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[FAQ] BQ34Z100-G1: How to Calibrate Gauge at High Voltage

Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100, BQSTUDIO, BQ34Z100EVM

The BQ34z100 supports charge and discharge currents up to 32 A, pack capacities up to 29 Ah, and pack voltages up to 60 V without significant modifications. By default, the gauge ships with the configuration for a 1-series Li-Ion cell up to 4.5 V. This is handled by an internal 5:1 voltage divider with 88 KΩ in the top leg and 22 KΩ in the bottom leg. With voltages under 4.5 V, there is usually no need to calibrate the voltage, since the internal divider is calibrated during factory test to within 2 mV.

When the stack voltages exceed 5V the VOLTSEL bit in Pack Configuration should be set to tell the gauge than an external divider will be used.  Additionally, the number of series cells parameter in the data flash should be changed to the appropriate value. The divider should be designed to support the maximum expected such that the input of the BAT pin should not exceed 1 V.




The calculation for RSERIES is as follows:

The bottom leg of the divider resistor should be in the range of 15 KΩ to 25 KΩ. the example above is for the case of 16.5KΩ.  Before calibration, Set the Voltage Divider in the Data Flash Calibration section of BQStudio to the maximum expected voltage. Use BQStudio to calibrate to the applied nominal voltage here the actual gain function is determined and the resulting voltage calibration factor is stored in the data flash location Voltage Divider.

If a stack voltage of 4.5V or greater is used on the BQ34Z100EVM the 2 jumpers on J5 should be moved to the >5V slots and the appropriate voltage divider adjustments (16V,32V48V) on J2 should be made. Additionally, make sure VOLTSEL is set for external voltage divider and the number of series cells parameter in the data flash should be changed to the appropriate value.

For packs with voltages above 60V you should refer to the bq34z100-G1 High Cell Count and High Capacity Applications document.