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Original question:

BQ24072: IEC-62368 certificate

BQ24072: Temperature sense required for two batteries in parallel

Srishtik Bhandarkar
Prodigy 20 points
Part Number: BQ24072

Tool/software:

Hello,

I am planning on using BQ24072 for my design and planning to get UL94V certification for my product. 
As it is required to monitor battery temperature for the certification, I am facing a bit of an issue since my design requires two lipo batteries 850mAh each to be used in parallel for increased capacity. 

I had few questions regarding this:

  1.  BQ24072 has a single TS pin and can monitor only a single cell. When I read the datasheet, I came to know that the charging is disabled in case the temperature limits (Either under temperature or Over temperature) is exceeded. Am I correct?
  2. Is there any protection when discharging if temperature limits are exceeded?
  3. As a work around for this problem, I am planning on implementing the comparator for Temperature myself for both the batteries externally and use Digital logoc to pull CE pin high if the temperature limits are exceeded on any of the batteries in parallel. Would this work for UL94V certification or has the feature be implemented on the chip itself?

Any suggestions regarding this would be appreciated.

Thanks and Regards,

Srishtik

  • 0
    TI__Expert 7920 points

    Hi Srishtik,

    Thanks for reaching out.

    Srishtik Bhandarkar said:
     BQ24072 has a single TS pin and can monitor only a single cell. When I read the datasheet, I came to know that the charging is disabled in case the temperature limits (Either under temperature or Over temperature) is exceeded. Am I correct?

    Your understanding is correct. The BQ24072 monitors the voltage on the TS pin (VTS) during charging. If VTS is outside of the normal battery temperature operating range (between VCOLD and VHOT), charging is suspended.

    Srishtik Bhandarkar said:
    Is there any protection when discharging if temperature limits are exceeded?

    No, the BQ24072 only monitors the TS voltage while charging. If you need to monitor the battery temperature at times other than just charging, I'd recommend looking into a battery fuel gauge IC.

    Srishtik Bhandarkar said:
    As a work around for this problem, I am planning on implementing the comparator for Temperature myself for both the batteries externally and use Digital logoc to pull CE pin high if the temperature limits are exceeded on any of the batteries in parallel. Would this work for UL94V certification or has the feature be implemented on the chip itself?

    The packaging for most TI parts is UL94 V-0 compliant.

    https://www.ti.com/support-quality/certifications-and-standards/certifications-home.html

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Prodigy 20 points

    Hey hi Alec,

    Actually I wanted to ask if there is any reference design where NTC from two batteries can be sensed at the same time using BQ24072? Since my application requires monitoring two batteries in parallel.

    Regards,

    Srishtik

  • 0 in reply to Srishtik Bhandarkar
    TI__Expert 7920 points

    Hi Srishtik,

    The BQ24072 monitors the TS pin voltage to determine whether the battery is in the normal operating temperature range.

    When using two cells in parallel, the simplest solution will likely be to disable the TS function and instead control charging through the /CE pin using external logic.

    If you already have an MCU in your system, you could monitor both thermistors using the MCU's ADCs, implement temperature range checks in firmware, and disable charging by pulling /CE low when either cell is outside the safe range.

    If there's no MCU, you could achieve the same result with external comparator circuitry and discrete components, though it adds some complexity. I haven't found any reference designs for that specific approach, but it should be possible to implement with the right thresholds.

    Let me know if you have any other questions.

    Best regards,

    Alec