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Original question:

BQ28Z610: Sense resistor selection, I2C interface and ESD questions

BQ28Z610: Sense resistor selection

Vu Tran27
Intellectual 445 points
Part Number: BQ28Z610

Hi,

I am in the process of choosing the sense resistor value. The datasheet says that we should use 0.001~0.003 ohm resistors, but also says that the OCD detection threshold voltage program step is 2.78mV/5.56mV and SCC detection threshold voltage program step is 11.1mV/22.2mV. If I know that my product only runs with a current in the 100mA-200mA range, would the recommend sense resistance is too small? If I use ΔVOCD to calculate the value, it would be 2.78mV/200mA = 0.014 ohm.

Thanks,

Vu

  • 0
    TI__Guru 62006 points

    A higher sense resistor is fine. Actually recommended if your currents are small. The low sense resistor is a feature because it allows high currents (e.g. for applications with large batteries and fast charging) and this is possible because of the improved performance of the coulomb counter hardware. So if you don't need that you can improve accuracy with a higher sense resistor.

    You'll have to scale all capacity and current dependent parameters if the resulting CC Gain scaling factor exceeds the maximum limit. The concept is that if you use a 10mOhm sense resistor instead of the 1mOhm sense resistor, you can leave CC Gain the same as for the 1 mOhm sense resistor but now the gauge effectively measures 10x the true coulomb count and current, hence you must manually scale all capacity (and current) parameters by 10 (e.g. a Design Capacity of 100mAh would become 1000mAh) etc.