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TPS54560: Capacitor at FB pin (TPS54560)

Part Number: TPS54560


We have used two of this part in one of our PCBs. We used the typical application circuit and we followed all guides in the datasheet as well. We added a 1nF capacitor between the FB pin and ground to have less noise at the output. Amount of load current is small and around 50mA. I am measuring around 100mV ripple with frequency of 12kHz at the output. When I remove the capacitor at the FB pin, the ripple is reduced to nearly half and its frequency is increased to double. We don't have this frequency in our design. Even in no-load condition, we have similar ripples (100mV) at the output.

One of the TI colleague sent me a spreadsheet to do design calculations. I used it to calculate the design value. We have relatively similar values in our design. The problem that I have seen is about adding a capacitor to FB pin. As I mentioned, I am measuring different ripple levels at the output with and without this capacitor. I have checked 2 separate PCBs and they have similar responses.

There isn't any information about capacitance at the FB pin in the datasheet or in the spreadsheet. Really, we expected to have better response from ripple level point of view with adding a capacitor to the FB pin but it seems the pin is very sensitive to the value of the capacitance at the FB pin.

Any advice in this regard?