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TPS62821: Can I design with 250uF output capacitance?

Part Number: TPS62821
Other Parts Discussed in Thread: TPS62825, TPS82084


I’m working on a core power supply for a small FPGA and I have a few questions about some parts.

The requirements are:

Vin: 2.8 – 4.5V

Vout: 1.1V +/- 2.5%

Iout: 1 – 2 A

I’m looking at the TPS62821 (1A) and the TPS62825 (2A). Using the FPGA vendors tools I’ve come up with a capacitance requirement of about 250uF, however both of those parts don’t recommend more than 47 – 100uF of output capacitance, or at least suggest that other values should be evaluated carefully. The FPGA vendors tools model the power supply as a voltage source in series with a resistor (1m ohm by default) and an inductor (20nH). They suggest that those values should be adjusted to match the power supply’s datasheet, but I’m not sure how to come up with the correct values. It is possible that with better values for those parameters the capacitance requirements would be reduced. Do you have any idea how to characterize those things?

Both parts also recommend a feed forward capacitor for larger output capacitances. Is it possible to adjust the value of that capacitor to achieve stability with a larger output capacitance? If so, how would I go about doing that?

Thank you,