Other Parts Discussed in Thread: BQ78350, , BQ76930
I have a Custom BMS which consists of bq76200 , bq76930 and bq78350 ICs. My problem is that All DSG FETs are burning while making short circuit test.
I have 7 CHG and 7 DSG parallel FETs and CHG/DSG resistors for bq76200 are 100 ohm.
I am shorting the battery for 1 second only and wait 2 minutes for the next short circuit test.
Bq78350 ascd protection is set 100 us and 268 A. However, In the third short circuit test, FETs were burned. The measured short circuit current was 1500+ A.
DSG and CHG resistor for bq76200 was 100 ohm. The charge pump cap was 4.7 uF, 100 VDC.
I also added the recommended Zener( 18V)+ series resistor ( 100 ohms) configuration between DSG and PACK pins.
In the oscilloscope, I saw the delay time for the first 2 tests. it was around 800 us which is, I think, very high.
I didn't capture the waveform of the FETs during the third short circuit test.
Below Pictures indicate the test results for different protection level For AOLD and ASCD:
DSGEN: DSG EN pin from bq76930
VGS: Gate-to-Source Voltage for DSG FETs
PACK: Battery Pack Voltage
Figure 1: Load 50 A, Disable FETs throughout Software
Şekil 2: Load 190A while AOLD is set to 170A
Şekil 3: Load is 300A while ASCD is set to 220 A
Şekil 4: Load: 230 A while ASCD is set to 220 A
Do you have any advice or past experience related to this problem?
Do you think bq76200 is not suitable for this kind of SC Ampere level ( not fast)?
Do FETs have a limit for high current switching? ( All FETs burned after 2. Short Circuit tests? )
Or What else do you think that may cause this issue?
If you further interest, I can share the schematic file via private message.
Thank you.
