Tool/software:
Hello all,
We use a 10S3P Li-Ion battery pack (36V) connected to the BQ77PL900 and we are facing a problem with the chip. When everything works fine the pin 29 IOUT signal is described below:
IOUT = 1.3 V in ON mode while I_load <= 100 mA
IOUT = 2.4 V when I_load = 15 A
IOUT = 1.1 V when I_load = - 2 A (means charging the battery)
After assembly we find a high failure rate of 20 % where the pin 29 IOUT signal is described below:
IOUT = ~ 2.7 V in ON mode while I_load <= 100 mA
IOUT = 3.4 V when I_load = 15 A
IOUT = 2.4 V when I_load = - 2 A (means charging the battery)
The datasheet says that V_IOUT = 1.2 V is the typical value and it's correct for most of our assemblies.
I suggested the failure occurs during our assembly process when the cell voltages VC1 - VC11 are connected to the BQ77PL900 without a GND connection so I advised the workers always to connect GND before the VC1 - VC11 voltages, but the error still occurs the same way. Also I couldn't reproduce the error, it just happens during mass production and it only happens either during the first connection of the battery pack or during the first start of the device. Because of this (even it seems unlikely) it could also be possible that the chips come already defective from the manufacturer?
After removing a defective part and replacing it with a new one, everything works just fine with the same PCB and FW and setup.
Please let me know if you have ever heard about a similar behaviour.
We are sure to use components from trusted sources like mouser or arrow but right now everything we can do is produce the PCBA, test it and rework all the faulty parts which cost us a lot of time and money.
Also we have the PCB assembled by different manufacturers and from all of them we find this exact same failure.
Is it possible that the defective parts come directly from TI? Is it possible to send a reel of BQ77PL900 components to TI to check all the chips so we would know that they are OK? I can also provide you as much defective parts as you like to run some test with them, just let me know.
Attached you can find the relevant schematic, I'll provide the whole schematic or layout per direct message if needed.
BMS Controller 3.0.Sx - Schematics v11.pdf
Any help or comment is much appreciated, thank you in advance!
Best regards
Max
