Broadcom ACPL-355JC Reference Manual page 22

ACPL-355JC Reference Manual
Figure 15: Driver Behaviors during an Over-Current Event
In the current design, the threshold voltage is set to 2.5V. This means that the OC protection will react after the MOSFET
drain current reaches approximately 600A for the selected MOSFET at an ambient temperature of 25°C.
The freewheeling of the antiparallel diodes connected across the MOSFET can have large instantaneous forward voltage
transients. This may result in a large negative voltage spike on the OC pin, which will draw substantial current from the driver
if protection is not used. Limiting this current is done via a 1-kΩ resistor placed in series with the OC diodes.
Negative voltage spikes typically generated by inductive loads or reverse recovery spikes of the IGBT/MOSFET
freewheeling diodes can bring the OC pin voltage above the threshold, thus generating a false fault signal. To prevent this,
Zener and Schottky diodes are placed across the OC and V
transient voltage, and the Schottky diode prevents forward biasing of the substrate diode of the gate driver optocoupler.
Table 11 provides the recommended Zener diode voltage values for the WAB300M12BM3 and FF6MR12KM1 MOSFET
modules.
Table 11: Recommended Values for Zener Diode Cutoff Voltage
Device
WAB300M12BM3
FF6MR12KM1
Because MOSFETs are more sensitive to over-current than IGBT, the OC protection must be faster. That can be done by
tweaking the OC blanking time; thus one additional resistor R13 (R32) is added between the OC pin and V
an additional blanking capacitor charging current component from the secondary driver power supply, so that blanking time
can be shorter and can be adjusted via resistor R13 (R32).
Broadcom
pins. The Zener diode protects the OC pin from positive high
S
D2, D12
3.9V
1.8V
62-mm SiC Module EB1200M62-355JC Evaluation Board
ACPL-355JC-62mmSiC-RM100
. This allows
DD2
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