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TPS3828: High impedance of WDI

David Kim2
Genius 3305 points
Part Number: TPS3828

Tool/software:

Hi

RESET phenomenon occurred when testing WDI pins in floating state.
Referring to the relevant E2E, we solved it by adding the 10 Mohm resistance induced by the high impedance.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1013038/tps3828-q1-about-way-of-disable-of-watchdog-timer-wdi?tisearch=e2e-sitesearch&keymatch=tps3828%2525252520wdi#


I have solved it, but I would like to ask you about the reason.

1. Isn't floating high impedance?
2. No reset after applying high impedance 10 Mohm, what's the difference from floating status?
3. Is there a reason why you induced 10M resistance with high impedance?

Thanks

  • 0
    TI__Mastermind 18071 points

    We apologize for extended delay due to year-end holidays. Your post will be answered in the next 10-12 days.

  • 0 in reply to Masoud Beheshti61
    TI__Mastermind 18980 points

    Hi David,

    For the TPS3828, when disabling the watchdog, the input impedance, Rin, behaves as a voltage divider with the 40K, and as long as the resulting HIGH pulse on the transition detection node is greater than the Vih, the watchdog will stay disabled. An Rin of 100K and above should do the trick for this device. Something to note though, the 100k value will put you on the border of the Vih, while the 10M will give your the .9999*VDD on the transition detector. 

    Now for your question, Yes, typically floating and high impedance are synonymous. For your chase, did you happen to measure the impedance between WDI and GND when the pin is set to floating? 

    Jesse