MIC4607 Datasheet, PDF (26/42 Pages) Microchip Technology – 85V, Three-Phase MOSFET Driver with Adaptive Dead-Time, Anti-Shoot-Through and Overcurrent Protection

MIC4607
FIGURE 6-6:
Diode.
Optional External Bootstrap
6.5 Gate Driver Power Dissipation
Power dissipation in the output driver stage is mainly
caused by charging and discharging the gate to source
and gate to drain capacitance of the external MOSFET.
Figure 6-7 shows a simplified equivalent circuit of the
MIC4607 driving an external high-side MOSFET.
MOSFET’s specifications. The ESR of capacitor C_B
and the resistance of the connecting etch can be
ignored since they are much less than R_ON and
R_{G_FET}.
The effective capacitances of C_GD and C_GS are difficult
to calculate because they vary non-linearly with I_D,
V_GS, and V_DS. Fortunately, most power MOSFET spec-
ifications include a typical graph of total gate charge
versus V_GS. Figure 6-8 shows a typical gate charge
curve for an arbitrary power MOSFET. This chart
shows that for a gate voltage of 10V, the MOSFET
requires about 23.5 nC of charge. The energy dissi-
pated by the resistive components of the gate drive cir-
cuit during turn-on is calculated as:
EQUATION 6-4:
Where:
E
=
1--
2

C_ISS

V
2
GS
C_ISS Total gate capacitance of the MOSFET.
but
EQUATION 6-5:
Q = CV
so,
EQUATION 6-6:
E
=
1--
2

Q_G

V
GS
FIGURE 6-7:
MIC4607 Driving an
External High-Side MOSFET.
6.5.1
DISSIPATION DURING THE
EXTERNAL MOSFET TURN-ON
Energy from capacitor C_B is used to charge up the input
capacitance of the MOSFET (C_GD and C_GS). The
energy delivered to the MOSFET is dissipated in the
three resistive components, R_ON, R_G and R_{G_FET}. R_ON
is the on resistance of the upper driver MOSFET in the
MIC4607. R_G is the series resistor (if any) between the
driver and the MOSFET. R_{G_FET} is the gate resistance
of the MOSFET and is typically listed in the power
FIGURE 6-8:
V_GS.
Typical Gate Charge vs.
DS20005610A-page 26
 2016 Microchip Technology Inc.