There are two types of current faults which can be detected by the driver: overcurrent fault and short-circuit fault.
The overcurrent protection (OCP) circuit monitors drain current and compares that current signal with an internally set limit. Upon detection of the overcurrent, the LMG342xR030 conducts cycle-by-cycle overcurrent protection as shown in Figure 9-2. In this mode, the GaN device is shut off when overcurrent happens, but the overcurrent signal clears after the input PWM goes low. In the next cycle, the GaN device can turn on as normal. The cycle-by-cycle function can be used in cases where steady-state operation current is below the OCP level but transient response can still reach current limit, while the circuit operation cannot be paused. The cycle-by-cycle function also prevents the GaN device from overheating by overcurrent induced conduction losses.
The short-circuit protection (SCP) monitors drain current and compares that current signal with a internally set limit higher than that of OCP as shown in Figure 9-3. The short-circuit protection is designed to protect the GaN device from high-current short-circuit fault. If a short-circuit fault is detected, the driver turn-off is intentionally slowed down to obtain lower di/dt so that a lower overshoot voltage and ringing can be achieved during the turn-off event. On detection of an overcurrent fault, LMG342xR030 latches off. This fast response circuit helps protect the GaN device even under a hard short-circuit condition. In this protection, the GaN device is shut off and held off until the fault is reset by either holding the IN pin low for a period of time defined in the Specifications or removing power from VDD.
During OCP or SCP in a half bridge, after the current reaches the upper limit and the device is turned off by protection, the PWM input of the device could still be high and the PWM input of the complementary device could still be low. In this case, the load current can flow through the third quadrant of the complementary device with no synchronous rectification. The extra high negative voltage drop (–6 V to –8 V) from drain to source could lead to high third-quadrant loss, similar to dead-time loss but for a longer time.
For safety considerations, OCP allows cycle-by-cycle operation while SCP latches the device until reset. By reading the FAULT and OC pins, the exact current fault type can be determined. Refer to Fault Reporting for detailed information.