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BQ40Z50-R1: PCHGC recovery threshold: should it be positive or negative?

Martin Unsal
Prodigy 130 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQ40Z50

In BQ40Z50-R1 Technical Reference, section 2.20, OverPreChargingCurrent() Protection: "This protection is designed to recover by a discharge event; therefore, PCHGC:Recovery should be set to a negative value in data flash."

However in 14.9.24.3, the default value is 10 mA (positive). Which is correct?

I'm not sure if this protection can work reliably with either a positive or a negative value of PCHGC:Recovery. If the value is positive, then the PCHGC protection will toggle on and off continuously as long as an overcurrent is applied, with a period of (PCHGC:Delay + PCHGC:RecoveryDelay).

On the other hand, if PCHGC:Recovery is negative, then you need to discharge in order to reset the protection. However the CUV protection will prevent discharging in some of the precharge voltage range. So in that case PGHGC protection becomes unrecoverable.

Any advice? Am I missing something?

Thanks

Martin

  • 0
    TI__Mastermind 25955 points
    Hi Martin,

    The bq40z50-r1 device expert will update this thread by COB on Tuesday. Thank you!

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    TI__Mastermind 25955 points
    Hi Martin,

    Please let me know if the device expert has not reached out to you via other means.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 130 points

    Hi Bryan,

    I haven't heard anything on this.

    Thanks,
    Martin

  • 0 in reply to Martin Unsal
    TI__Genius 10830 points
    hi Martin,
    This post has been assigned to another BMS engineer.

    Regards,
    David
  • 0
    TI__Mastermind 34775 points
    Hi Martin,

    I'm not the expert referred to in the post, but I can help. It's poorly written in the TRM. All values are positive including the PCHGC:Recovery threshold e.g. 10mA. What is meant for recovery the current must fall below the PCHGC Current threshold by the set PCHGC:Recovery threshold for PCHGC:RecoveryDelay for the protection to clear.

    Example: PCHGC Current threshold = 50mA and PCHGC:Recovery threshold = 10mA then the charge current must fall to below 40mA for the PCHGC to clear.

    Hope this helped.
  • 0 in reply to Damian Lewis
    TI__Intellectual 1365 points

     As Damian mentioned, it is recovered when the Current() is < PCHGC:Recovery Threshold. If you want to recover it at discharging condition,it should be set to a negative value.

     As you mentioned, if it is Min Cell voltage < CUV : Threshold, DSG FET is off but CHG FET is on. So,it exits CUV condition during pre-charging.

    When Min cell voltage < CUV and Current() > chargingcurrent() + PCHGC:Threshold for delay because the charger IC is not working properly, both CHG() and DSG() will be off as corner case. In this case, I'd recommend to set PHCGC : Recovery Threshold > 0 since CHGFET will be recovered if you unplug the charger.

  • 0 in reply to Jasper Yi
    Prodigy 130 points

    Hi Damian and Jasper,

    Thank you for your responses. My concern with positive PCHGC:Threshold is that the protection will toggle on and off continuously in the case of a defective charger or other abuse. Here is the observed sequence of events:

    1. Charger applies excess current to battery in precharge
    2. After PCHGC:Delay,PCHGC protection trips
    3. Due to PCHG FET being disabled by PCHGC protection, charge current will go to 0
    4. After PCHGC:RecoveryDelay, PCHGC protection will clear, enabling PCHGC again
    5. Goto 1

    Thus the BQ40Z50 does not protect against excess precharge current. The cells still see the full excess current throughout precharge interval, just intermittently, with duty cycle equal to (PCHGC:Delay / (PCHGC:Delay + PCHGC:RecoveryDelay)).

    Does TI have a recommendation to avoid this?

    Thanks

    Martin

  • 0 in reply to Martin Unsal
    TI__Intellectual 1365 points
    Hi Martin,

    If PCHGC >0, then it could not be avoided. So, we recommended to set the PCHG: Recovery Threshold to Negative value. However, it is not recovered if Min cell voltage < CUV:Recovery threshold and your charger is defective as you mentioned. I think you have to determine whether you want to keep charging when your charger is defective or not.
    Charge current will be on and off even though you set the PCHG:Recovery Threshold to negative value if your defective charger IC is in supplement mode and Min Cell voltage is normal status.
  • 0 in reply to Jasper Yi
    Prodigy 130 points
    OK I understand, thanks!