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BQ40Z50-R2: Will not charge unless there is SMBus communication with the part.

Joe Perino
Intellectual 640 points
Part Number: BQ40Z50-R2

Hello,

I presume the problem we are observing is related to a flash setting, however, we are at a loss to identify which one.

Our battery pack design functions just fine; except the battery will not charge at all unless there is SMBus communication with the part.  As soon as the SMBus is disconnected, or communication stops, charging stops.

NR=1 and the charge FET is configured to be ON in sleep mode.

Thanks,

Joe Perino

  • 0
    TI__Mastermind 42535 points
    Joe,

    There is no setting that mandates comms with the gauge for charging. Can you please send me your srec/gg.csv? I'll look into it for you.
  • 0 in reply to Batt
    Intellectual 640 points

    Hello Batt,

    Thanks.  I actually was not implying there was a specific setting, but rather suspected a setting that was causing the part to go to sleep or shut down or into some other mode where the CHG FET would turn off.

    If the SMBus is not active, charging will not start.

    If the pack is charging, when the SMBus communications stop, charging stops about 5 seconds later.

    I have attached the .srec and .gg files.

    If that doesn't work I can email them.  I have had trouble uploading files in the past.Thanks,

    Joe Perino

    SN_20180716_MH1_golden.gg - Copy.zip

  • 0 in reply to Joe Perino
    Intellectual 640 points
    Hello,

    The datasheet indicates that if the PTC/PTCEN is to be disabled they should be connected to Vss. I reviewed the layout for this board, and PTCEN is connected to ground, but If PTC is left floating could/would that be a potential cause of the problem with the charge FET? We see no issue on discharge at all. Only charge.

    Thanks,
    Joe P.
  • 0 in reply to Joe Perino
    TI__Mastermind 42535 points

    No, PTC can't be a cause of this though if you have a weak connection on the PTCEN it will immediately disable chg. You can leave PTC floating if PTCEN is connected to GND. The only issue I see in the gg is that you need to change Power-Power-valid update voltage to 3500mV from 10000mV. Setting NR=1 requires the smbus lines to be high. Try resetting NR and see if your charging stops.

  • 0 in reply to Batt
    Intellectual 640 points
    I went through the fault enable/fault disable registers one bit at a time to see if a fault condition was disabling the Charge FET.
    The only fault that had any effect is the Host Watchdog Timeout. This setting would actually make sense, since it is monitoring the SMBus for valid communication. The timeout is set for 10s, which is about how long it takes charging to stop if SMBus communication stops. If I change the timer setting, charge termination without SMBus follows the setting of the register.

    Here is the problem. When I disable the HWDF fault in the Enabled Protections C register by setting HWDF=0, the pack will not charge at all. If the fault was disabled it should solve the problem.

    None of the other faults have any effect whatsoever on charging being terminated after 9-10 seconds, so this has to be the issue. The only problem is that I cannot disable the fault because when HWDF=0 the pack will not charge at all. SS=1, XCHG=1, and the CHG FET turns off.

    The issue seems to be a bug in the firmware of the bq40z50R2. We have packs waiting for DOT and UL certification testing that cannot be cycled so we really need this issue resolved asap.

    Thanks,
    Joe Perino
    VP&GM
    Nova Battery Systems
  • 0 in reply to Joe Perino
    TI__Mastermind 42535 points
    Joe,

    Thanks for digginf further into this. You are right. I didn't see the HWDF being set. That can cause issues. This is why it's default is set to 0. Did you send a reset after disabling the HWDF protection? You need to make sure that is done for the setting to be loaded into memory. I just tested HWDF here and am seeing the chg fet stay on despite having no comms and the smbus lines floating.

    The possibility here is that since your Valid Update Voltage was set to 10V, if your pack went below 10V, you wouldn't have been able to write to DF and therefore would not have been able to reset HWDF. Please try with a fully charged pack and set your Valid Update Voltage to 3500mV and write to df. That should fix it. This isn't a bug.
  • 0 in reply to Batt
    Intellectual 640 points
    The pack is 4s so the pack voltage is 15V nominal. I still lowered the Update Voltage setting, but without doing that sending a reset worked. After the reset, the pack charges fine without the SMBus. Thank you for your time and effort.
  • 0 in reply to Joe Perino
    TI__Mastermind 42535 points
    Thank you for using our gauge. I appreciate your kind words.