BLDC Motor system IC TLE9563/TLE9564- Why are the setting of charge and discharge currents of the freewheeling and active MOSFETs different?
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 for a good 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.
That is the reason why the charge and discharge currents of the FW MOSFETs can be configured independently from the charge and discharge currents of the active MOSFETs.