Micrel, Inc.

MIC44F18/19/20

February 2011

12

M9999-020111

The power dissipated inside the MIC4100/4101 is equal to

the MIC44F18 due to driving the external MOSFET is:

FET

G

G

ON

ON

DRIVER

drive

R

R

R

R

P

Pdiss

_

+

+

=

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

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:

DD

DD

SUPPLY

I

V

Pdiss

×

=

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:

DRIVE

SUPPLY

TOTAL

Pdiss

Pdiss

Pdiss

+

=

The die temperature may be calculated once the total

power dissipation is known:

JA

TOTAL

A

J

Pdiss

T

T

θ

×

+

=

Where

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 6A shows the power dissipation in the driver for

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

Figure 6B. Driver Power Dissipation