SLUUBY1B December 2020 – April 2022 BQ76942
The BQ76942 device coulomb counter ADC measures the differential voltage between the SRP and SRN pins to calculate the system current. The device includes the optional capability for the customer to calibrate the coulomb counter offset and current gain on the production line.
The Calibration:Current Offset:Board Offset configuration register contains an offset value in units of 32-bit coulomb counter ADC counts / Calibration:Current Offset:Coulomb Counter Offset Samples. The value of Calibration:Current Offset:Board Offset / Calibration:Current Offset:Coulomb Counter Offset Samples is subtracted from the raw coulomb counter ADC counts, then the result is multiplied by Calibration:Current:CC Gain and scaled to provide the final result in units of userA.
The BQ76942 device uses the Calibration:Current:CC Gain and Calibration:Current:Capacity Gain configuration values to convert from the ADC value to current. The CC Gain reflects the value of the sense resistor used in the system, while the Capacity Gain is simply the CC Gain multiplied by 298261.6178.
Both the CC Gain and Capacity Gain are encoded using a 32-bit IEEE-754 floating point format. The value of CC Gain is given by:
| CC Gain = 106× VREF2 / (5 × 32768 × Rsense in mΩ) |
The nominal value of CC Gain using the typical value of VREF2 = 1.24 V is given by:
| CC Gain = 7.5684 / (Rsense in mΩ) |
To optimize the current measurement reported by the device, the value of CC Gain can be modified on the customer production line to match the actual value of VREF2 in a particular device.