During PWM operation of the external half-bridges, the turn-on and the turn-off of the active MOSFETs cause a significant variation of the drain-source voltage (VDS) from about ~VS to ~ GND and from ~GND to ~VS. Therefore in some applications, the turn-on and turn-off time of the active MOSFET must be long enough to limit the electromagnetic emission (EME).
In contrast the turn-on and turn-off of the freewheeling (FW) MOSFETs cause only a small variation of VDS. This variation is equal to the forward voltage of the body diode of the MOSFETs. Therefore the turn-on and turn-off phases of the FW MOSFET can be shorter, without significant penalties in terms of EME.
The different turn-on and turn-off times of the FW and of the active MOSFETs requires a separate setting for the cross-current protection time and blank times for the FW and for the active MOSFETs.
