MIC4607 datasheet(27/42 Pages) MICROCHIP

27 / 42 page

 2016 Microchip Technology Inc.

DS20005610A-page 27

MIC4607

The same energy is dissipated by ROFF, RG, and

RG_FET when the driver IC turns the MOSFET off.

Assuming RON is approximately equal to ROFF, the total

energy and power dissipated by the resistive drive ele-

ments is:

EQUATION 6-7:

and

EQUATION 6-8:

6.6

Supply Current Power Dissipation

Power is dissipated in the input and control sections of

the MIC4607, even if there is no external load. Current

is still drawn from the VDD and HB pins for the internal

circuitry, the level shifting circuitry, and shoot-through

current in the output drivers. The VDD and VHB currents

are proportional to operating frequency and the VDD

and VHB voltages. The Typical Performance Curves

show how supply current varies with switching fre-

quency and supply voltage.

The power dissipated by the MIC4607 due to supply

current is:

EQUATION 6-9:

Values for IDD and IHB are found in the EC table and the

typical characteristics graphs.

6.7

Total Power Dissipation and

Thermal Considerations

Total power dissipation in the MIC4607 is equal to the

power dissipation caused by driving the external MOS-

FETs, the supply currents and the internal bootstrap

diodes.

EQUATION 6-10:

Where:

EDRIVER = Energy dissipated per switching cycle.

PDRIVER = Power dissipated per switching cycle.

QG = Total gate charge at VGS.

VGS = Gate-to-source voltage on the MOSFET.

fS = Switching frequency of the gate drive circuit.

The power dissipated in the driver equals the ratio of

RON and ROFF to the external resistive losses in RG

and RG_FET. Letting RON = ROFF, the power dissipated

in the driver due to driving the external MOSFET is:

EQUATION 6-11:

There are six MOSFETs driven by the MIC4607. The

power dissipation for each of the drivers must be calcu-

lated and summed to obtain the total driver diode power

dissipation for the package.

In some cases, the high-side FET of one phase may be

pulsed at a frequency, fS, while the low-side FET of the

other phase is kept continuously on. Since the MOS-

FET gate is capacitive, there is no driver power if the

FET is not switched. The operation of all driver outputs

must be considered to accurately calculate power dis-

sipation.

The die temperature can be calculated after the total

power dissipation is known.

EQUATION 6-12:

Where:

TA = Maximum ambient temperature.

TJ = Junction temperature (°C).

PdissTOTAL = Total power dissipation of the MIC4607.

ΘJA = Thermal resistance from junction to ambient air.

6.8

Other Timing Considerations

Make sure the input signal pulse width is greater than

the minimum specified pulse width. An input signal that

is less than the minimum pulse width may result in no

output pulse or an output pulse whose width is signifi-

cantly less than the input.

The maximum duty cycle (ratio of high-side on-time to

switching period) is controlled by the minimum pulse

width of the low side and by the time required for the CB

capacitor to charge during the off-time. Adequate time

must be allowed for the CB capacitor to charge up

before the high-side driver is turned on.

6.9

Decoupling and Bootstrap

Capacitor Selection

Decoupling capacitors are required for both the

low-side (VDD) and high-side (xHB) supply pins. These

capacitors supply the charge necessary to drive the

external MOSFETs and also minimize the voltage rip-

ple on these pins. The capacitor from xHB to xHS has

DRIVER



DRIVER



Pdiss

SUPPLY



Pdiss

TOTAL

Pdiss

SUPPLY

Pdiss

DRIVE

DIODE

Pdiss

DRIVER

G_FET

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



Pdiss

TOTAL





MIC4607 데이터시트(PDF) 27 Page - Microchip Technology

MIC4607 데이터시트(HTML) 27 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

데이터시트 다운로드

링크 URL