TC429
Three components make up total package power
dissipation:
• Capacitive load dissipation (P
C
)
• Quiescent power (P
Q
)
• Transition power (P
T
)
The capacitive load-caused dissipation is a direct func-
tion of frequency, capacitive load and supply voltage.
The package power dissipation is:
P
C
= f C V
S2
Where:
f
= Switching frequency
C = Capacitive load
V
S
= Supply voltage
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:
P
Q
= V
S
(D (I
H
) + (1 – D) I
L
)
Where:
I
H
= Quiescent current with input high (5mA max)
I
L
= Quiescent current with input low
(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
approximately:
package
power
dissipation
is
V
S
= 18V
R
L
= 0.1Ω
5V
500mV
Where:
T
J
= Maximum allowable junction temperature
(+150°C)
θ
JA
= Junction-to-ambient thermal resistance
(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:
V
S
18V
15V
10V
5V
MAXIMUM OPERATING
FREQUENCIES
f
MAX
500kHz
700kHz
1.3MHz
>2MHz
CONDITIONS:
1. CERDIP Package (
θ
JA
=150
°
C/W)
2. T
A
= +25
°
C
3. C
L
= 2500pF
FIGURE 3-5:
PEAK OUTPUT
CURRENT CAPABILITY
5V/DIV
500mV/DIV
(5 AMP/DIV)
INPUT
OUTPUT
P
T
= f V
S
(3.3 x 10
–9
A • Sec)
An example shows the relative magnitude for each
item.
C
V
S
D
f
P
D
= 2500pF
= 15V
= 50%
= 200kHz
= Package power dissipation = P
C
+ P
T
+ P
Q
= 113mW + 10mW + 41mW
= 164mW
5µs
TIME (5µs/DIV)
3.5
Note:
POWER-ON OSCILLATION
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.
Maximum operating temperature = T
J
–
θ
JA
(P
D
)
= 125°C
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 10kΩ in series with
the input of the MOSFET driver.
2002 Microchip Technology Inc.
DS21416B-page 7
MICROCHIP [ MICROCHIP TECHNOLOGY ]
