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AM3358: Power sequencing question

Brian Weir
Intellectual 810 points
Part Number: AM3358
Other Parts Discussed in Thread: TPS65217

 BBB reference custom AM335x board design using a PMIC TPS65217C.

I have not scoped the power sequencing outputs of the TPS65217.  There are times when the processor will not start (all voltages are present) and I was curious if it were power related. 

If this is an issue, how is it tested, verified, and corrected?

Regards,

Brian Weir

  • 0
    TI__Guru**** 393215 points
    TPS65217x PMIC are designed to work with AM335x devices and their power-up sequencing has been verified.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 810 points
    Biser, Thank you for the reply.

    I understand in a perfect world the intent of PMIC power sequencing is to correctly start a AM335x, this sequencing was most likely tweaked, centered, and agreed upon by several competent Engineers prior to being verified. However, what if the AM335x does not start every time the PMIC has 5v power applied?

    The question is: If the AM335x power sequencing were incorrect possibly due to a defective (or slowly dying) PMIC chip would this prevent the processor from starting? Is the sequencing of one rail over others critical, are there timings that I should verify?

    Regards,
    Brian
  • 0 in reply to Brian Weir
    TI__Guru**** 393215 points
    No, I don't believe that PMIC timings are causing the issue you see. What comes to mind is that you should check your main oscillator and SYSBOOT values at reset release time. Here is a wiki with some tips: processors.wiki.ti.com/.../AM335x_board_bringup_tips
  • 0 in reply to Biser Gatchev-XID
    Intellectual 810 points
    Thanks Biser, referring to the link you suggested... I wonder if the processor not starting could be related to the AM335x not receiving the PORZ signal PGOOD properly from the TPS65217 PMIC? Unfortunately I never looked at PGOOD. Soon after having these intermittent processor startup problems, the PMIC chip failed and it's SYS output was at .8v with no output on the regulated rails. I'm having the PMIC chip replaced and xrayed.

    Regards,
    Brian
  • 0 in reply to Brian Weir
    TI__Guru**** 393215 points
    It's highly unusual that this PMIC should fail. Have you carefully checked your schematic/layout for possible errors? One thing that comes to mind - check that the PMIC center pad is properly soldered. I've seen issues in the past, where the PCB manufacturer had covered the center pad with solder mask.