The PD70101 is an integrated Powered Device Interface and PWM controllers for a DC-DC converter used in IEEE802.3af applications. The PD70101 can be used for IEEE802.3af or IEEE802.3at Type 1 applications. This device has a number of features designed to improve efficiency and reliability: Detection and Classification: The front end interface includes detection and classification circuitry. The detection signature resistor is disconnected upon completion of the detection phase. The system then begins the classification phase. Classification can be configured for Classes 0 to 4 via an external resistor. Capacitor: A current limited internal MOSFET switch charges the input capacitor of the DC-DC converter. This capacitor is discharged in a timely manner when the input power is removed. Gate drivers: The PWM DC-DC controller has two built-in gate drivers designed to swing between VCC and GND. These 2 out-of-phase driver stages can be configured for synchronous rectification or active clamp.Peak current mode control: The DC-DC converter employs peak current mode control for better line and load step response. The switching frequency can be set from 100kHz to 500kHz, enabling a size and efficiency trade off. Maximum duty cycle is limited to 50% to reduce the power MOSFET switch voltage to two times the input voltage; a 150V rated MOSFET can be used for the primary side switch. The secondary synchronous MOSFET voltage rating depends on the output voltage and can be higher or lower than the primary side MOSFET switch. Soft-start circuit: The device includes a soft-start circuit to control the output voltage rise time (user settable) at start up, and to limit the inrush current. An integrated startup bias circuit powers the DC-DC controller, until the device starts up by the voltage generated by the bootstrap circuit. Low Voltage Protection Warning and Monitoring: Dual Under Voltage Lock Out (UVLO), which monitors both the PoE Port Input Voltage and VCC, ensures reliable operation during any system disturbances. The PoE port UVLO has a programmable threshold and hysteresis to enable tailoring to the desired turn on and turn off voltage. An internal current sense amplifier with a Kelvin connection allows the use of an extremely low resistor to measure the current sense threshold voltage (200 mV) which optimizes efficiency. Low Power Mode operation: provided to improve efficiency under light loads such as when the PD is in standby. The user can define at what power level the unit enters low power mode by means of a single resistor value.