DRV8350: Current Limit question

Hi Darren,

Thank you for your question! The sink and source currents that the datasheet refers to is in regard to turning on and off the MOSFETs. To turn a MOSFET off, the driver will “sink” current from the gate of the MOSFET to the source of the MOSFET to reduce the charge on the gate to 0V. To turn on a MOSFET, the driver will “source” current from the charge pump (for the high side MOSFETs) or from the VGLS internal linear regulator (for the low side MOSFET) to the gate of the MOSFET to charge up the gate. There is a parasitic gate to drain capacitance in a MOSFET that effects how fast a MOSFET can turn on or turn off. This parasitic capacitance must be charged up to turn the MOSFET on. To roughly calculate the turn off and turn on time of a MOSFET, you can use the gate to drain charge of the MOSFET (Qgd found in the MOSFET datasheet), and use the gate drive current (also called IDRIVE or “sink” and “source” current) to calculate the turn on time of the MOSFET. If you use an IDRIVE setting of 90mA source current, and the MOSFET has a Qgd of 18nC, then the turn on time of the MOSFET is Qgd/IDRIVE = 18nC/90mA = 200ns. Most designers consider 200ns turn on time and 100ns turn off time fairly fast for a MOSFET, and it depends on the design of the board how much current the driver can source or sink before there can be significant voltage overshoot/ringing on the gate of the MOSFET during switching events.

Regards,

Anthony