MIC4606 datasheet(24/40 Pages) MICROCHIP

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MIC4606

DS20005604D-page 24

 2017-2019 Microchip Technology Inc.

There are two phases in the MIC4606. The power

dissipation for each of the bootstrap diodes must be

calculated and summed to obtain the total bootstrap

diode power dissipation for the package.

The value of VF should be taken at the peak current

through the diode; however, this current is difficult to cal-

culate because of differences in source impedances.

The peak current can either be measured or the value of

VF at the average current can be used, which will yield a

good approximation of diode power dissipation.

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

typically much less than 1 mW and can be ignored.

An optional external bootstrap diode may be used

instead of the internal diode (Figure 7-6). 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 VDD 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

dissipated in that diode due to reverse leakage can be

calculated as:

EQUATION 7-3:

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.

FIGURE 7-6:

Optional Bootstrap Diode.

7.5

Gate Driver Power Dissipation

Power dissipation in the output driver stage is mainly

caused by charging and discharging the gate to source

and gate to drain capacitance of the external MOSFET.

Figure 7-7 shows a simplified equivalent circuit of the

MIC4606 driving an external high-side MOSFET.

FIGURE 7-7:

MIC4606 Driving an

External High-Side MOSFET.

PDIODErev

IR VREV



–





Where:

IR = Reverse Current Flow at VREV and TJ

VREV = Diode Reverse Voltage

D = Duty Cycle (tON x fS)

xHS

xHB

xHO

xLO

EXTERNAL

DIODE

MIC4606

LEVEL

SHIFT

xHS

xHB

xHO

EXTERNAL

FET

G_FET

OFF

MIC4606

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