair Cable Voltage Drop
♦ PGOOD/PGOOD Outputs to Enable Downstream
♦ -40°C to +85°C Operating Temperature Range
MAX5940AESA -40°C to +85°C
MAX5940BESA -40°C to +85°C
MAX5940CESA -40°C to +85°C
MAX5940DESA -40°C to +85°C
Pin Configurations appear at end of data sheet.
Typical Operating Circuits
MAX5940C PGOOD 6
Typical Operating Circuits continued at end of data sheet.
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