TPS54A20: Unable to drive the load

Hi,

Using a 2 layer board for this device is not recommended, ideally you want to use a 4 layer board to have internal layers isolated for ground planes that shield FB from other high noise traces. It is much harder to keep low noise on a 2 layer board. In addition, having a 2 layer board can have limited copper and therefore result in insufficient heat dissipation which can lead to thermal shutdown. You mentioned that the only difference is between our EVM and your 2 layer board is essentially layout which points at that been the issue for your fluctuating voltage, most likely you have some noise related issue occurring due to the lack of ground insulation.

A far as your question on series caps, this is for the internal capacitors "CT" located between source of HS FET and drain of LS FET. Threshold for the voltage monitor is between 35% and 65% relative to VIN voltage and PGND, anything outside that will trigger a fault which will shutdown the device and go onto hiccup mode, you can monitor fault through PGOOD (if triggered will go low).