SLVSE57C June 2017 – April 2018 TPS2595
Some applications require the output capacitor to be discharged quickly when the eFuse is turned off. This prevents any unpredictable behavior from the downstream devices as the capacitor discharges slowly. The TPS2595x5 device provides a Quick Output Discharge feature that can be enabled by connecting OUT pin to QOD pin. An internal FET provides a fast discharge path for the output capacitor resulting in the OUT voltage falling to 0 V in a short time. The FET initially operates in saturation region and provides a constant current discharge. After the FET enters linear region, it offers a discharge path similar to a resistor.
It is possible to model this as a simple equivalent resistance, which would discharge a given capacitor charged to a given voltage in the same time as the overall discharge circuit. This parameter is specified as the effective QOD resistance RQOD for the device. It takes a time equivalent to 5 time constants (τ = R × C) to discharge a capacitor by 99.3%. For example, with an effective QOD resistance of 19 Ω, the time taken to discharge a 100-µF capacitor from 5 V to 35 mV can be calculated as in Equation 5.