SLUSBX9I March 2014 – July 2019 TPS23861
The TPS23861 provides three levels of overcurrent protection. During the tSTART period immediately following power up, inrush current protection is provided as described in Inrush Protection. This protection allows the input capacitance of the PD to charge to the full input voltage on the power interface while ensuring the pass FET remains within its safe operating area.
Following the end of the tSTART period a two-tiered current-limit protection scheme is applied to the ports. The first level (i.e., lower current) is the ICUT current limit. The ICUT current-limit threshold is set using the ICUTnm CONFIG registers and includes a timeout, tOVLD, set using TICUT field in the TIMING CONFIGURATION register. When the TICUT timer times out because the ICUT current threshold is exceeded, the port is powered off, and the ICUTn bit in the FAULT EVENT register is set with the option of asserting an interrupt. This delay in powering down the port provides protection against spurious power downs during moderate load transients. See ICUT Current Limit.
The second level of powered-on current-limiting protection is the ILIM current limit. The ILIM current limit is a hard limit. That is, hardware protection including voltage foldback is imposed when the ILIM current threshold is reached. This second level of protection is invoked in the event of extreme overload or short circuit. The ILIM current-limit value is set using the POEPn bits in the PoE Plus register. Also, when the ILIM value is reached, the ILIM timer is started. When the ILIM timer times out, the port is powered off and the ILIMn bit in the Start/ILIM Event Register is set with the option of asserting an interrupt. See Foldback Protection (ILIM).