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BQ40Z50-R1: Simultaneous OCD and TC/TCA Condition

Andrew Elgar
Prodigy 110 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQ40Z50

Hello,

For our application, we are making a battery pack with an integrated charger using the bq40z50-R1 and a charger IC communicating over SMBus. There is a particular edge case when the pack is charged to 100%, the TC bit is set but the overcurrent discharge protection gets tripped (without clearing TC). When voltage is applied to the charger circuit, the pack receives the initial pre-charge (~75mA). However, because the TC bit is set and the pack is in charge mode, the TCA bit sets and the alarm shuts down the charger before the OCD condition can clear (8 second recovery delay). Naturally, the TC bit cannot be cleared in this state since discharge is disabled by the OCD protection.

The TCA bit stays high for about 30 seconds and during that time the alarm goes off every 10 seconds. After the initial charger shutdown, if power to the charger is re-connected at the right time, the precharge current can clear OCD before the 10 seconds is up. However, considering that the first application of the charger will always initiate the TCA and fail to clear OCD, having the customer disconnect and reconnect charger power to recover a pack in this state is a less than elegant solution.

There is the option of increasing the Chg Current Threshold to 100mA so precharge will not set the pack to charge mode, but this will affect other protections. An example that I gathered from section 2.8 of the bq40z50-R1 TRM is that the over/under temperature charge protections would not be enabled for the 75mA precharge.

The simultaneous TC and OCD condition seems to be a general issue with the bq40z50 talking with a smart charger over SMBus. Does TI have recommendations on how to address this edge case?

Regards,

Andrew Elgar

  • 0
    TI__Mastermind 42535 points
    Your thread has been assigned to me, I'll look into it and reply today.
  • 0 in reply to Batt
    TI__Mastermind 42535 points
    You can actually reduce the OCD Recovery Threshold to 60mA which would still be above chg current threshold. That combined with reducing your OCD recovery delay can fix this.
  • 0 in reply to Batt
    TI__Mastermind 42535 points
    I see that you have marked this as not resolved. Can you please explain why? Have you attempted this solution?
  • 0 in reply to Batt
    Prodigy 110 points

    I have attempted the solution. I had forgotten to mention that the OCD recovery current was already 40mA. Reducing the OCD recovery time does not solve the problem unless the recovery time is 0 seconds. Attached is a log file demonstrating that the TCA alarm will shut off the charger when first applied, even with the recovery delay set to 1 second (lines 14-18). The current spikes at lines 38-46 and lines 60-73 are when I disconnect and reconnect voltage to the charger circuit. Even with a 1 second delay, it is still a race condition that took multiple attempts to recover the pack.

    Fullscreen TC_OCD_1s_recovery.log Download 
    Data Log

TimeStamp,Current,Gauging Status,Battery Status,Recovery Threshold,Recovery Delay,Safety Status A+B,
2018-07-31 06:11:15,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:15,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:15,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:16,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:16,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:16,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:16,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:17,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:17,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:17,0,0x5A,0x00E0,40,1,0x0010,
2018-07-31 06:11:19,75,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:19,42,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:19,22,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:20,5,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:20,5,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:20,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:20,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:20,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:21,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:21,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:21,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:23,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:23,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:23,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:24,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:24,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:24,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:24,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:25,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:25,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:25,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:25,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:27,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:27,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:27,9,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:28,9,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:28,29,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:28,48,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:28,67,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:29,77,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:29,69,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:29,58,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:29,38,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:31,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:31,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:31,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:32,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:32,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:32,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:32,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:33,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:33,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:33,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:33,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:35,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:35,0,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:35,9,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:36,9,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:36,29,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:36,49,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:36,68,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:37,78,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:37,76,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:37,76,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:37,77,0x1A,0x40A0,40,1,0x0010,
2018-07-31 06:11:39,78,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:39,48,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:39,29,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:40,29,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:40,9,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:40,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:40,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:41,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:41,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:41,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:41,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:43,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:43,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:43,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:44,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:44,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:44,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:44,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:45,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:45,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:45,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:45,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:47,0,0x1A,0x40A0,40,1,0x0000,
2018-07-31 06:11:47,0,0x1A,0x40A0,40,1,0x0000,

  • 0 in reply to Andrew Elgar
    TI__Mastermind 42535 points
    Thanks for checking the solution out. I will be able to look into this in the next few days. Please give me until Tuesday to check some solutions out for you and to confer with the fw engineers if this is actually a corner case.
  • 0 in reply to Batt
    TI__Mastermind 42535 points
    I think I have a solution for you. In the gauge settings under SOC Flag Config A reset TCCLEARRSOC and set TCCLEARV. Similarly under SOC Flag Config B, reset FCCLEARRSOC and set FCCLEARV. Under the gas gauging tab, change the voltage for TC and FC to 4150mV. This way if you experience an overcurrent during dsg, you will have at least cleared TC and thereby closed your chg fet.
  • 0 in reply to Batt
    Prodigy 110 points

    I've had success with a variant of your suggestion. I still need TC & FC to clear by SOC but I've also set the TCClearV bit and used a lower voltage threshold of ~4.0V. While I need to do more testing, TC Clear at 4.0V should only matter during overcurrent discharge at TC/FC state. Otherwise, for normal discharging, TC will clear by SOC% before a cell gets to 4.0V. Thank you for your assistance.