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[FAQ] BQ34Z100-G1: Voltage Scaling for Odd Number Cell Counts

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

The BQ34z100 supports up to charge and discharge currents up to 32 A, pack capacities up to 29 Ah, and pack voltages up to 65 V without modifications. Using external and internal scaling the gauge can handle values above these thresholds. When working with battery configurations with currents, capacities, and pack voltages above these values there are both hardware and parameter specific considerations.

For this demonstration we will use a 17S8P pack configuration. Assume each cell has a maximum voltage of 5V and a capacity of 5500mAh. The max pack voltage becomes (17 x 5)= 85V and the capacity becomes(8 x 5500)=44000mAh which are both larger than the 65 V and 29 Ah limits the gauge can handle.  

Considerations for Voltage Scaling:

Input voltage to the BAT pin must not exceed 1V so an external divider must be implemented to support the maximum pack voltage(85V).





The value of RSERIES must be selected in order to support an 80V pack voltage. The calculation is shown below:

After hardware scaling is done the Number of Series Cells parameter must be configured in data flash as 1 cell. The calculation for the voltage divider data flash parameter in this example is as follows:

After this value is entered in the data flash the reported voltage will approximately be the single cell voltage.  Use the calibration tool in BQstudio to fine tune this divider value to obtain a more accurate single cell voltage value. Note that the host must scale the reported voltage parameter by the number of cells in order to obtain the full pack voltage. The larger the scale factor is the more resolution will be lost for gauging. Power and energy parameters should also be scaled by the host since the gauge only reports for 1 cell. For even cell counts you should refer to the bq34z100-G1 High Cell Count and High Capacity Applications document.  The notes mentioned for odd cell counts can be disregarded and this FAQ can be used for the solution.