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BQ24297: BQ24297 for battery temperature sensing without adaptor plugged

Nicole Han
Intellectual 2230 points
Part Number: BQ24297
Other Parts Discussed in Thread: BQ25895M

Hi, team,

My customer want to sense battery temperature when the charger isn't charging battery, the adaptor isn't plugged in.

From the block in bq24297's datasheet, the internal voltage reference for hot/cold temperature threshold is REGN, while it comes from VBUS, that means there is no REGN output in case of no adaptor plugged, and we couldn't use an external supply voltage for temperature sensing. So we are thinking to supply the temperature sensing circuit with REGN during charing, and swich to an external supply when no charging and render the TS voltage to MCU's ADC input.

Need to check with you what's the input impedance of TS pin at bq24297 power on and power down.

And also do you think if there is other way to sense the battery voltage when no charging? Customer don't want to add cost for thermistor. Thanks!

  • 0
    TI__Mastermind 25800 points

    Hey Nicole,

    You are correct that the bias for the TS sensing is REGN, and without a VBUS, there is no REGN voltage. The TS pin is a high impedance input at both power up and power down.

    In reference to your last question, I believe you mean to say the battery temperature, not battery voltage. Am I correct in assuming this?

    If you are trying to measure battery temperature (with and without an adapter), you will need a thermistor or at least some temperature IC.

    If your customer's concern is measuring battery temperature without an adapter plugged in, one option is to put the device in OTG mode momentarily. OTG mode will provide power to REGN and give TS status. However, be sure that your customer's system can support this temporary boost mode at VBUS and PMID pins.

    If my assumption was wrong and your customer wants to know battery voltage, I suggest taking a look at the bq25895M. It is very similar from a pin and package size standpoint, but has the added feature of an internal ADC to monitor ICHG, VBAT, VBUS, and TS percentage.

    I hope this helps!

    Regards,

    Joel H