MIC44F18_11 Datasheet, PDF (12/17 Pages) Micrel Semiconductor – 6A, 13V High Speed MOSFET Drivers with Enable Input

Micrel, Inc.
MIC44F18/19/20
The power dissipated inside the MIC4100/4101 is equal to
the ratio of R_ON & R_OFF to the external resistive losses in
R_G and R_{G_FET}. Letting R_ON = R_OFF, the power dissipated in
the MIC44F18 due to driving the external MOSFET is:
Pdiss _drive
=
P_DRIVER
R_ON
R_ON
+ R_G + R_{G _ FET}
Supply Current Power Dissipation
Power is dissipated in the MIC44F18 even if is there is
nothing being driven. The supply current is drawn by the
bias for the internal circuitry, the level shifting circuitry and
shoot-through current in the output drivers. The supply
current is proportional to operating frequency and the V_DD
voltage. The typical characteristic graphs show how supply
current varies with switching frequency and supply voltage.
The power dissipated by the MIC44F18 due to supply
current is:
Pdiss_SUPPLY = V_DD × I_DD
Total Power Dissipation and Thermal Considerations
Total power dissipation in the Driver equals the power
dissipation caused by driving the external MOSFETs plus
the supply current:
Figure 6A shows the power dissipation in the driver for
different values of gate charge with V_DD=5V. Figure 6B
shows the power dissipation at V_DD=12V. Figure 6C
show the maximum power dissipation for a given
ambient temperature for the MLF and ePad packages.
The maximum operating frequency of the driver may
be limited by the maximum power dissipation of the
driver package.
Figure 6A. Driver Power Dissipation
Pdiss_TOTAL = Pdiss_SUPPLY + Pdiss_DRIVE
The die temperature may be calculated once the total
power dissipation is known:
T_J = T_A + Pdiss_TOTAL × θ _JA
Where
T_A is the Maximum ambient temperature
T_J is the junction temperature (°C)
Pdiss_TOTAL is the power dissipation of the Driver
θJC is the thermal resistance from junction-to-
ambient air (°C/W)
The following graphs help determine the maximum
gate charge that can be driven with respect to
switching frequency, supply voltage and ambient
temperature.
Figure 6B. Driver Power Dissipation
February 2011
12
M9999-020111