MIC4609 datasheet(24/34 Pages) MICROCHIP

24 / 34 page

MIC4609

DS20005531A-page 24

 2016 Microchip Technology Inc.

amount of negative voltage on the switch node, a 1A

fast recovery diode and a minimum 10

 resistor are

recommended. A higher current diode and/or larger

values of resistance can be used if necessary.

Adding a series resistor in the switch node limits the

peak high-side driver current, which affects the

switching speed of the high-side driver. The resistor, in

series with the HO pin, may be reduced to help

compensate for the extra HS pin resistance.

FIGURE 5-2:

Negative HS Pin Voltage.

5.3

Power Dissipation Considerations

Power dissipation in the driver can be separated into

two areas:

• Gate driver dissipation

• Quiescent current dissipation used to supply the

internal logic and control functions

5.3.1

GATE DRIVER POWER

DISSIPATION

Power dissipation in the output driver stage is mainly

caused

charging

and

discharging

the

gate-to-emitter and gate-to-collector capacitance of the

external IGBT. Figure 5-3 shows a simplified equivalent

circuit

the

MIC4609

driving

external

high-side IGBT.

FIGURE 5-3:

MIC4609 High-Side Driving

an External IGBT.

5.3.2

DISSIPATION DURING THE

EXTERNAL IGBT/MOSFET

TURN-ON

Energy from capacitor CB is used to charge up the input

capacitance of the IGBT (CGE and CGC). The energy

delivered to the gate is dissipated in the three resistive

components, RON, RG and RG_INT. RG is the series

resistor between the driver output and the IGBT. RG_INT

is the gate resistance of the IGBT. RG_INT is usually

listed in the IGBT or MOSFET specifications. The ESR

of capacitor CB and the resistance of the connecting

etch can be ignored since they are much less than RON

and RG_INT.

The effective capacitances of CGE and CGC are difficult

to calculate because they vary nonlinearly with IC, VGE,

and

VCE. Most power IGBT and MOSFET

specifications include a graph of total gate charge

versus VGE. Figure 5-4 shows a typical gate charge

curve for an arbitrary IGBT. The chart shows that for a

gate voltage of 12V, the IGBT requires 12 nC of charge.

FIGURE 5-4:

Typical Gate Charge vs. VGE.

AHS

AHB

AHO

VDD

ALO

Level

shift

AHI

ALI

COM

VIN

CVDD

RHS

DCLAMP

DBST

VNEG

10W

AHS

AHB

AHO

External

IGBT

VDD

RG_INT

RON

ROFF

CGC

CGE

VIN

RHS

DCLAMP

DBST

048

G, Total Gate Charge (nC)

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