The TPS25985x responds to output overcurrent conditions during start-up by actively limiting the current. The device constantly senses the current flowing through each one (I_DEVICE) and provides an analog current output (I_ILIM) on the ILIM pin, which in turn produces a proportional voltage (V_ILIM) across the ILIM pin resistor (R_ILIM) as per Equation 9.

The overcurrent condition is detected by comparing this voltage against a threshold which is a scaled voltage (CLREF_SAT) derived from the reference voltage (V_IREF) on the IREF pin as presented in Equation 10.

1. In the standalone mode of operation, the internal current source interacts with the external IREF pin resistor (R_IREF) to generate the reference voltage as shown in Equation 11.

   Equation 11. $V_{IREF}=I_{IREF}\times R_{IREF}$

2. In a primary and secondary configuration, the primary eFuse or controller drives the voltage on the IREF pin to provide an external reference (V_IREF).

The active current limit (I_LIM) threshold during start-up can be calculated using Equation 12.

When the load current during start-up exceeds I_LIM, the device tries to regulate and hold the load current at I_LIM.

During current regulation, the output voltage drops, resulting in increased device power dissipation across the FET. If the device internal temperature (T_J) exceeds the thermal shutdown threshold (TSD), the FET is turned off. After the part shuts down due to a TSD fault, it either stays latched off (TPS259850 variants) or restarts automatically after a fixed delay (TPS259851 variants). See Overtemperature protection section for more details on device response to overtemperature.