IRU1237SC IRF [International Rectifier], IRU1237SC Datasheet - Page 5

• Manufacturer Part Number: IRU1237SC
• Description: THREE INTEGRATED, FIXED OUTPUT LINEAR VOLTAGE REGULATORS
• Manufacturer: IRF [International Rectifier]

APPLICATION INFORMATION
Introduction
The IRU1237SC regulator is 7-pin terminal device and
contains three integrated, fixed, linear regulators. The
dual inputs provide a low dropout voltage for V
by biasing the base current to power NPN transistors.
The IRU1237SC is designed to meet the fast current
transient needs as well as an accurate initial voltage,
thus reducing the overall system cost with the need for
fewer number of output capacitors.
Thermal Protection
The IRU1237SC provides thermal protection for all three
outputs. All outputs will be disabled for any over-tem-
perature condition. When one of the outputs exceeds
the thermal limit (typically 1508C), the IRU1237SC shuts
down all three outputs simultaneously. The outputs will
be re-enabled when the temperature drops below the
thermal limit.
Current Limit Protection
The IRU1237SC provides over current protection when
one the outputs’ current exceeds the current limit level.
Stability
The IRU1237SC doesn’t require input and output capaci-
tors for stability, however to improve the transient re-
sponse and guarantee stability, it is recommended that
a 0.1mF (minimum) ceramic for input and output capaci-
tors be used.
Transient Response and PSRR
The input and output capacitors are critical in order to
ensure good transient response and PSSR. The most
important aspects of this are capacitor selection, place-
ment, and trace routing. Place each capacitor as close
as physically possible to it’s corresponding regulator pin.
Use wide traces for low inductance path. Couple directly
to the ground and power planes as possible. The use of
low ESR capacitors is crucial to achieving good results.
An input capacitance of at least 0.1mF is recommended.
An output capacitance of at least 0.1mF with low ESR is
recommended for good PSSR at high frequencies. Ce-
ramic capacitors are a good choice for low ESR. Larger
capacitance and lower ESR will improve both PSSR and
transient response.
Rev. 1.2
07/14/03
33
and V
www.irf.com
26
Thermal Design
The IRU1237SC incorporates an internal thermal shut-
down that protects the device when the junction tem-
perature exceeds the allowable maximum junction tem-
perature. Although this device can operate with junction
temperatures in the range of 1508C, it is recommended
that the selected heat sink be chosen such that during
maximum continuous load operation the junction tem-
perature is kept below this number.
The following thermal design illustrates the method used
to calculate the maximum junction temperature of the
regulator.
Calculating the maximum power dissipation:
For Ultra Thin-Pak
Layout Consideration
The IRU1237SC, like many other high-speed regulators,
requires that the output capacitors be close to the de-
vice for stability. For power consideration, a ground plane
pad of approximately one-inch square on the compo-
nent side must be dedicated to device where all ground
pins are connected to dissipate the power. The copper
area under the package shall have vias to the internal
ground plane. The thermal ground plane shall extend out
from the regulator to open areas of the PCB. All open
areas shall be filled with copper to help radiate heat from
the PCB.
V
V
P
V
P
P
R
T
DT = P
T
OUT3
A
J
D
D
IN1
IN2
D
TH(JA)
= T
= 508C
= (5.25-2.6)30.5+(5.25-3.3)30.5+(12-8)30.1
= 2.7W
= (V
=5.25V
=12V
)3I
A
=30W/8C
+DT = 1318C
D
IN1
3R
OUT3
-V
TH(JA)
O U T 1
TM
V
V
V
OUT1
OUT2
OUT3
)3 I
we have:
= 2.7W330 = 818C
=2.6V
=3.3V
=8V
OUT1
+(V
IN1
IRU1237SC
-V
I
I
I
OUT1
OUT2
OUT3
OUT2
=0.5A
=0.5A
=0.1A
)3 I
OUT2
+(V
IN2
5
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