The MAX5941A/MAX5941B 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 powergood status outputs. The MAX5941A/MAX5941B also integrate all the building blocks necessary for implementing DC-DC fixedfrequency isolated power supplies. These devices are a current-mode controller with an integrated high startup circuit suitable for isolated telecom/industrial voltagerange 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 MAX5941A allows an 85% operating duty cycle and can be used to implement flyback converters. The MAX5941B limits the operating duty cycle to less than 50% and can be used in single-ended forward converters. The MAX5941A/MAX5941B are designed to work with or without an external diode bridge in front of the PD. The MAX5941A/MAX5941B are available in 16-pin SO packages.