ZHCSI09S June 2010 – August 2018 TPS65911
Because of the nature of the switching controller with a pulsating input current, a low ESR input capacitor is required for the best input-voltage filtering and also to minimize the interference with other circuits caused by high input-voltage spikes. For the controller, a typical 1-μF capacitor can be used for the V5IN pin to support the transients on the driver. For the FET input, 40 μF of input capacitance is recommended for most applications. To achieve the low ESR requirement, a ceramic capacitor is recommended. However, the voltage rating and DC-bias characteristic of ceramic capacitors must be considered. For better input-voltage filtering, the input capacitor can be increased without any limit. TI recommends placing a ceramic capacitor as near as possible to the FET across the respective VSYS and PGND pins of the FETs.
Use the correct value for the ceramic capacitor capacitance after derating to achieve the recommended input capacitance.