Silicon carbide MOSFET V_GS thresholds tend to be lower than silicon junction MOSFETs. As the temperature goes up, the V_GS threshold goes down. For example, onsemi’s NTH4L022N120M3S 1200 V, 22 mΩ silicon carbide MOSFET specifies a 2.72 V V_GS threshold at +25ºC. However, at the maximum junction temperature of +175ºC, the V_GS threshold can drop as low as 1.5 V. This low V_GS threshold can be an issue during turn-off because the V_GS can experience some ringing around 0 V, accidently turning on the silicon MOSFET during turn-off, which is a bad thing. To mitigate against this issue, the gate driver offers negative bias during turn-off. So instead of the V_GS stopping at 0 V during turn-off, the gate driver turns off below 0 V; then any ringing will not trip the V_GS threshold. The NCP51561 supports a negative bias voltage as low as minus 5.1 V.