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BQ78350-R1: What's the accuracy of protection delay time?

joy zhou
Intellectual 565 points
Part Number: BQ78350-R1

Hi,

We have a 5s BMS project which is using BQ7692000PWR+BQ78350DBTR-R1.The circuit board is working well except protection delay time.

For example, In the protection COV delay time configuration, the setting is 2s, the real action delay timing is around 3s; the setting of protection OCD delay time is 2s, but the real action delay time is around 4s.

My customer sent me below questions and need me to reply:

  1. Why is the timing so far off? 
  2. Is this a problem with this battery or all batteries and what are guaranteed times?

Could you please help me to know the below answers:

1) Why is the timing so far off?

2) What are guaranteed times?

Thank you very much!

Joy

  • 0
    Intellectual 565 points

    Hi,

    Can any one help to answer my above questions? My customer is still waiting for my reply.

    Thanks,

    Joy

  • 0 in reply to joy zhou
    TI__Guru 73830 points
    Joy,
    I will have to bench test it to see how much it is off. The AFE responds to the fault and takes action and then reports it to the gauge. The gauge can then try reporting and clearing the fault.

    Tom
  • 0 in reply to ThomasCosby
    Intellectual 565 points
    Hi Tom,

    Thank you for your help and waiting for your answer.

    Thank you very much!
    Joy
  • 0 in reply to joy zhou
    Intellectual 565 points

    Hi Tom,

    My manager and PM will have a call with our customer this afternoon at 2 pm(eastern time), they need to provide an answer for this to our customer. Could you please give an updated how's your testing result and how's the accuracy of protection delay time?

    Thank you very much!

    Joy

  • 0 in reply to joy zhou
    TI__Guru 73830 points

    The firmware based over-current protection feature uses the coulomb counter interface to measure the current. The coulombs are accumulated continuously and converted every 250ms. The four 250ms samples are averaged together and reported every 1s, so there is at least 1s latency associated with that. In addition, depending on where the current increase occurs within the cycle, it may not be at a high enough magnitude to trip the protection threshold and then the gauge has to command the AFE to turn the FET off after the programmed delay time. You will find that the delay will vary with the magnitude of the current with respect to the over-current thresholds.


    The firmware based voltage protection feature work in the same manner, except that the voltage is not accumulated continuously. It is sampled one time every 250ms and the four samples are averaged and reported every one second. There will also be latency in the delay timing depending on where the over voltage condition occurred in the sampling cycle and the magnitude of the over voltage condition. 

  • 0 in reply to ThomasCosby
    Intellectual 565 points
    Hi Tom,

    Thank you very much for your reply.

    Then in my understanding, the worst condition of the delay time( over current and voltage) will be the setting protection delay time + 2s. Please confirm whether this is correct.

    By the way, for a temperature protection, will be the same, 2s?

    Please confirm.

    Thank you very much!
    Joy
  • 0 in reply to joy zhou
    TI__Guru 73830 points
    That expected delay variance is correct and the same applies to temperature faults.
  • 0 in reply to ThomasCosby
    Intellectual 565 points
    Hi Tom,

    Got it.

    Thank you very much!
    Joy