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Delay for TPS3808

Atsushi Yamauchi
Genius 4810 points
Other Parts Discussed in Thread: TPS3808, TPS3890

I would like to confirm delay of TPS3808.

1. For Figure 3, what is "RESET Timeout"?   

    Does it equal "tD"?

2. Do you have the variation data for tD (CT: none and 3300pF)?

Best regard,

Atsushi Yamauchi

  • 0
    TI__Mastermind 43630 points

    Hi Yamauchi-san,

    1. Figure 3 shows graphically how to program the delay. it Shows up to 10s delay because the Ct charging current is only 220nA. So the limitation is really a function of the leakage of the capacitor used on the Ct pin. The concern can be a PCB with contamination may have too much leakage and the timer may never expire if too large of a capacitor is chosen. For this reason we strongly recommend using X7R dielectric capacitors. Also, we have just released the improved version which is the TPS3890. This has the ability to program the delay up to 30s and has a much stronger Ct pin charging current.

    2. If Ct is pulled up to VDD with a resistor the timing is fixed to 300ms, if left floating it is a fixed 20ms delay. By adding a capacitor you can program the delay as required by the application.

    I hope this helps.

    Regards,

  • 0 in reply to JCHK
    Genius 4810 points

    Dear John-san,

    Thank you for your reply.

    I understood No.1.

    I have questions for No.2.

    a. When Ct pin left floating, the delay is 20 ms.

        And when Ct is 3300 pF, it is about 20 ms too. Which do you recommend for 20 ms delay (which is the variation of delay small)?

    b. Could you please variability data of the delay for Ct floating and 3300pF or other value of Ct ?

    Best regards,

    Atsushi Yamauchi

  • 0 in reply to Atsushi Yamauchi
    TI__Mastermind 43630 points

    HI Yamauchi-san,

    I am not sure if we have statistical data comparing 3300pF vs. simply leaving the Ct pin floating. However, over temperature there should be some variation in our current source that is charging the Ct capacitor. So I would have to believe that leaving it floating is far more accurate. My reason is because with a 3000pF capacitor, you have to account for the variation over capacitors(Actual capacitance and leakage) vs. temperature. I believe that the the combined variation in our sourcing current and Ct capacitance should have a much wider tolerance than simply leaving it floating.

    Regards,

  • 0 in reply to JCHK
    Genius 4810 points

    Dear John-san,

    Thank you for you reply.

    I understood floating is better than 3300pF capacitor for 20ms.

    If possible, could you provide the distribution data of the delay by floating (some piecies, some lots and so on)?

    Best regards,

    Atsushi Yamauchi

  • 0 in reply to Atsushi Yamauchi
    Genius 4810 points
    Dear John-san,

    How about is the previous request?
    Could you please reply it?

    Best regards,
    Atsushi Yamauchi
  • 0 in reply to Atsushi Yamauchi
    TI__Guru 55940 points

    Hi Yamauchi-san,

    Sorry for the delay.  For 1906 units the mean delay is 19.728 with a standard deviation of 0.35.

    Very Respectfully,

    Ryan