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BQ25606: Using BQ25606 & BQ27421-G1 without a battery

Anton Ivanovsky
Prodigy 20 points
Part Number: BQ25606
Other Parts Discussed in Thread: BQ27421-G1

Tool/software:

Hi Team

I have a project that's using BQ25606 & BQ27421-G1 for Li battery charging/coulomb counting, and am wanting to completely remove the battery from the device while making minimal changes to the PCBA.

So, could you please tell me if BQ25606 & BQ27421-G1 can be used without a battery connected? From my understanding BQ25606 does not have battery detect function, so all I would need to do is pull CE high?

Cheers, Anton

  • 0
    TI__Mastermind 33885 points

    Hello Anton,

    Do you only want to have the battery removed sometime, or do you want the battery removed all the time?

    If just sometime, you should be able to put charger into charge disable with the CE pin high to disable charging. You can read the voltage from the gauge to determine when to enable charging again.

    Looking at the datasheet for the BQ27421-G1, it says that it "Supports Embedded or Removable Batteries". However, I will let someone from the gauge team confirm the setup for this.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 20 points

    I am hoping to use the same PCBA for the battery & no-battery variant of a device, so for some devices the battery will be removed all the time.

    And yup I did see that BIN pin of BQ27421-G1 can be used for battery detection (pulling BIN high via 1M8, and connecting BIN to battery thermistor output), but I'm not sure if this would mess up the thermistor reading of BQ25606 via it's TS pin?

  • 0 in reply to Anton Ivanovsky
    TI__Genius 14936 points

    Hello Anton, 

    I do not see any obvious issues with this application from the gauge's perspective. This gauge can work as a system-side gauge, meaning that it can be in a system where the battery is not permanently connected to the fuel gauge. As far as your question about this messing up the thermistor reading of the BQ25606 via its TS pin, this is a question for the charger team. 

    Regards, 

    Jonny. 

  • 0 in reply to Robert
    TI__Mastermind 33885 points

    Hello Anton,

    For R31 and R37 the device needs to see about 10k in parallel to TS to charge. However, the system will still run even if the TS voltage is wrong. You just cannot charge the battery with incorrect TS voltage.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 20 points

    Hi Mike. Thanks for the info, in that case could you please confirm if the configuration below is valid in terms of TS pin of BQ25606 being pulled to VDD of BQ27421-G1 (via 1M8 RES)? Like this won't put BQ25606 into an odd state where it's no longer operational (able to generate VSYS correctly)?

  • +1 in reply to Anton Ivanovsky
    TI__Mastermind 33885 points

    Hi Anton,

    As I said before, the SYS rail will run if the TS voltage is incorrect. To charge, please make sure TS voltage is correct.

    Regards,

    Mike Emanuel