To increase the IGBT gate drive current, a non-inverting current buffer (such as the NPN/PNP buffer shown in Figure 9-13) can be used. Inverting types are not compatible with the desaturation fault protection circuitry and must be avoided. The MJD44H11/MJD45H11 pair is appropriate for peak currents up to 15 A, the D44VH10/ D45VH10 pair is up to 20-A peak.

In the case of an over-current detection, the soft turn off (STO) is activated. External components must be added to implement STO instead of normal turn off speed when an external buffer is used. C_STO sets the timing for soft turn off and R_STO limits the inrush current to below the current rating of the internal FET (10A). R_STO must be at least (VDD–VEE)/10. The soft turn off timing is determined by the internal current source of 400 mA and the capacitor C_STO. C_STO is calculated using Equation 11.

Equation 11.

• I_STO is the internal STO current source, 400 mA
• t_STO is the desired STO timing

Figure 9-13 Current Buffer for Increased Drive Strength