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# TPS3890: calculation of Cct capacitance

Part Number: TPS3890

Hi Team,

My customer has tried to figure out which capacitor to choose for CT. On page 4 Cctmax=22uF and on page 11 it is CTmax=26uF

However if U calculate tpd(sec) from 0-26uF (see in plot below), tpd goes up to 58sec at Cct=26uF. Can you please advise?

• Hi Jan,

My calculation results in something similar to what the datasheet says.  See below:

tPD(r) = ((26uF * 1.22V) / 1.15uA) + 25us

tPD(r) = 27.58 seconds

26uF is not a standard capacitor value so I would use 22uF.  I think to achieve 30 seconds delay, the the capacitor value will need to be 28.29uF.

Ben

• Hi Ben,

thanks for the reply. Yes you are right. I inserted tPD(r)(nom) as seconds not as us.

Thanks

Jan

• Hi Jan,

If there are no further questions, please close the thread by clicking on "resolved".  Thanks and good luck to you!

Ben