TPS7A25: Feedback resistor

Hi Michiaki,

The FB resistive values can take on a range of values. In this datasheet section 8.2.2.2 goes through the justification for selecting these sizes. The first step is setting an upper bound on the values, because of the leakage current going through the pin, having resistors that are oversized, can cause overvoltage to occur, so the leakage current defines an absolute upper bound on the values. Once this is defined, you pick resistive values that satisfy this definition. The lower the value that you set for the feedback network, the more current you develop. Selecting values near the upper bound minimizes current through the feedback network, allowing more current to flow to the load. It is not a problem if they want to use kohm resistive values, they just have to know that this will draw more current away from their load, and if operating near current limit, can cause the part to not be able to source the current required for both the load and the feedback network.

So by sizing up these values to near the upper limit, the example is allowing maximum current to flow into the load if needed.

Regards,

John