As a diagnostic feature, the gate threshold voltage monitor feeds back the measured threshold voltage to the MCU to judge the health of the power transistor, as described in Figure 3-21 and Figure 3-22. This is helpful in determining system lifetime and the potential for a failure later in time. The gate threshold voltage monitor measures the actual threshold voltage of the SiC MOSFET or IGBT. When enabled, the switch between DESAT and OUTH is turned on and a constant current source charges the gate capacitance of the power transistor, causing the gate voltage to ramp up gradually. Once the transistor channel starts to conduct, the gate voltage is naturally held at the threshold voltage level as the power transistor is in a diode configuration. After the blanking time, t_dVGTHM, the integrated ADC samples the gate voltage, and reports the measurement to the ADC Data Register.

Figure 3-21 Gate voltage threshold monitoring while gate capacitor charges

Figure 3-22 Gate voltage threshold monitoring while power transistor is in diode configuration