How Switching Losses Vary with the Parasitic Capacitances

How Switching Losses Vary with the Parasitic Capacitances 

The gray vertical dashed line (annotated 35 nC ) represents the Si4442DY as it is. So under the stated conditions, we have an estimated switching loss of 2.6 W. If we increase Ciss by 50%, that is, 4200 pF to 6300 pF, we see that Qg will go up to about 47 nC, and the loss to 2.8 W only. 

In other words, Qg will certainly affect driver dissipation, but it is not necessarily a good indicator of the switching losses — it is more helpful to try and minimize Qgd (or Crss) when selecting mosfets, rather than just looking for a low-Qg mosfet. 

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