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BQ25121A: "Brick Mode"

Keith Creedy
Prodigy 20 points
Part Number: BQ25121A
Other Parts Discussed in Thread: BQ25120, BQ25120A

Hello,

We have a wrist-worn device in the final phases of development, but our BQ25121A is experiencing a severe issue holding us back from going to market.  The device enters, what our testers call, "Brick Mode" under the following conditions:

1. If the BQ25121A enters ship mode.

2. If the battery discharges to VBAT < BUVLO.

To exit "Brick Mode," holding down MR or toggling it doesn't work, plugging the device in doesn't work either.  The only way to exit "Brick Mode" is by detaching and reattaching the battery.

Observations while bricked:

VBAT = 4.0v

PMID = 4.0v

SW = 0v

LDO = off

Since both Ship Mode and battery discharge below BUVLO disconnects the battery with an internal FET, we believe that's where the problem lies.  When in Ship Mode, the device should disconnect the battery thus PMID should also be 0v.  We believe that the device is failing at this point, crashes, and doesn't respond or wake-up to MR or VIN.

This "Brick Mode" state has been on this forum before, although with the BQ25120 and BQ25120A.  The forum links are below, I do not see this issue being resolved so we cannot fix based on those forum posts.

https://e2e.ti.com/support/power-management/f/power-management-forum/786547/bq25120-bq25120-problem-with-capacity-on-mr-line?tisearch=e2e-sitesearch&keymatch=BQ25120a%25252520SW

https://e2e.ti.com/support/power-management/f/power-management-forum/954416/bq25120a-can-t-exit-ship-mode-from-vin-insertion?tisearch=e2e-sitesearch&keymatch=BQ25120a%20brick%20mode

Thank you, in advance, for your assistance.

Keith Creedy

  • 0
    Prodigy 20 points

    EDIT:

    When we try to put the device into ship mode:

    VBAT = 4.0v

    PMID = 4.0v

    SW = ~350mV

    LDO = ~150mV

    When VBAT < BUVLO

    VBAT = 3.0v (does not charge, even after hours plugged in)

    PMID = 0.9v

    SW = ~350mV

    LDO = ~150mV

  • 0 in reply to Keith Creedy
    TI__Mastermind 19195 points

    Hi Keith,

    We are looking into this you can expect a response by end of the week. 

    Thanks,

    Nick

  • 0
    TI__Genius 12475 points

    Hi Keith,

    I would like to see schematics around this device and any waveforms of VIN/ VBAT/ MR/ SYS/ PMID. When is the shipmode command given? 

    I can reach out to you over email. 

    Regards,

    Gautham

  • 0 in reply to Gautham
    Prodigy 20 points

    Hi Gautham,

    Attached is a schematic and the PCB traces.  We used traces between the pads, do you think that has something to do with this issue?

    Additionally, I notice that when it is bricked from VBAT < BUVLO and it is not plugged in, PMID is 0.43V.  And when I plug it in to 5v supply, PMID is 1.36v.

    I do not have access to waveforms.

  • 0 in reply to Keith Creedy
    TI__Genius 12475 points

    Hi Keith,

    Thanks for sharing the schematic and layout file. Traces in between the pad is okay as long as the PCB manufacturer is able to build them. 

    One thing I quickly noticed was the IPRETERM/ ISET and ILIM pins are floating which might be an issue. GND them is okay as the device will just use the internal register values but leaving it floating needs to be checked. 

    Also do you have the portion of the schematic for the /MR- labelled SW3 on the schematic?

    I will get back to you. 

    Regards,

    Gautham

  • 0 in reply to Gautham
    Prodigy 20 points

    Hi Gautham,

    Thanks for the quick reply.

    Good to know about those floating pins.  On the previous PCB, we had resistors connected to those and experienced the same "Brick Mode" when we tried to enter Ship Mode.

    Here is an image of the button we have connected to MR / SW3.

  • 0 in reply to Gautham
    Prodigy 20 points

    Also, we worked with our manufacturer, PCBWay, to define the width and spacing of the traces.  They were confident that it is ok.  We have four PCBs in this configuration and all four experience this problem.