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BQ40Z50: Shifting from 2P3S BQ20Z655 to 3S BQ40Z50-R5 is not straightforward.

Yishai Abramov
Prodigy 35 points
Part Number: BQ40Z50

Hi to all,

Recently, we have shifted our Battery pack balancing IC to BQ40Z50-R5 from BQ20Z655. Unfortunately, it is not as straightforward as expected.

The battery pack is a 2P3S pack cell arrangement, which is the new battery pack based on the BQ40Z50-R5 balancing IC.

We have some unclear behavior related to SMBus DAT/CLK pins, and we can't understand it; as the SMBbus lines are connected to the host, the battery pack reset after ~3 seconds.

When one of the SMBus lines is disconnected, the battery does not reset, and the system boots up. I'm attaching the Battery connection scheme and the BQ40Z50-R5 log and configuration table.

Please, Any suggestions would be welcome, and any assistance would be appreciated.

Thanks,

Yishai,

BQ40Z50-R5 cfg.csv0728.log.log

  • 0
    TI__Mastermind 37761 points

    Hello,

    I will look into this. I will get back to you by tomorrow.

    Regards,

    Nick Richards

  • 0 in reply to Adrian
    Prodigy 35 points

    Hi Nick,
    I appreciate it,
    Thank you,
    Yishai,

  • 0 in reply to Yishai Abramov
    TI__Mastermind 37761 points

    Hello Yishai,

    SMBus regulations are not the same in both devices. You must follow BQ40z50 SMBus specs. The pull ups requirement are different. Please review the datasheet for the BQ40z50

    Regards,

    Nick Richards

  • 0 in reply to Adrian
    Prodigy 35 points

    Hi Nick,

    Thank you for your reply,
    I can't find any mentions for SMBus pull-up RES; please refer me.


    At this opportunity, I would like to share one more strange behavior.
    During our attempt to turn off all the sleep registers (DA Config), we also accidentally cleared the CC1 (CELL cfg) bit. BQ40Z50 now monitors only one cell (1S2P cfg).
    Without noticing this, we assembled the battery with the change, and the system booted up successfully. To our astonishment, we were sure that the SLEEP bit was the issue until we noted that the battery pack showing 4.2V with a total state of charge.

    We made one more step and took the following tests:
    1. Configured back to 3S2P cfg. The system resets after ~3 seconds.
    2. Configured battery, 2S2P cfg. The system resets after ~20 seconds.
    3. Configured battery, 1S2P cfg. The system does not reset.
    4. The tests above have the same pull-ups for SMBus lines and the SMBus line connected to the host.

    Please advise,

    Thanks in advance,

    Yishai,

  • 0 in reply to Yishai Abramov
    Prodigy 35 points

    Sorry,

    I made a mistake. Please see the correct information below for the following steps, the battery reset.

    We made one more step and took the following tests:


    1. Configured back to 3S2P cfg. The battery resets after ~3 seconds.
    2. Configured battery, 2S2P cfg. The battery resets after ~20 seconds.
    3. Configured battery, 1S2P cfg. The battery does not reset.
    4. The tests above have the same pull-ups for SMBus lines and the SMBus line connected to the host.

    Yishai,

  • 0 in reply to Yishai Abramov
    TI__Mastermind 37761 points

    Hello,

    Today's a holiday and no one is in the office. We will get back to you tomorrow.

    Regards,

    Nick Richards

  • 0 in reply to Yishai Abramov
    TI__Mastermind 37761 points

    Hello Yishai,

    We usually recommend 10K pull up resistors for the SMBus communication lines. You can review the specs sheet for SMBus.

    When you say "configured", do you mean that the battery pack is setup in those configuration as well as setting the correct CC bits.

    Regards,

    Nick Richards

  • 0 in reply to Adrian
    Prodigy 35 points

    Hi Nick,

    I already changed the pull-up resistors to 10k, but still, without any success, I got the same results.

    In the configuration, I meant I was changing the registers of the BQ40Z50 through the studio. See the picture below for cc0 cc1 bits of the DA Configuration register.

    Thanks,

    Yishai,

  • 0 in reply to Yishai Abramov
    TI__Mastermind 37761 points

    Hey Yishai,

    Yes, for CC bits, that should be configured properly for the number of cells in series you have for your application. Having any other configuration that's not appropriate for your battery will cause issues.

    Regards,

    Nick Richards