MIC4609 datasheet(25/34 Pages) MICROCHIP

25 / 34 page

 2016 Microchip Technology Inc.

DS20005531A-page 25

MIC4609

The power dissipated by the resistive components of

the gate drive circuit during turn-on is calculated as

shown in Equation 5-3.

EQUATION 5-3:

The power dissipated by each of the internal gate

drivers (high-side or low-side) is equal to the ratio of

RON and ROFF to the external resistive losses in RG

and RG_INT.

Letting RON = ROFF, the power dissipated in the

individual driver output in the IC is calculated as shown

in Equation 5-4:

EQUATION 5-4:

The total power dissipated in the MIC4609, due to

switching, is equal to the sum of all six driver

dissipations.

5.3.3

SUPPLY CURRENT POWER

DISSIPATION

Power is dissipated in the MIC4609 even if nothing is

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 the operating frequency and

the VDD and VHB voltages. Figures 2-9 and 2-10 show

how supply current varies with switching frequency and

supply voltage.

The power dissipated by the MIC4609 due to supply

current is calculated by applying Equation 5-5.

EQUATION 5-5:

5.3.4

TOTAL POWER DISSIPATION AND

THERMAL CONSIDERATIONS

Total power dissipation in the MIC4609 is equal to the

power dissipation caused by driving the external IGBTs

and the supply current. Equation 5-6 shows this

relation.

EQUATION 5-6:

The die temperature can be calculated after the total

power dissipation is determined as shown in

Equation 5-7.

EQUATION 5-7:

Where:

PDRIVER (1) = Average drive circuit power due to

switching

QG = Total gate charge at VGE

VGE = Gate-to-emitter voltage on the

IGBT

fS = Switching frequency of the gate

drive circuit

D (2) = Operating duty cycle of the driver

output

Note 1:

PDRIVER is the power dissipated by the

individual driver for one of the six gate

drive outputs.

Operating duty cycle is the percentage of

time that particular driver output is

switching during one rotation of the

motor.

PDRIVER

QG VGE



PDISS

PDRIVER

RON

RON RG RG_INT

-------------------------------------------------



PDISS_SUPPLY

VDD IDD V



IHB



PDISS_TOTAL

PDISS_SUPPLY

PDISS_DRIVERS



TA PDISS_TOTAL JA



Where:

TA = Maximum ambient temperature (°C)

TJ = Junction temperature (°C)

PDISS_TOTAL = MIC4609 power dissipation (W)

JA = Thermal resistance from

junction-to-ambient air (°C/W)

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