Inrush current happens when capacitor is initially charged from 0V to the intended rail voltage.
What should be the effective capacitance to be considered during this charging? -Since the voltage keeps on varying and effective capacitance for a ceramic cap varies with voltage
The same question applies to even RC circuit used to set delay. Say a 3.3V signal passed to RC circuit-> Why we are not considering the dc bias effect of cap while calculating the RC timeconstant?
Inrush current happens when capacitor is initially charged from 0V to the intended rail voltage.
What should be the effective capacitance to be considered during this charging? -Since the voltage keeps on varying and effective capacitance for a ceramic cap varies with voltage
The effective capacitance will be given by the total integrated charge required to get to the target voltage, divided by the target voltage, so somewhere between the unbiased and the fully biassed capacitance.
However, why are you computing the inrush? Usually, inrush is 'bad' in the sense that it's going to blow fuses, or delay power supply startups. In which case, taking a conservative worst case estimate is probably more useful, which means use the larger, unbiased, capacitance for calculation.
The same question applies to even RC circuit used to set delay. Say a 3.3V signal passed to RC circuit-> Why we are not considering the dc bias effect of cap while calculating the RC timeconstant?
If we are setting a delay with an RC, we don't usually use a ceramic capacitor with a nasty voltage coefficient. We could integrate the charge and use the effective capacitance as above, but usually, capacitors with a nasty voltage coefficient also have a nasty temperature coefficient and a lousy initial tolerance as well, preventing us getting a real improvement in accuracy.
If timing is important, use a well-specified capacitor, which generally means a plastic film type, you can get surface mountable ones. There are well-specified ceramics available, but they tend to have fairly small values.
