If the BQ76922 device is used in a system with fewer than 5-series cells, the additional cell inputs can be utilized to improve measurement performance. For example, a long connection may exist between two cells in a pack, such that there may be significant interconnect resistance between the cells, such as shown in Figure 4-1 between CELL-A and CELL-B. By connecting VC2 close to the positive terminal of CELL-B, and connecting VC3B close to the negative terminal of CELL-A, more accurate cell voltage measurements are obtained for CELL-A and CELL-B, since the I·R voltage across the interconnect resistance between the cells is not included in either cell voltage measurement. Since the device reports the voltage across the interconnect resistance and the synchronized current in DASTATUS1–2(), the resistance of the interconnect between CELL-A and CELL-B can also be calculated and monitored during operation. It is recommended to include the series resistance and bypass capacitor on cell inputs connected in this manner, as shown below.

Figure 4-1 Using Cell Input Pins for Interconnect Measurement

If this connection across an interconnect is not needed (or it is preferred to avoid the extra resistor and capacitor), then the unused cell input pins should be shorted to adjacent cell input pins, as shown in Figure 4-2 for VC3B.

Figure 4-2 Terminating an Unused Cell Input Pin

The Settings:Configuration:Vcell Mode configuration register is used to specify which cell inputs are used for actual cells. The device uses this information to disable cell voltage protections associated with inputs that are used to measure interconnect or are not used at all. Voltage measurements for all inputs are reported in a 16-bit format (in units of mV) as well as a 32-bit format (in units of raw ADC counts), irrespective of whether they are used for cells or not.