MIC4607 Datasheet, PDF (27/42 Pages) Microchip Technology – 85V, Three-Phase MOSFET Driver with Adaptive Dead-Time, Anti-Shoot-Through and Overcurrent Protection

The same energy is dissipated by R_OFF, R_G, and
R_{G_FET} when the driver IC turns the MOSFET off.
Assuming R_ON is approximately equal to R_OFF, the total
energy and power dissipated by the resistive drive ele-
ments is:
EQUATION 6-7:
E_DRIVER = Q_G  V _GS
and
EQUATION 6-8:
P_DRIVER = Q_G  V _GS  f _S
6.6 Supply Current Power Dissipation
Power is dissipated in the input and control sections of
the MIC4607, even if there is no external load. Current
is still drawn from the V_DD and HB pins for the internal
circuitry, the level shifting circuitry, and shoot-through
current in the output drivers. The V_DD and V_HB currents
are proportional to operating frequency and the V_DD
and V_HB voltages. The Typical Performance Curves
show how supply current varies with switching fre-
quency and supply voltage.
The power dissipated by the MIC4607 due to supply
current is:
EQUATION 6-9:
Pdiss_SUPPLY = V _DD  I _DD + V _HB  I _HB
Values for I_DD and I_HB are found in the EC table and the
typical characteristics graphs.
6.7 Total Power Dissipation and
Thermal Considerations
Total power dissipation in the MIC4607 is equal to the
power dissipation caused by driving the external MOS-
FETs, the supply currents and the internal bootstrap
diodes.
EQUATION 6-10:
Pdiss_TOTAL = Pdiss_SUPPLY + Pdiss_DRIVE + P_DIODE
Where:
E_DRIVER = Energy dissipated per switching cycle.
P_DRIVER = Power dissipated per switching cycle.
Q_G = Total gate charge at V_GS.
V_GS = Gate-to-source voltage on the MOSFET.
f_S = Switching frequency of the gate drive circuit.
MIC4607
The power dissipated in the driver equals the ratio of
R_ON and R_OFF to the external resistive losses in R_G
and R_{G_FET}. Letting R_ON = R_OFF, the power dissipated
in the driver due to driving the external MOSFET is:
EQUATION 6-11:
Pdiss_DRIVER
=
P_DRIVER

--------------------^R----^O----^N---------------------
R_ON + R_G + R_{G_FET}
There are six MOSFETs driven by the MIC4607. The
power dissipation for each of the drivers must be calcu-
lated and summed to obtain the total driver diode power
dissipation for the package.
In some cases, the high-side FET of one phase may be
pulsed at a frequency, f_S, while the low-side FET of the
other phase is kept continuously on. Since the MOS-
FET gate is capacitive, there is no driver power if the
FET is not switched. The operation of all driver outputs
must be considered to accurately calculate power dis-
sipation.
The die temperature can be calculated after the total
power dissipation is known.
EQUATION 6-12:
T _J = T _A + Pdiss_TOTAL  _JA
Where:
T_A = Maximum ambient temperature.
T_J = Junction temperature (°C).
P_dissTOTAL = Total power dissipation of the MIC4607.
Θ_JA = Thermal resistance from junction to ambient air.
6.8 Other Timing Considerations
Make sure the input signal pulse width is greater than
the minimum specified pulse width. An input signal that
is less than the minimum pulse width may result in no
output pulse or an output pulse whose width is signifi-
cantly less than the input.
The maximum duty cycle (ratio of high-side on-time to
switching period) is controlled by the minimum pulse
width of the low side and by the time required for the C_B
capacitor to charge during the off-time. Adequate time
must be allowed for the C_B capacitor to charge up
before the high-side driver is turned on.
6.9 Decoupling and Bootstrap
Capacitor Selection
Decoupling capacitors are required for both the
low-side (V_DD) and high-side (xHB) supply pins. These
capacitors supply the charge necessary to drive the
external MOSFETs and also minimize the voltage rip-
ple on these pins. The capacitor from xHB to xHS has
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DS20005610A-page 27