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Original question:

CC3235MODASF: Power-up reset not working

CC3235MODASF: Module not starting up properly - Follow-up to problems I reported reported March 2023

Chris Miller79
Intellectual 460 points
Part Number: CC3235MODASF

Quick summary of issue:  I had two near-identical designs of PCB using the CC3235MODASF.  The more recent one was giving severe problems starting up correctly on powerup.

Please refer to earlier thread https://e2e.ti.com/support/wireless-connectivity/wi-fi-group/wifi/f/wi-fi-forum/1202094/cc3235modasf-power-up-reset-not-working for massive levels of detail on work carried out.

That thread is now locked, so I can't post the solution with it (if a moderator is able to tack the following text to the end of that case, it would be tidier...)

Now, revisiting the problem, I have at least found a solution, even if I don't really understand it.

I discovered that the device would power up correctly if I had 'scope probes connected to the programming connector Tx and Rx pins.  These would provide a slight DC leakage to path (about 10Meg).

I found that adding two 4.7Meg resistors to ground from pins 46 and 47 mean that the SoM now starts up properly.

It is quite bizarre that two PCB layouts, almost identical, in terms of tracking of those two lines behave so differently, but it is absolutely repeatable.

  • 0
    TI__Mastermind 46125 points

    Hey Chris,

    That is strange, but that's the life of a HW engineer. I'm glad you were able to get a repeatable solution.

    Before adding the 4.7M ohm pulldowns, were there any other pulls on those lines?

  • 0 in reply to Dylan Hubbard
    Intellectual 460 points

    Thank you for your response.

    The lines were completely open circuit, which I guess is always a bad idea.  I can't see any obvious way to configure pullup/pulldown on lines used for a UART Tx & RX  in Code Composer>Syscfg.  (in any case, I don't think any pulls configured that way would take effect until the application code is called - and we weren't getting that far.)