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Can I use a 68nF cap on the TPS3813K33 even though datasheet says 63nF？

Jacky Chen29
Genius 4735 points
Other Parts Discussed in Thread: TPS3813, UCC3946

Hola,

Just want to confirm with you that are there any side effect or impact if I'm using 68nF capacitor as for 20s delay time application？

Can you also recommend the watchdog IC which can make the Twindow at least 20s for WDI, and the WDO reset timing delay at least 200ms. Thanks ～

  • 0
    TI__Guru 50190 points

    Hi Jackie,

    The Datasheet recommends a maximum value of 63nF. While this likely has quite a bit of margin, the key concern is making sure that the WDT pin sees a capacitor instead of being connected to GND:

    So a larger cap may be seen as being connected to GND vs. what you are looking for in the below:

    Regards,

  • 0 in reply to JCHK
    Genius 4735 points

    Hola John,

    Thanks, but I still have a question about the tolerance of the window frame, why 25% tolerance for max & min which shown in datasheet page9.

    max=1.25*twindow、min0.75*twindow. Is it means the external capacitor or TPS3813 internal tolerance？

    Meanwhile, can you tell me directly that can I use 68nF capacitor as our application for min 20s long delay time？

    Thank you so much

  • 0 in reply to Jacky Chen29
    TI__Expert 3910 points

    Hi Jackie,

    The ±25% variation of the part itself, and it does not take into account the variation in the capacitor you might use, also, we do not recommend going outside of the specified CWP value range (i.e. 155 pF ≤ CWP ≤ 63 nF).

    Perhaps you could consider using UCC3946, which has been recommended for longer delays.

    Best Regards,
    Victor