Other Parts Discussed in Thread: TPS7A88
Hi
My customer has question.
Customer plan to use TPS 7A91 as attached, but there are not any places that are considered to be particularly problem?
Regard
T Kishi
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Hi T,
I agree with Ryan. Replacing a ceramic with a low ESR by a electrolytic with higher ESR only to avoid ringing is no good idea, because this will impair the decoupling performance. Another method of putting an electrolytic cap (snubber) in parallel to the ceramic cap can be helpful in situations where a resistance in series to the choke cannot be allowed because the load current would create a too high voltage drop. But in this case the snubber must be designed very carefully, because only a well dosed ESR will do the trick.
But in your case it's much easier to add a series damping resistance. An example: The BLM18AG601SN1D has a low frequency inductance of about 3.2µH. In your circuit it forms a low pass filter with a 10µF ceramic. As a rule of thumb a series resistance of R>=SQRT(2L/C) = 0.8R would be needed to fully dampen the resonance:
But your BLM18AG601SN1D has already a DC resistance of about 0.22R This allows for certain damping:
If your application can live with this resonance you must not add any series resistance.
Kai