mic4123 Micrel Semiconductor, mic4123 Datasheet - Page 9

• Manufacturer Part Number: mic4123
• Description: Mic4123, Mic4124, Mic4125 Low-side Mosfet Driver Bipolar/cmos/dmos Process Final Information
• Manufacturer: Micrel Semiconductor

MIC4123/4124/4125
Total power dissipation, then, is:
Assuming an E-Pad SOIC package, with an θ
this will result in the junction running at:
above ambient, which, given a maximum ambient tempera-
ture of 60°C, will result in a maximum junction temperature
of 89.4°C.
EXAMPLE 2: A MIC4124 operating on a 15V input, with one
driver driving a 50Ω resistive load at 1MHz, with a duty cycle
of 67%, and the other driver quiescent, in a maximum ambi-
ent temperature of 40°C:
First, I
Given R
and:
(because only one side is operating)
and:
(this assumes that the unused side of the driver has its input
grounded, which is more efficient)
then:
M9999-052405
O
must be determined.
0.2454 x 58 = 14.2°C
P
I
I
= (1,000,000 x 15 x 3.3 x 10
= 0.025 W
P
= 0.015W
P
P
O
I
P
P
P
O
O
O
Q
L
Q
D
from the characteristic curves then,
D
T
L
= V
= 15 / (3.3 + 50)
= 0.281A
= I
= 15 x [(0.67 x 0.00125) + (0.33 x 0.000125) +
= V
= 12 x [(0.5 x 0.0035) + (0.5 x 0.0003)]
= 0.0228W
= 0.2160 + 0.0066 + 0.0228
= 0.2454W
= (0.281)
= 0.174W
= F x V
= 0.174 + 0.025 + 0.0150
= 0.213W
2
S
(1 x 0.000125)]
x R
/ (R
S
x [D x I
O
O
x D
S
+ R
x (A•s)/2
2
x 3.3 x 0.67
LOAD
H
+ (1 – D) x I
)
–9
) / 2
L
]
JA
of 58°C/W,
9
In a MLF with an θ
in a junction temperature given the maximum 40°C ambient
of:
The actual junction temperature will be lower than calculated
both because duty cycle is less than 100% and because the
graph lists R
will be somewhat lower.
Definitions
input
R
P
P
V
C
P
P
D = Duty Cycle expressed as the fraction of time the
I
I
I
H
D
D
Q
O
S
L
L
L
T
f = Operating Frequency of the driver in Hertz.
= Load Capacitance in Farads.
= Power supply current drawn by a driver when both
= Power supply current drawn by a driver when both
= Output current from a driver in Amps.
= Total power dissipated in a driver in Watts.
= Power dissipated in the driver due to the driver’s
= Power dissipated in a quiescent driver in Watts.
= Power dissipated in a driver when the output
= Output resistance of a driver in Ohms.
= Power supply voltage to the IC in Volts.
(0.213 x 100) + 40 = 52.8°C
inputs are high and neither output is loaded.
load
changes
states (“shoot-through current”) in Watts.
NOTE: The “shoot-through” current from a dual
transition (once up, once down) for both drivers is
stated in the graph on the following page in ampere-
nanoseconds. This figure must be multiplied by the
number of repetitions per second (frequency to find
Watts).
inputs are low and neither output is loaded.
in Watts.
DS(on)
to the driver is high.
at a T
JA
of 60°C/W, this amount of power results
J
of 125°C and the R
DS(on)
at 52.8°C T
Micrel, Inc.
May 2005
J