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TPS3808 and LM8365 maximum delay

David Dean
Expert 2305 points
Other Parts Discussed in Thread: TPS3808, LM8365

Hello,

  The TPS3808 datasheet mentions an adjustable delay from 1.25ms to 10s.  Is there any reason why I can't use a larger capacitor to get even more delay?  I am hoping for a 20 second delay, which would require a 3.5uF capacitor (or a nearby standard value).

Thanks,

Dave

  • 0
    TI__Mastermind 40435 points

    Hi David,

    Having a larger Ct cap will create a larger discharge current which may damage the device. In addition, the having larger cap may not discharge the capacitor fully and the actual delay time may vary.

    It is possible to cascade 2 devices set to 10s so that you get a total of 20s.

    Regards,

    Darwin

  • 0 in reply to Darwin Fernandez
    Expert 2305 points

    Hi Darwin,

      LM8365 is a similar part except the delay is handled a bit differently.  Does this part also have a maximum allowable capacitance, and if so, what is it?

    Thanks,

    Dave

  • 0 in reply to David Dean
    TI__Mastermind 40435 points

    Hi Dave,

    Unfortunately it is not specified in the LM8365 datasheet, so you may or may not have the same problem when increasing the Cd capacitance. I recommend requesting samples of this device and measuring its performance on your applicaiton.

    Typically, the time delay is used to ensure some time for the output voltage to settle before enabling another IC or releasing a RESET on a microprocessor (usually it takes on the order of a couple ms).

    Regards,

    Darwin

  • 0 in reply to Darwin Fernandez
    Expert 2305 points

    Darwin,

      I have a board with the LM8365 on the way.  If I add a large capacitor and I get the long delay that I want, am I good to go?  You had mentioned a risk of too much capacitance damaging the part - even if I get the correct delay, could I end up with a problem down the road?  Is there anything I can measure to see if I could damage the part?  Capacitor discharge current, something like that?

    Thanks,

    Dave