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TPS3828-33 watchdog IC

ikon
Genius 5355 points

Hi Support,

What is the maximum pull down value allowed on the WDI pin (pin 4) to keep the watchdog enabled?

Thanks.

  • 0
    TI__Expert 6825 points
    Hi Ikon,

    In the functional block diagram it shows that there is a 40k resistor coming from the internal oscillator. If you want the watchdog to still be enabled then the effective resistor divider created by this and the pull-down resistor will have to create a logic low, which is why the maximum recommended pull-down resistor is 1k.

    Best Regards,
    Mark
  • 0 in reply to Mark Sellers
    Genius 5355 points

    Hi Mark,

    I saw this 1kOhm resistor in the design note, but it did not state that it is the maximum value.

    So I would like to know based on what I can decide the pull down value. We tried to use 10kOhm resistor and it works.

    So it must be a parameter such as port output current together with the Vil (input voltage low threshold) specification to define the pull down resistor.

    Thanks.

  • 0 in reply to ikon
    TI__Expert 6825 points
    Hi Ikon,

    You are correct it will depend on the Vil threshold and the input current to the pin. The lower threshold voltage is .3*Vdd so if the resistor divider between the 40k resistor and the pull-down resistor keeps the voltage below this point it should work. However, the part was designed, characterized, and tested with a 1k resistor, so increasing this resistance should be thoroughly validated.

    Best Regards,
    Mark