6A SINGLE HIGH-SPEED,
CMOS POWER MOSFET DRIVER
TC429
Three components make up total package power dissi-
pation:
(1) Capacitive load dissipation (P
C
)
(2) Quiescent power (P
Q
)
(3) 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 dissipa-
tion mode with only 0.5 mA total current drain. Logic high
signals raise the current to 5 mA 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 (5 mA max)
I
L
= Quiescent current with input low (0.5 mA max)
D = Duty cycle.
Transition power dissipation arises because the output
stage N- and P-channel MOS transistors are ON simulta-
neously for a very short period when the output changes.
The transition package power dissipation is approximately:
P
T
= f V
S
(3.3 x 10
–9
A · Sec).
An example shows the relative magnitude for each item.
Example 1:
C = 2500 pF
V
S
= 15V
D = 50%
f = 200 kHz
P
D
= Package power dissipation = P
C
+ P
T
+ P
Q
= 113 mW + 10 mW + 41 mW
= 164 mW.
Maximum operating temperature = T
J
–
θ
JA
(P
D
)
= 125°C,
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.
MAX. POWER (mV)
1
Table 1. Maximum Operating Frequencies
V
S
18V
15V
10V
5V
f
Max
500 kHz
700 kHz
1.3 MHz
>2 MHz
2
3
4
CONDITIONS:
1. CerDIP Package (θ
JA
= 150°C/W)
2. T
A
= +25°C
3. C
L
= 2500 pF
Thermal Derating Curves
1600
1400
1200
8 Pin CerDIP
1000
800
8 Pin SOIC
600
400
200
0
0
10
20
30
40
50
60
70
80
90
100
110
120
8 Pin DIP
AMBIENT TEMPERATURE (°C)
Peak Output Current Capability
5
6
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.
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 prob-
lems is to place approximately 10 kΩ in series with the input
of the MOSFET driver.
4-179
7
8
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
