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bq77910A polling question

Joe Perino
Intellectual 640 points
Other Parts Discussed in Thread: BQ77910A

We have prototyped and are considering a stacked 77910A solution to provide protection for a 16s design. The 16s battery pack in the end application can also be in parallel with other 16s battery packs.  Our customer would like to be able to periodically retrieve safety information, using a host microprocessor, from each of the 16s packs in parallel.

We understand that it is not recommended to poll the status register during normal operation of the devices; however, we would like to consider a scenario in which it might be feasible to periodically (twice an hour, twice a day?) drive ZEDE to allow the host micro to read the fault status register.  Can someone outline risks and potential issues associated with reading the status register during operation?  False safety events?  Loss of protection during polling?  Polling the register after a suspected safety event has occurred?  Loss of safety information during the register read?  And what is the minimum time required to retrieve data from the safety status register?  I have reviewed various threads and understand various issues related to noise, etc. but would like to try to understand better.  I do not want to post additional details regarding our application in the forum, so would be OK taking the conversation offline.

Thanks,

Joe Perino

Nova Battery Systems 

  • 0
    TI__Guru 54715 points

    Reading the status registers requires setting ZEDE high which minimizes all protection delays.  The temperature measurement delay is also minimized so the device current goes up due to the high duty cycle of the thermistor power.  Protections continue to run with ZEDE high, but with minimized delays, false faults are possible.  With ZEDE, SCL, SDA, VTSB swinging 3.3V and mV threshold levels likely on the current sense, noise in the system, internal or external to the IC or system which aligns with samples can trip a fault.  OV or UV faults would require the cell voltages to recover through the hysteresis settings to recovery. Current faults would require the appropriate recovery conditions. Temperature faults would need to recover through the hysteresis.

    The part was not intended to have the status read during normal operation and it is not recommended for normal operation.  The status registers are not in the datasheet.

    In evaluation, if a false protection is triggered while reading status, the test can likely be repeated and the spurious fault filtered.  In system this could be much more difficult and may not be acceptable.  The bq77910A was designed as a standalone protector.  For systems where communication with the device is required in system, an AFE type function is desired.