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BQ20Z45-R1: SMBUS communication delay

Thomas CN1
Intellectual 300 points
Part Number: BQ20Z45-R1
Other Parts Discussed in Thread: BQ20Z655-R1, BQ24765

Hello,

We have a battery pack using BQ20Z45-R1 gas gauge. We read the battery parameters every 2 seconds via SMBUS. Our software typically completes the read operation of battery parameters within 55 to 60 milliseconds. But randomly the read operations takes more time than 200mS and even seconds some times. This causes our software to go into communication timeout. Any  lead to the reason for this behavior is appreciated. It is very random in nature and not easily reproducible, hence we are unable to probe the signals and look into the issue.

There is bus timeout condition tTIMEOUT mentioned in data sheet as 25uS to 35uS. The note is "The bq20z655-R1 times out when any clock low exceeds t(TIMEOUT)". Is this timeout has any possible relation for this communication delay.

Important: We have the smart battery charger BQ24765 also connected to same SMBUS.

Any suggestion to debug this issue is highly appreciated

Regards,

Thomas CN

  • 0
    TI__Guru** 105590 points

    Hello Thomas,

    The gauge can clock stretch or NACK a command when it is processing data like lifetime information. If the gauge ACKs it's device address and NACKs the command it is most likely busy with internal calculations/DF writes.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 300 points

    Hi Wyatt Keller,

    Thanks for the reply. Can you please also give more information on the bus timeout condition tTIMEOUT mentioned in data sheet as 25uS to 35uS. The note is "The bq20z655-R1 times out when any clock low exceeds t(TIMEOUT)". Is this timeout has any possible relation for the communication delay? Also if the timeout is 35uS max, then how it is possible to have communication at the lowest speed 10KHz mentioned in data sheet? 10KHz will have a clock low time of 50uS and that can cause timeout, right?

  • 0 in reply to Thomas CN1
    TI__Guru** 105590 points

    Hello Thomas,

    This may be a typo in the datasheet for TIMEOUT. The specification and all newer gauges (which adhere to the same specification) use 25ms to 35ms.

    Sincerely,

    Wyatt Keller