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Error switching from TPS65910A3 to TPS65910A31

Sam Parkinson
Prodigy 85 points
Other Parts Discussed in Thread: AM3354

Hi,

We currently have a working product which uses the TPS65910A3 PMIC to power a AM3354 processor.

We currently do not use the PMIC's VRTC 1.8V rail, the RTC domain of the AM3354 is powered by a dedicated regulator.

The PMIC's VRTC rail is only connected back to the BOOT1 IO pin.

Recently we manufactured a number of PCB's with the TPS65910A31 part.

None of these boards will boot. In each case the VRTC rail is active but no other rails come up.

Asserting the PWRHOLD line to 1.8V or dropping the PWR_ON line from 5V to 0V seems to have no response.

I have reworked one of these boards to put the A3 part back on and the rails power up as expected, it seems that either.

  1. The A31 parts are faulty.
  2. The design is valid for the A3 part but not the A31?

Questions:

  1. Is there anything you can suggest that I try in order to get these boards to boot using the A31 chip?
  2. Is there any requirement to actually load the VRTC rail in the A31 part?
  3. It almost seems like the internal RC oscillator is not running, is there any way to verify this?
  4. Is there a strict requirement to ground the OSC32KIN pin when running from the internal oscillator, I assume not if the chip allows for switching to external after boot?
  5. Can you think of any reason why a design which works with the A3 part would not be compatible with the A31?
  6. If we take a A3 chip and change the VRTC_REG.VRTC_OFFMASK bit to 1 is this effectively the same as an A31 chip?

  • 0
    TI__Genius 17380 points

    Hi Sam,

    1. Is there anything you can suggest that I try in order to get these boards to boot using the A31 chip? [K] Have you tried reworking a board and adding a new A31 chip? Perhaps the manufacturer was not successful in installing the part.
    2. Is there any requirement to actually load the VRTC rail in the A31 part? [K] No
    3. It almost seems like the internal RC oscillator is not running, is there any way to verify this? [K] CLK32KOUT would only be released after power sequence has mostly completed.
    4. Is there a strict requirement to ground the OSC32KIN pin when running from the internal oscillator, I assume not if the chip allows for switching to external after boot? [K] I will look into this. 
    5. Can you think of any reason why a design which works with the A3 part would not be compatible with the A31? [K] No, I could see that an A31 design wouldn't work with an A3, but an A3 design should work with an A31. 
    6. If we take a A3 chip and change the VRTC_REG.VRTC_OFFMASK bit to 1 is this effectively the same as an A31 chip? [K] Yes

    One additional thing to check is that BOOT0 = 0, and BOOT1 = 1. If not, then the part number is ignored and default EEPROM is used.

  • 0 in reply to Kevin LaRosa
    Prodigy 85 points

    Thanks Kevin,

    A couple of updates on the issue

    1. We have since replaced one of the A31 chips with another from stores and the issue remains the same
    2. We have replaced another A31 chip with an A3 and the board boots correctly.

    As it stands it is likely that we have some faulty stock of parts. I will contact our local supplier and see if the parts can be returned to TI for test / replacement.