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Original question:

BQ27742-G1: TS measurement

BQ27742-G1: TS Sampling turns on DSG FET?

John Newell
Intellectual 280 points
Part Number: BQ27742-G1
Other Parts Discussed in Thread: BQ25890

TR 2.2.2.2.1.3 suggests that the unit should go into ANALOG SHUTDOWN if the UVP is set and no charger is detected. What is happening is that at intervals of exactly 3 seconds, the DSG FET is re-enabled. This corresponds to the TS sampling. Enabling the DSG FET results in further depletion of the battery. The UVP is the default 2800mV, and the battery is currently at 2603mV. If you allow the unit to continue in this mode, the BQ27742 does eventually shutdown.

Issuing a shutdown command immediately stops the TS sampling and DSG FET enabling ( as expected ).

I should add that the only connection between the pack+ and the system is the BAT pins on the BQ25890 charging/power chip. There is no power being applied to the BQ25890 but is the BQ27742 incorrectly determining that a charger is connected?

Bug or by design?

John Newell

  • 0
    TI__Guru* 76230 points
    Hi John,
    What is your charger detection threshold set to in the gauge data flash?
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 280 points

    Hi Onyx,

    If you could point me in the direction of the register which has a value for the charger detection threshold I could answer your question. I looked at the functional block diagram and concluded that there is a hardware comparator which detects a condition where PACKP is 300mV more than VPWR. This appeared to be the check on whether a charger is connected or not.

    There appears to be a solution to the problem, which if you could confirm would work.  Register 68 Shutdown V has default value of zero, which suggests that if I set it to a value which represents a minimum battery voltage in a worst case, the BQ27742 would no longer pulse the DSG FET..

    Incidentally, has there ever been a resolution to the problem that the Parameter Q&A gives the error 'Load or Store Action can't find the parameter: Gas Gauging.IT Cfg.Reserve Energy' I am using BQ Studio 1.3.80, and successive updates have always had this error.

    The BQ27742 is undoubtedly a very clever piece of hardware/firmware design and so please forgive me if I have overlooked something obvious.

    Regards

    John Newell

  • 0 in reply to John Newell
    TI__Guru* 76230 points
    Hi John
    You are right on the hardware comparator. I thought that parameter existed on this gauge but it is for a different one. The method with the shutdown V would work, pls try it.

    The parameter Q& A is ccurrently broken, there is no reserve energy parameter on this gauge. Did the other parameters you changed work using the q& A. If it didn't, i would suggest manually going in to the df and making the changes.

    thanks
    Onyx