BQ76940 - MOSFET failure during short circuit13S BMS REV-2 INTEGRATED-1.pdf
Test setup:
1. Battery spec - 26 Ah, 54 V fully charged battery
2. SC threshold - 111mV @ 50us SC delay
3. Shunt resistance - 1 mOhm
A switch is placed between the Battery+ and L-/C- in order to cause the short circuit.
Problem - discharge MOSFETs are failing during short circuit condition.
Note: We are setting both FETs OFF during the SC conditon (CHG = 0 and DSG)
During the SCD condition, MOSFETs are taking 500us to turn off. Is this delay causing FETs to go out of the SOA, which might be causing the FETs to fail?
Also, how do we estimate the SCD threshold value for different capacity battery packs?
MOSFET specifications are given below:
1. HY4008B N channel Enhancement Mosfet
2. VDSS Drain-Source Voltage 80 V
3. VGSS Gate-Source Voltage ±25 V
4. TJ Maximum Junction Temperature 175 °C
5. IS Diode Continuous Forward Current @TC=25°C 200 A
6. ID Continuous Drain Current 200A
7. RDS(ON) Drain-Source On-state Resistance @ VGS=10V & IDS=100A - 2.9 typical, 3.5 milliohm max
8. VGS threshold - 2 to 4 V
How to calculate the value of Gate resistor. Currently we are using 1k resistors.
Schematic is attached.
