MIC4607 Datasheet, PDF (25/42 Pages) Microchip Technology – 85V, Three-Phase MOSFET Driver with Adaptive Dead-Time, Anti-Shoot-Through and Overcurrent Protection

mended. If the HS pin voltage exceeds 0.7V, a diode
between the xHS pin and ground is recommended. The
diode reverse voltage rating must be greater than the
high-voltage input supply (V_IN). Larger values of resis-
tance can be used if necessary.
Adding a series resistor in the switch node limits the
peak high-side driver current during turn-off, which
affects the switching speed of the high-side driver. The
resistor in series with the HO pin may be reduced to
help compensate for the extra HS pin resistance.
DBST
VIN
CB
CVDD
VDD
AHB
AHI Level
shift
AHO ^RG
AHS ^RHS
3Ω
DCLAMP
VNEG
Phase
A
ALI
ALO _RG
M
MIC4607
VSS
Phases
B&C
FIGURE 6-5:
Negative HS Pin Voltage.
6.3 Power Dissipation Considerations
Power dissipation in the driver can be separated into
three areas:
• Internal diode dissipation in the bootstrap circuit
• Internal driver dissipation
• Quiescent current dissipation used to supply the
internal logic and control functions.
6.4 Bootstrap Circuit Power
Dissipation
Power dissipation of the internal bootstrap diode pri-
marily comes from the average charging current of the
bootstrap capacitor (C_B) multiplied by the forward volt-
age drop of the diode. Secondary sources of diode
power dissipation are the reverse leakage current and
reverse recovery effects of the diode.
The average current drawn by repeated charging of the
high-side MOSFET is calculated by Equation 6-1.
EQUATION 6-1:
Where:
I _{FAVE} = Q_GATE  f _S
Q_GATE Total gate charge at V_HB – V_HS.
f_S
Gate drive switching frequency.
MIC4607
The average power dissipated by the forward voltage
drop of the diode equals:
EQUATION 6-2:
Where:
Pdiode_FWD = I_{FAVE}  V _F
V_F
Diode forward voltage drop.
There are three phases in the MIC4607. The power dis-
sipation for each of the bootstrap diodes must be calcu-
lated and summed to obtain the total bootstrap diode
power dissipation for the package.
The value of V_F should be taken at the peak current
through the diode; however, this current is difficult to
calculate because of differences in source imped-
ances. The peak current can either be measured or the
value of V_F at the average current can be used, which
will yield a good approximation of diode power dissipa-
tion.
The reverse leakage current of the internal bootstrap
diode is typically 3 μA at a reverse voltage of 85V at
125°C. Power dissipation due to reverse leakage is typ-
ically much less than 1 mW and can be ignored.
An optional external bootstrap diode may be used
instead of the internal diode (Figure 6-6). An external
diode may be useful if high gate charge MOSFETs are
being driven and the power dissipation of the internal
diode is contributing to excessive die temperatures.
The voltage drop of the external diode must be less
than the internal diode for this option to work. The
reverse voltage across the diode will be equal to the
input voltage minus the V_DD supply voltage. The above
equations can be used to calculate power dissipation in
the external diode; however, if the external diode has
significant reverse leakage current, the power dissi-
pated in that diode due to reverse leakage can be cal-
culated with the formula in Equation 6-3:
EQUATION 6-3:
Pdiode_REV = I_R  V _REV  1 – D
Where:
I_R
V_REV
D
Reverse current flow at V_REV and T_J.
Diode reverse voltage.
Duty cycle = t_ON × f_S.
The on-time is the time the high-side switch is conduct-
ing. In most topologies, the diode is reverse biased
during the switching cycle off-time.
 2016 Microchip Technology Inc.
DS20005610A-page 25