SLVSB97E July 2012 – January 2018 TPS23751 , TPS23752
PRODUCTION DATA.
IEEE 802.3at has a startup current and time limitation, providing type 2 PSE compatibility for type 1 PDs. A type 2 PSE limits output current to between 400 mA and 450 mA for up to 75 ms after power-up (applying “48 V” to the PI) in order to mirror type 1 PSE functionality. The type 2 PSE supports higher output current after 75 ms. The TPS23751 and TPS23752 implement a 140 mA inrush current, which is compatible with all PSE types. A high-power PD must limit its converter startup peak current. The operational current cannot exceed 400 mA for a period of 80 ms or longer. The TPS23751 and TPS23752 internal soft-start permits control of the converter startup, however the application circuits must assure that their power draw does not cause the PD to exceed the current and time limitation. This requirement implicitly requires some form of powering down sections of the application circuits. T2P becomes valid within tT2P after switching starts, or if an adapter is plugged in while the PD is operating from a PSE.