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TPS62090: Cff selection

Mark Pieper
Expert 4640 points
Part Number: TPS62090
Other Parts Discussed in Thread: TPS62823, TPS62085, TPS62088

I see that the EVM schematic includes a Cff but there is no mention in the DS or users guide about it. My current design (3.3V to 1.0V) does not include it.

I'm interested in improving the transient response of the circuit. Is there any advantage of adding a Cff, possibly with a low frequency cutoff, in improving the transient response in this DCS converter? My stability looks good, so I don't think I need a Cff for phase margin improvement.

Thanks,

Mark

  • 0
    TI__Guru**** 150770 points
    Hi Mark,

    A Cff doesn't typically help much with these devices. First, your Vout is very close to the FB pin voltage so there is not much gain there. Second, the Cff only helps when the loop BW is rather low. See www.ti.com/.../slva466a.pdf

    As this is an older device, I would recommend newer devices. TPS62085 is smaller and has better transient response due to its smaller inductance. TPS62823 and TPS62088 are brand new and very small. Their transient response is usually a little worse than TPS62085 due to their lack of a VOS pin.