Other Parts Discussed in Thread: BQ76PL455A
Dear TI,
I ran into a problem with BQ76PL455A BMS IC. I have designed my own PCBs based on this chip, and similar to the EVAL board, it is configurable to be used as standalone or stacked application.
All of my BMS boards work in standalone mode communicating via UART, every function is working fine, cell voltages are accurate and steady.
However, if I try to use it in stacked (Daisy-chained) mode with 2 BMSs, it seems that the top BMS is not reacting to any messages.
If I assert the WAKEUP pin of the bottom BMS, then the Wake tone appears on the differential communication, and the top BMS also wakes up (VP1, VIO, VDIG goes to 5.3V).
Then, according to the SLVA617A Software Design Reference, we send the required broadcast messages for auto-addressing. We checked the messages and every message is according to the document. However, the 2nd BMS which should have Address 1, does not respond to reading the Device Address register (0x0A).
We tried different broadcast messages, but the top BMS did not react to any of them. For example, we sent a broadcast shutdown command, and the bottom BMS went to shutdown (VP1, VIO, VDIG goes to 0V), but the top BMS was kept alive (VP1, VIO, VDIG is still 5.3V).
It seems to me that for some reason, the messages on the COMM lines are forwarded but do not make any action in the BQ76PL455A itself, and I couldn't find the reason. Could someone please help me what am I missing here?
I also checked the communication on the differential COMM lines, and the signals are nice and clean.
COMM-H output of bottom BMS:
COMM-L input of top BMS:
COMM-H output of top BMS:
