BQ76940: Rf and Cf Values

Rohan Patwardhan1

Part Number: BQ76940

Hi TI Team,

What must be the range of Rf and Cf values for BQ76940 series. We are currently using 4.7uF and 1k resistor combination. However we wish to migrate to a lower capacitance (1uF or 2.2uF)

Will this be in acceptable range? Do we need to change Rf values as well? Can there be repurcussions of a low capacitance value?

Attaching snap of datasheet for reference of Cf values.

Regards,

Rohan

over 4 years ago

0 WM5295 over 4 years ago

TI__Guru 54715 points

Hi Rohan,

See https://www.ti.com/lit/pdf/slua749 section 3. You want enough Cf capacitance and large enough Rf resistance so that along with the discharge by Rin during short circuit, the part remains awake with VC5X above the VSHUT voltage so that the part can time the SCD event and turn off the DSG FETs. See a waveform at about 7:10 in the video https://training.ti.com/getting-started-our-monitoring-and-protection-ic-high-cell-count-batteries. If the part loses power due to small capacitance it can't turn off the FETs and they will go off some ms later. 1 k ohm and 10 uF are common for Rf and Cf, you may be successful using smaller values in your specific system implementation.

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BQ76940: Rf and Cf Values