SLUUCI8 November 2023 BQ76905
If the BQ76905 device is used in a system with fewer than 5 series cells, specific cells must be used for connection to real cells, as shown in Table 5-8. Short out the unused cell inputs on the circuit board. The device only measures and reports those cells designated as real cells. For example, if only two cells are used (which requires cell-1 connected between VC1 - VC0, and cell-2 connected between VC5 - VC4A), the 0x12 Cell 1 Voltage() command reports the lower cell voltage, while the 0x14 Cell 2 Voltage() command reports the upper cell voltage.
Number of Cell Used (Vcell Mode setting) | Cell Connections | Shorted Cells |
---|---|---|
0, 1, or ≥ 5 | VC5‒VC4A, VC4B‒VC3A, VC3B‒VC2, VC2‒VC1, VC1‒VC0 | VC4A‒VC4B, VC3A‒VC3B |
4 | VC5‒VC4A, VC4B‒VC3A, VC2‒VC1, VC1‒VC0 | VC4A‒VC4B, VC3A‒VC3B, VC3B‒VC2 |
3 | VC5‒VC4A, VC2‒VC1, VC1‒VC0 | VC4A‒VC4B, VC4B‒VC3A, VC3A‒VC3B, VC3B‒VC2 |
2 | VC5‒VC4A, VC1‒VC0 | VC4A‒VC4B, VC4B‒VC3A, VC3A‒VC3B, VC3B‒VC2, VC2‒VC1 |
Short the unused cell input pins to adjacent cell input pins, as shown in Figure 5-1.
It is also important to note that the range of voltages supported by the different VC pins differs depending on the pin. For example, pins VC5, VC4A, and VC4B can only support measurements if their pin voltage is greater than or equal to 2 V. Thus if implementing a 2s system using the top and bottom cell input pins, the upper cell voltage is not measured correctly if the lower cell voltage drops below 2 V, because then VC4A is below 2 V.
The Settings:Configuration:Vcell Mode data memory setting 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 which are not used. Voltage measurements are reported in 16-bit format (in units of mV) only for inputs used for real cells.