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TPS3808: Reset delay time

Part Number: TPS3808
Other Parts Discussed in Thread: TPS3890

Hi,

I have questions about setting the reset delay time.

When CT=100pF,in the data sheet switching characteristics, td is 1.25 ms(TYP).

The calculation result of the equation is 1.071 ms.

Delay = 100×10^(-3)/175 + 0.5×10^(-3) = 1.071 ms
Q1.What is the difference?

I would like to set td for at least 1.2 seconds using a 330nF capacitor.
Q2.What is the maximum / minimum value of td in this case?

Best regards,
Seishin

  • Seishin,

    The equation is just an approximation. In real life, the capacitor has tolerance, and the internal current source along with the charging threshold can vary slightly. According to the datasheet Table 7.6, to get a delay of 1.2 seconds (0.7 seconds MIN, 1.7 seconds MAX) you should use 180 nF. The calculation comes out to ~209 nF so anything between 180nF and 220nF should put you in the 1.2 second range.

    If you need a tighter tolerance on the delay accuracy, try TPS3890. This device has better delay time accuracy.

    -Michael

  • Dear Michael,

    Thank you very much for your quick response.
    I understand.

    Best regards,
    Seishin