Hi, we are using bq76940, which is capable measure 15 battery cells. We are designing a 14 cell battery pack, and so on schematic, we shorted VC13 & VC14 following the datasheet recommendation. When we calculate the pack voltage, in "section 10.3.1.1.6, 16-Bit pack Voltage", the formula given is as follows: V(BAT) = 4 x GAIN x ADC(cell) + (#Cells x OFFSET).
My question is that, given we are using 14 cells, should we use 14 as "#Cells" in the formula, or should we use 15 in the formula, since the BQ76940 also report a (small) non-zero value for the shorted cell? See the highlighted entry in the table below.
Also, on the shorted cell input VC13, we see a voltage reading of 0.0498849973 Volt. It is small but it is 49.8mV. When BQ76940 report pack voltage (using BAT_HI and BAT_LO), is this small voltage being added to the pack voltage, or is it being ignored?
From the data collected from the debugger, looks like we should be using 15 cell in the pack voltage calculation, and the value provided in the BAT_HI and BAT_LO registers does include the value from shorted VC13. Can you confirm?
| pack_voltage_V | 57.0998497 |
| adc_gain_uV_per_lsb | 377 |
| adc_offset_mV | 48 |
| raw | 37419 |
| BAT_HI | 0x92 |
| BAT_LO | 0x2b |
| Vpack w/ 14 offset | 57.099852 |
| Vpack w/15 offset | 57.147852 |
| cell voltage idx | cell_voltage_V |
| 0 | 4.07850695 |
| 1 | 4.07775307 |
| 2 | 4.08039188 |
| 3 | 4.079638 |
| 4 | 4.07662201 |
| 5 | 4.079638 |
| 6 | 4.0822773 |
| 7 | 4.082654 |
| 8 | 4.0822773 |
| 9 | 4.07888412 |
| 10 | 4.07398272 |
| 11 | 4.07850695 |
| 12 | 4.07624531 |
| 13 | 0.049884997 |
| 14 | 4.07209778 |
| sum 0~14 | 57.14936039 |
| sum 0~12, 14 | 57.09947539 |
Thanks!
