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BQ40Z50-R2: NC pins and thermistor readings

H P
Prodigy 40 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50

Tool/software:

Hello,

We have a design that uses the BQ40Z50 with R5 firmware.

We found some strange behavior with the external thermistor: the reading would not go below -20C.

After comparing with the EVM, which works, we tried grounding the NC pins of the BQ40Z50 in our design (they were floating before).

Now the temperature reading works as it should.

Does this NC-pin fix seem reasonable?

Or could it be that we have another issue that just happened to stop when we did this?

  • 0
    TI__Mastermind 28440 points

    Hello,

    If possible, please share the schematic of the gauge design so we can take a deeper look into this.

    Regards,

    Anthony

  • 0 in reply to Anthony
    Prodigy 40 points

    86023.Schematic.pdf

    See attached PDF for the schematic. The NC pins were grounded with jumper wires, so they are unconnected in the schematic.
    The thermistor is connected between pin 5 and 6 in connector J1.

  • 0 in reply to H P
    TI__Mastermind 28440 points

    Hello,

    Understood, thank you for sharing. Since the NC pins are grounded in the bq40z50-EVM design, then I believe this should be done in the current design as so. In the design, is the 0 Ohm resistor between the negative side of the cell connection and ground DNP'd?

    Regards,

    Anthony

  • 0 in reply to Anthony
    Prodigy 40 points

    Yes, that was my conclusion also.

    I would like some verification that the NC-pins are a probable reason for the issue.
    It is an important function that was not working and we need to be sure that it will not break in the future.
    Do you have any information about how the NC-pins are connected internally?

    Yes, the 0 ohm is DNP. The GND and BAT- are connected at the cells.

  • 0 in reply to H P
    TI__Mastermind 28440 points

    Hello,

    Would it be possible to share the .gg file for us to check the rest of the temperature configurations?

    Regards,

    Anthony

  • 0 in reply to Anthony
    Prodigy 40 points

    4810.Export.gg.csv

    Yes. See attached. The NTC we are using is ED2F103A2-91007.

  • 0 in reply to H P
    TI__Mastermind 28440 points

    Hello,

    Thank you for sending the .gg file, it seems like the temperature configurations are set correctly. Is there any difference to this behavior (while NC is not grounded) if the TInt is disabled in the Temperature Enable register leaving only the TS1 measurement?

    Regards,

    Anthony

  • +1 in reply to Anthony
    Prodigy 40 points

    Hello again, this issue was solved now and it was not related to the grounding of the NC-pins.

    The measurements and modifications of the PCBA were mixed up and the change that made the difference was not when we added ground but when we removed capacitance from the TS1 pin.

    The temperature measurement is pulsed and the capacitance that was placed on the TS1 pin made the pulse so slow that it could only reach to the value -20C during the pulse time.

    We removed some capacitance and now it works.

    Thanks for your help!