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BQ76942: Sleep mode consumes 83uA not 24-41uA.

Fabian Wärn
Prodigy 10 points
Part Number: BQ76942
Other Parts Discussed in Thread: EV2400, , BQSTUDIO

Tool/software:

Hi I have a battery issue where new batteries produced consume 83uA in supposed sleep mode. When i connect the to the BQ76942 using the EV2400 i can read SLEEP is enabled. When I unseal and full-unseal the device to read the settings the battery will change current consumption to the intended 24uA. All batteries unsealed will change to draw LESS current when unsealed than sealed. Why is this? Is there a configuration which only affects the sealed mode?

When in unsealed mode the battery will flicker between 24uA and ~110uA for about 1-2min before stabilising at 24uA. Is the 83uA read some sort of average value read in sleep mode? Why won't it stabilise in sealed mode then?

Kind regards Fabian

  • 0
    TI__Expert 4320 points

    Hello Fabian,

    You are right, this current value is an average over time. During SLEEP MODE the device will wake up and take measurements. This time window by default is every 5 seconds:

    The DMM integration time needs to be long enough to capture the whole window. Otherwise, current measurements may not be accurate over time.

    Can you send a screenshot of your bqstudio dashboard with status registers showing?

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Prodigy 10 points

    Sleep voltage time is set to 41sec to minimise the current consumption. If the 83uA is average consumption why would it in unsealed mode consume less (24uA) than in sealed mode (83uA)?

  • 0 in reply to Fabian Wärn
    TI__Expert 4320 points

    Hello Fabian,

    Is this reproducible? 

    The sealed, unsealed, and full-unsealed should not have an effect on current consumption.

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Prodigy 10 points

    After unseal I cannot reproduce the issue on the batteries the have to come from our production. The following happens after unseal.

    1. The current flickers bewteen 24uA and 110uA for about 1 min when in sleep mode. Then it stays at 24uA. (Before unseal it was just consuming 83uA).

    2. When I use the EV2400 to set the sleep mode it does not flicker and goes directly to stable 24uA.

    3. After re-sealing the same behaviour as 1. is observed.

  • 0 in reply to Fabian Wärn
    TI__Expert 4320 points

    Hello Fabian,

    Can you send a waveform of the current draw measured at the BAT resistor when you go from sealed to unsealed?

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Prodigy 10 points

    Hi!

    Here are the measurements. First picture is when sending seal command with EV2400 and the second is when sending unseal.

    Seal

    Unseal

    I am wondering what you are trying to find out with this information? Perhaps I can supply you with more info if I understood.

    // Fabian

  • 0 in reply to Fabian Wärn
    TI__Expert 4320 points

    Hi Fabian,

    I was trying to see if the current would when entering and exiting sealed mode.

    I will see if I can recreate on bench and give you feedback by tomorrow.

    Can you send the schematic and the .gg file?

    Best regards,

    Thomas Rainey

  • 0 in reply to Fabian Wärn
    TI__Expert 4320 points

    Hi Fabian,

    I could not recreate the behavior your are seeing on a test bench. I saw no difference in current draw between sealed and unsealed mode.

    If you send your schematic and .gg file I can look over those.

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Prodigy 10 points

    Hi Thomas after testing entering and exiting sealed and unsealed mode I continued to test and check current consumption in CFG_MODE. This was the only mode where current consumption was not specified in the data sheet. It would seem like I am not exiting the CFG_MODE even though the module is in sealed mode. We are now looking in to if the exit CFG_MODE step is unsuccessful in production. If the these tests are successful I will resolve this issue otherwise continue discussion.

  • 0 in reply to Fabian Wärn
    TI__Expert 4320 points

    Hi Fabian,

    Sounds good, keep me updated.

    Best regards,

    Thomas Rainey