The MAX5953A/MAX5953B/MAX5953C/MAX5953D
integrate a complete power IC solution for Powered
Devices (PD) in a Power-Over-Ethernet (PoE) system, in
compliance with the IEEE 802.3af standard. The
MAX5953A/MAX5953B/MAX5953C/MAX5953D provide
the PD with a detection signature, a classification signature,
and an integrated isolation switch with programmable
inrush current control. These devices also
integrate a voltage-mode PWM controller with two
power MOSFETs connected in a two-switch voltage-clamped
DC-DC converter configuration.
An integrated MOSFET provides PD isolation during
detection and classification. All devices guarantee a
leakage current offset of less than 10µA during the
detection phase. A programmable current limit prevents
high inrush current during power-on. The devices
feature power-mode undervoltage lockout (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 MAX5953A/MAX5953C
have an adjustable UVLO threshold with the default
value compliant to the 802.3af standard, while the
MAX5953B/MAX5953D have a lower and fixed UVLO
threshold compatible with some legacy pre-802.3af
power-sourcing equipment (PSE) devices.
The DC-DC converters are operable in either forward or
flyback configurations with a wide input voltage range
from 11V to 76V and up to 15W of output power. The
voltage-clamped power topology enables full recovery
of stored magnetizing and leakage inductive energy for
enhanced efficiency and reliability. When using the
high-side MOSFET, the controller can be configured as
a buck converter. A look-ahead signal for driving secondary-side synchronous rectifiers can be used to
increase efficiency. A wide array of protection features
include UVLO, over-temperature shutdown, and short-circuit
protection with hiccup current limit for enhanced
performance and reliability. Operation up to 500kHz
allows for smaller external magnetics and capacitors.
The MAX5953A/MAX5953B/MAX5953C/MAX5953D are
available in a high-power (2.22W), 7mm x 7mm thermally
enhanced thin QFN package.
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