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AM335x BeagleBone Black PMIC/boot issue

BillyO
Genius 17555 points
Other Parts Discussed in Thread: TPS65217

Hi team,

The Sitara team had asked me to post this here:

My customer is using a BBB that is running wec7 and PMIC TPS65217C. They are up against some powering/booting issues and would like some feedback about what this could be. Here is the high level:

Trying to use the battery charger, however when the battery is connected they were unable to turn the board off by holding the button populated at the board.

-What is the register configuration for disable the board to save power?

-Could you tell us the sequence in order to do that?

From the spec, it looks like that the battery voltage is always on at sys pin.

-The other problem area is:  when the battery status is not ok, like undervoltage status , the BBB does not boot up even when its at an ac adapter.   How could they avoid that ?

Thanks in advance for the help,

Billy

  • 0
    TI__Genius 10885 points

    Hi Billy,


    You are correct that the battery voltage will appear on the SYS pin even while OFF, so holding the button down will not turn off the SYS_5V on the BBB when operating with a battery.

    Turning the PMIC OFF requires setting the OFF bit to 1 in the STATUS register, and is then permitted by dropping the PWR_EN pin voltage on the PMIC, which is controlled by the PMIC_POWER_EN pin on the AM335x. This can be referenced in section 9.4.1 of the TPS65217 datasheet. Doing so will turn off the core and power rails to the AM335x, but since the battery is still present there will still be a voltage on the SYS_5V rail.


    A rising edge on the AC adapter after their UVLO event should start the PMIC, same as with a rising edge on the USB. Additionally, they should be able to press the push-button to create a new start condition if the AC is already supplied, and in the worst case they can reset the PMIC.


    Do you know how they are getting to this UVLO condition when the AC power rail is present?

  • 0 in reply to Richard Solarski
    TI__Genius 17555 points

    Thanks for the help on this Richard.

     

    The customer took a little time but is back with their answer/elaboration:

     

    At BBB vsys is always attached to Sitara [see below] . When we hold the button the system turns off ( if the battery is not available) , it means that the  system  is executing pmic poweroff routine, but when the battery is available the board goes down also, but after a short time it is powered on again .  It looks like that the same routine is being executed and the only difference is the battery .  How could we avoid that ?  Could you suggest any external circuit ?

     

    Thanks,

    Billy

  • 0 in reply to BillyO
    TI__Genius 10885 points

    Hi Billy,

    I believe the biggest indicator here is how VLDO1 is operating, since it will ultimately supply the PWR_EN pin which controls the OFF state. If you look at Figure 20 in the TPS65217 datasheet, you'll see that the push-button does not actually lead to an OFF state (top right), but instead has a branch that resets and returns to WAIT PWR_EN.

    When operating off the battery on our EVM, VLDO1 would recover after the 1s fault delay, whereas AC would not always have this behavior. This is attributed to the VSYS supplying VINLDO, as AC cannot supply VSYS in off or reset state, whereas BAT can, letting VLDO1 regulate, and reasserting the PMIC's PWR_EN.


    Could they monitor VLDO1 (or PWR_EN) and confirm if this is their situation?