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BQ76952: Soft-shutdown effect

Kyungjae Lee
Intellectual 670 points
Part Number: BQ76952

Tool/software:

Hi,

Our BMS firmware is designed to perform a full reset of the AFE during the system initialization phase to ensure a fresh start, including reloading parameters from OTP memory into the data memory registers.

However, we have recently discovered that if this reset occurs while the load is attached, the AFE fails to complete the full reset and instead enters soft-shutdown mode. This leads to unintended behavior.

To address this issue, we are considering the following two solutions:

  1. Replace the full reset sequence with a partial reset.

  2. Continue performing a full reset, but follow it immediately with a partial reset to bring the AFE out of soft-shutdown mode.

We have a few questions regarding these options:

  • For Option 1, my understanding is that a partial reset will not clear protection statuses such as Safety Status A, B, and C, is this correct?

  • For Option 2, from the AFE's perspective, what is the difference between going through only a partial reset versus entering soft-shutdown mode and then being brought back to normal operation via a partial reset? Will this process clear the Safety Status A, B, and C?

From one of the following threads I've looked into, it seems like performing a full reset or shutdown is not recommended unless you are dealing with the delivery or long-term storage mode. With that said would you recommend option 1?

Here are the resources I have already looked into:

Thank you,

Kyungjae Lee

  • 0
    TI__Expert 5100 points

    Hi Kyungjae,

    The system trying to enter soft shutdown upon a full reset just because a load is attached is not normal, I think it would be best to understand why that is occurring, and fix that.  Have you programmed your settings into OTP?  When it enters soft shutdown, are you still able to communicate with the device, to see if there are hints why it would be trying to shutdown?  Is it possible your load is causing a low cell or stack voltage, and the Shutdown Cell Voltage or Shutdown Stack Voltage settings are then causing it to enter shutdown?  FETs are normally disabled by default, do you have OTP settings that enable it?

    When the RST_SHUT pin falls, the device first does an integrity check of the static memory contents, to make sure it matches the signature stored for that content.  If it matches, the part continues to use those settings and restarts normal operation.  If the signature doesn't match, it performs a full reset.  Normally the signatures would match, but there is a slight possibility they would not match if the partial reset occurred right as the device was changing static memory contents and recalculating a new signature to store, but didn't complete saving the new signature.  This is possible but statistically very unlikely.

    I don't recall if the protection status registers are cleared by a partial reset, would need to test that on an EVM, but unfortunately I don't have one available at the moment.  You might just test that yourself on a unit if you can.

    It is also fine to use a full reset and SHUTDOWN mode in normal operation, you don't only have to use it during long term storage.  Some customers want the low power of SHUTDOWN mode during intervals when the measurements or protections do not need to operate, and they can handle the time for the device to reboot when needed.

    Thanks,

    Terry