The MAX5942A/MAX5942B integrate a complete power
IC for powered devices (PD) in a power-over-ethernet
(PoE) system. The MAX5942A/MAX5942B provide a PD
interface and a compact DC-DC PWM controller suitable
for flyback and forward converters in either isolated or
nonisolated designs.
The MAX5942A/MAX5942B PD interface complies with
the IEEE™ 802.3af standard, providing 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 status outputs.
The MAX5942A/MAX5942B also integrate all the building
blocks necessary for implementing DC-DC fixed-frequency
isolated power supplies. This device is a
current-mode controller with an integrated high startup
circuit suitable for isolated telecom/industrial voltage
range power supplies. A high-voltage startup circuit
allows the PWM controller to draw power directly from the
18V to 67V input supply during startup. The switching
frequency is internally trimmed to 275kHz ±10%, thus
reducing magnetics and filter components. The
MAX5942A allows an 85% operating duty cycle and can
be used to implement flyback converters. The MAX5942B
limits the operating duty cycle to less than 50% and can
be used in single-ended forward converters. The
MAX5942A/MAX5942B are designed to work with or without
an external diode bridge in front of the PD.
The MAX5942A/MAX5942B are available in 16-pin SO
packages.
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