Hello,
I'm a university student trying to build a BMS using the BQ76930 AFE and the BQ78350-R1 Fuel Gauge. I built it based on the EVM schematic and recently started to test. Hint: It's not working!
**Problem**
When I hit boot, it looks like the source follower FET (BSS138) gets very hot and the BQ76930 heats up as well. I can't seem to figure out what is wrong, and after double checking it doesn't look like I have shorted anything. Note that I have also tried bypassing the FET and applied voltage at the SRC as well, just in case it was only a FET sizing problem. The FET was obviously off, but the BQ AFE was still heating up.
If you find any other issues, I would be very appreciative. I'm pretty new at all of this.
Question: If I wound up only using only AFE would there be any good way to check for a low battery? It doesn't have to be exact either, just a general *charge this soon*. I suppose maybe getting the cell voltages might give a general idea?
I would like to hear that the chip is bad and I should just replace it and it would work but I'm pretty sure there is some type of user error here. Any help would be appreciated!
I posted EAGLE brd/sch files, apologies I'm not using anything more robust/common to industry.
**Measured Values**
The battery pack is currently sitting at 40.5V (10s Lipo 5000mAh)
At rest:
CELL10: 41V
CELL9: 36.8V
CELL8: 32.7V
CELL7: 28.5V
CELL6: 24.4V
CELL5: 20.5Vx2
CELL4: 16.5V
CELL3: 12.6V
CELL2: 8.4V
CELL1: 4.21V
CELL0: 92mV
BAT - 40.6
CAP2- 20.1V
TS2 - 20.1V
V5X - 20.1V
REGSRC - 19.6V
REGOUT - 0V
CAP1 - 0V
SCL/SDA - 0V
Source Follower
(BQ OFF):
G = 20V, D = 40.9V, S = 19.7V
(BQ BOOT):
G = 19.8V, D = 32V, S = 19.6V,
Off (100ohm, Drain): Resistor Voltage = 84mV,
Boot-On: Resistor Voltage = 3.92V
Current from Source Follower = 3.92/100 = ~40mA. This seems way too high. Tested that both the BQ and the FET are getting hot.
**Schematics**