 2002 Microchip Technology Inc.

DS21416B-page 7

TC429

Three components make up total package power

dissipation:

The capacitive load-caused dissipation is a direct func-

tion of frequency, capacitive load and supply voltage.

The package power dissipation is:

2

Where:

f

= Switching frequency

C

= Capacitive load

Quiescent power dissipation depends on input signal

duty cycle. A logic low input results in a low-power

dissipation mode with only 0.5mA total current drain.

Logic high signals raise the current to 5mA maximum.

The quiescent power dissipation is:

Where:

(0.5mA max)

D

= Duty cycle

Transition power dissipation arises because the output

stage N- and P-channel MOS transistors are ON

simultaneously for a very short period when the output

changes.

The

transition

package

power

dissipation

is

approximately:

An example shows the relative magnitude for each

item.

C

= 2500pF

D

= 50%

f

= 200kHz

= 113mW + 10mW + 41mW

= 164mW

= 125

°C

Where:

(+150

°C)

(150

°C/W, CERDIP)

Note:

Ambient operating temperature should not

exceed +85

°C for IJA devices or +125°C for

MJA devices.

TABLE 3-1:

MAXIMUM OPERATING

FREQUENCIES

CONDITIONS: 1. CERDIP Package (

FIGURE 3-5:

PEAK OUTPUT

CURRENT CAPABILITY

3.5

POWER-ON OSCILLATION

Note:

It is extremely important that all MOSFET

Driver

applications

be

evaluated

for

the possibility

of

having

High-Power

Oscillations occurring during the power-on

cycle.

Power-on oscillations are due to trace size and layout

as well as component placement. A ‘quick fix’ for most

applications

which

exhibit

power-on

oscillation

problems is to place approximately 10k

Ω in series with

the input of the MOSFET driver.

18V

500kHz

15V

700kHz

10V

1.3MHz

5V

>2MHz

TIME (5

µs/DIV)

5V

INPUT

OUTPUT

5

µs

500mV

5V/DIV

500mV/DIV

(5 AMP/DIV)