Other Parts Discussed in Thread: BQ76930, BQ76942
We are using BQ77PL900 for 6 cell Li-Ion battery management but facing some issues of cell balancing in standalone mode.
Configuration Settings are as follows:
No of Series cells – 6
Over voltage Detection – 4.2V (Same as balancing start voltage as per datasheet)
Over voltage Hysteresis – 0.1
Under Voltage Detection – 2.9V
Under voltage Hysteresis – 0.2V
External current path (FETs and 11 Ohm resistor) with 1K series resistors used for balancing
The voltages of cell are the next:
1 cell (the lowest) - 4,083V
2 cell - 4,101V
3 cell - 4,182V
4 cell - 4,158V
5 cell - 4,187V
6 cell (the highest) - 4,205V
The problem is that BQ77PL900 try to balance first cell, which is out of range Vov - Vovh.
The IC balances 1 b 4 cells simultaneously, then it balances 2 and 5 cells, then 3 and 6 cells...
After such balancing bataries bacame much more unbalanced then it was at the beginning.
Why does this problem appear? Or this is normal operating mode for BQ77PL900?
Schematic is the same as EVM board (file is attached).
Nb! Diodes VD2 - VD7 are not soldered.