SLUA857A December 2017 – September 2022 BQ27426
The internal voltage divider in the bq27426 is factory-calibrated to have a 1-mV accuracy. The external voltage divider requires additional calibration.
For calibration, a calibrated voltage meter with resolution better than 1 mV is used. Apply a constant 8 V to the positive input of the voltage divider and read the voltage measured by the bq27426 gauge. The expected voltage should be 4 V. The difference is the offset error, and it can be stored in data flash inside the gauge.
To further investigate the impact of temperature and input voltage on the voltage divider offset and gain, a bq27426 for 2-S reference design evaluation module is built with this voltage divider circuit. Test is implemented with voltage input from 8.4 V down to 6 V with 200-mV increments at –10°C, 25°C and 50°C. The voltage measurement error across the temperature and voltage range after calibration is shown in the following table. The maximum voltage error due to the voltage divider is in the 1- to 2-mV range after calibration.
| –10°C | 25°C | 50°C | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Pack Voltage | Divided Voltage | Abs. Error | After Cal. Error | Pack Voltage | Divided Voltage | Abs. Error | After Cal. Error | Pack Voltage | Divided Voltage | Abs. Error | After Cal. Error | ||
| 8.401 | 4.193 | 0.015 | –0.001 | 8.401 | 4.192 | 0.017 | 0.001 | 8.401 | 4.192 | 0.017 | 0.001 | ||
| 8.201 | 4.093 | 0.015 | –0.001 | 8.201 | 4.092 | 0.017 | 0.001 | 8.201 | 4.092 | 0.017 | 0.001 | ||
| 8.000 | 3.992 | 0.016 | 0.000 | 8.000 | 3.992 | 0.016 | 0.000 | 8.000 | 3.992 | 0.016 | 0.000 | ||
| 7.800 | 3.893 | 0.014 | –0.002 | 7.800 | 3.892 | 0.016 | 0.000 | 7.800 | 3.892 | 0.016 | 0.000 | ||
| 7.600 | 3.792 | 0.016 | 0.000 | 7.600 | 3.792 | 0.016 | 0.000 | 7.600 | 3.792 | 0.016 | 0.000 | ||
| 7.400 | 3.693 | 0.014 | –0.002 | 7.400 | 3.692 | 0.016 | 0.000 | 7.400 | 3.692 | 0.016 | 0.000 | ||
| 7.200 | 3.592 | 0.016 | 0.000 | 7.200 | 3.592 | 0.016 | 0.000 | 7.200 | 3.592 | 0.016 | 0.000 | ||
| 7.000 | 3.492 | 0.016 | 0.000 | 7.000 | 3.492 | 0.016 | 0.000 | 7.000 | 3.492 | 0.016 | 0.000 | ||
| 6.800 | 3.392 | 0.016 | 0.000 | 6.800 | 3.392 | 0.016 | 0.000 | 6.800 | 3.392 | 0.016 | 0.000 | ||
| 6.600 | 3.292 | 0.016 | 0.000 | 6.600 | 3.292 | 0.016 | 0.000 | 6.600 | 3.292 | 0.016 | 0.000 | ||
| 6.400 | 3.192 | 0.016 | 0.000 | 6.400 | 3.192 | 0.016 | 0.000 | 6.400 | 3.192 | 0.016 | 0.000 | ||
| 6.200 | 3.093 | 0.014 | –0.002 | 6.200 | 3.093 | 0.014 | –0.002 | 6.200 | 3.092 | 0.016 | 0.000 | ||
| 6.000 | 2.993 | 0.014 | –0.002 | 6.000 | 2.993 | 0.014 | –0.002 | 6.000 | 2.992 | 0.016 | 0.000 | ||
| Unit: volts | |||||||||||||