We bought a number of bq20z65evm boards that we have been using in testing. I have put one test battery thought 33 cycles of charge/discharge without any major problems, and I have done a number of cycles with loads up to 5 amps. After working a number of minor issues, we thought that we had a good configuration working, but we now have a number of boards where we have been getting PF caused by a over temperature alarms. Some of the failure have occurred with 2 amps loads, others have worked fine until we have given them a 6 amp load. We bought one of the problem batteries back to my lab and I discovered that one of the IC (I think it was the discharge FET) was overheating, causing the TS1 thermistor (they are still attached to the board) to heat up and then go over it set limit during discharge. During the last test, the discharge FET didn't seem to shut off, even though it was command to. It only seem to shut off on it own (several minutes after recording a OTA PF), and after removing the PF and resetting the board, I found that the discharge FET no longer works.
I have attachedthe GG configuration file that we use, a log file taken during the last test (3 amp discharge test), and the GG file after the test (to dump all the registers). Can you look at the files and see what going wrong? The log file is from a program I developed to dump the same values that the bqEVSW does, but it also dumps the TS1 and TS2 values (at the end of the line). All the temperature values are raw .1K values, not C, otherwise, the value dump should be the same as what bqEVSW dumps..
The only thing that I can think that might be causing our problem is how I have the precharge FET configured. I have never fully understood how the precharge FET options work with the bq20z65evm, and I found that the documentation in the bq20z65evm pdf and the bq20z65 technical document to be not very clear and the default configuration didn't do what we wanted. I found that using the default resistor configuration on the bq20z65evm board, using the ZVCHG FET, and the charge current set to 500 ma during the precharge stage, that we were only getting about 10ma of charge, which caused a very long precharge time. To get around this problem, I switched to having ZVCHG0 set to 0, ZVCHG1 set to 1 (to skip using the ZVCHG FET), but I didn't change the resistor configuration (set for 0-VChg). This work great on my test board, giving us about 500ma during the precharge stage and all of our test batteries have this configuration. Could this be causing a problem during the discharge stage and it causing the over heating problem?
Thanks and Best Regards, Tim Starr on behalf of CF@EI
