The device is shipped with a factory configuration for the default case of the 1-series Li-ion cell. This can be changed by setting the VOLTSEL bit in the Pack Configuration register and by setting the number of series cells in the data flash configuration section.

Multi-cell applications, with voltages up to 65535 mV, may be gauged by using the appropriate input scaling resistors such that the maximum battery voltage, under all conditions, appears at the BAT input as approximately 900 mV. The actual gain function is determined by a calibration process and the resulting voltage calibration factor is stored in the data flash location Voltage Divider.

For single-cell applications, an external divider network is not required. Inside the IC, behind the BAT pin is a nominal 5:1 voltage divider with 88 KΩ in the top leg and 22 KΩ in the bottom leg. This internal divider network is enabled by clearing the VOLTSEL bit in the Pack Configuration register. This ratio is optimum for directly measuring a single Li-ion cell where charge voltage is limited to 4.5 V.

For higher voltage applications, an external resistor divider network should be implemented as per the reference designs in this document. The quality of the divider resistors is very important to avoid gauging errors over time and temperature. It is recommended to use 0.1% resistors with 25-ppm temperature coefficient. Alternately, a matched network could be used that tracks its dividing ratio with temperature and age due to the similar geometry of each element. Calculation of the series resistor can be made per the equation below.

The bottom leg of the divider resistor should be in the range of 15 KΩ to 25 K, using 16.5 KΩ:

Rseries = 16500 Ω (Vin max mV – 900 mV)/900 mV

For all applications, the Voltage Divider value in data flash will be used by the firmware to calibrate the total divider ratio. The nominal value for this parameter is the maximum expected value for the stack voltage. The calibration routine adjusts the value to force the reported voltage to equal the actual applied voltage.