I am using bq77pl900 for balancing 8 cells li-pol pack. When I connect cells to balancer, nothing happened. After wake up with supply voltage (around 30V), device wake up, cells starts charging but after half second device go power down (even if the power supply is connected).
If I measure voltage on internal VREG1, 2 (with only BAT supply from cells), there is 0 voltage. After applying voltage to PACK pin, internal regulator start.
Please, where is the problem? Why device power off?
You will need to check the circuit with your system schematic and settings.
The device needs VI(STARTUP) of > 7.5 V (recommended) on the PACK pin to wake up. It will wake in standalone mode and if you do not transition to host mode will make decisions based on its algorithm, see figure 3 of the datasheet. If the part detects under voltage it will shut down, but default is 1 s, and if PACK is held high by a charger it should not be able to shut down. If the number of cells is set for more than you have connected, the un-used cells are under voltage.
The default OV delay is 0.5 s. Check if the device is seeing an OV, turning off the charge FET, then shutting down from UV. However the PACK pin voltage would have to be missing.
Check the voltage at the PACK pin while the charger is applied to the pack, check for broken connections as needed. It may be useful to connect to the serial interface and check its status while you hold PACK high. The status should show if you have UV, OV, both or neither.
Check for broken connections between the cells and VCx inputs to the part. If the VCx pin voltage drifts after wake-up, you may get OV, UV or both. Also check for shorted VCx to VCx+1 caused by over-voltage some time in the board assembly or test process. Measure the differential voltage at VCx pins if available, or checking the voltage across the RVCX resistors may show an unusual current into a cell input pin and out the next resulting in a low voltage on one input pair and high voltage on the adjacent ones.
If you are using zero voltage charging, check that the ZVC bit is set appropriately.
I checked it, many times. But maybe I overlooked something. Here is the circuit. I have 2 li-pol pack, each 4 cells, series connected.
When PACK is held by charger, device is running and I can read the STATUS register. But immediately when I unconnect charger, device shut down. The PCB connection is OK, no broken connections. I put an oscilloscope on XALERT pin and CHG. Here is the diagram after connecting charger.
It looks like overvoltage, but each cell has 3.65V (also on the pins of bq77pl900). When I read STATUS register (only when charger on PACK is applied) I get values 51 and 12 (it toggles). 12 means UV and OV. 51 means OCD, SCD, OVTEMP and VGOOD.It acts really very strange :(
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