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BQ2970: External sense resistor

Guillaume Levant34
Intellectual 320 points
Part Number: BQ2970
Other Parts Discussed in Thread: BQ2980

Hi,

I am looking for a battery protection that protect against overcurrent at 100mA.

The BQ2970 seems interesting, but I don't think I can find FETs with RDSon high enough in order to trigger the overccurent protection as low as 100mA. So would it be suitable to add a sense resistor in series with  the FET between V- and VSS in order to set the overcurrent thresholds to 100mA ?

Best regards,

Guillaume

  • 0
    TI__Guru* 77353 points

    Hi Guillaume,

    I think this thread might be apply for your question: https://e2e.ti.com/support/power-management/f/196/t/931900

    The BQ2980 might be a better fit if it meets your needs.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 320 points

    Hi Matt,

    Thank you for your answer. My issue with the BQ2980 is that the Overvoltage threshold is pretty high for my application. I use a 4.2V battery, so 4.3V minimum OVP threshold is already quite high.

    Also with the OCC threshold is 4mV and the OCD voltage is 14mV, which is more than 3 times higher than the OCC threshold, which cannot meet the design requirement : I need a OCC current between 50mA and 100mA, and an OCD current between 80mA and 100mA.

    The BQ29707 instead would be able to fit the requirement if I can add a series resistance around 900mOhms in series with the FETs.

    Best regards,

    Guillaume

  • 0 in reply to Guillaume Levant34
    TI__Guru* 77353 points

    Hi Guillaume,

    I do not recommend using a series resistor since I have not seen this implemented before and we do not have characterization data to verify the performance. I think one issue is the FET resistance may vary with temperature differently than the resistor. 

    Depending on your application volume, a new BQ2980 part number could be a possibility since the device is factory programmable. Do you have a local TI sales representative you can reach out to if this is an option?

    Regards,

    Matt