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TPS3808: Maximum allowable delay time?

Part Number: TPS3808
Other Parts Discussed in Thread: TPS37, TPS3760, TPS38

Hello

The datasheet says that the delay can be adjusted  from 1.25 ms to 10 s.

What happens when I put a C_T capacitor that exceeds C_T=175*10=1.75uF?

From a different question/answer in this forum, I know that 14s is possible. (2.45uF)

But what happens if I put e.g. 4uF? 

Will the circuit still work as intended?

Will the delay be capped at 14s?

Will the delay still increase with increasing capacitance, but with higher tolerance on the delay?

Or is it possible that the the chip will never de-assert \RESET or even exhibit a delay shorter than 14s?

I am asking because of the following:

For my application it is important, that the delay is not shorter than e.g. 10s.

But since the time delay of the TPS3808 is apparently only accurate up to  +/-30%, I would need to have a nominal delay of 14.3s, such that 0.7*14.3s>10s.

And 14.3s is outside of the specifications/datasheet.

Thanks for the support!!

Manuel

  • Hello Manuel,

    While it might be possible to use a larger capacitor to get a longer delay time, it is not recommended to use values outside of the datasheet. The delay time could become unpredictable and the delay time would vary with long capacitor charge and discharge times in response to voltage faults. For example, if there is a short duration between voltage faults, the large capacitor may not have enough time to discharge after the first fault which would lead to a much shorter delay after the second fault. 

    The TPS38, TPS37, and TPS3760 should work for your application. They have a 12.8s recommended adjustable reset time delay but can use a larger capacitor. Page 21 in the TPS37 datasheet explains how to use a larger reset delay capacitor. 

    Best,

    Walter