iru1260 International Rectifier Corp., iru1260 Datasheet - Page 6

• Manufacturer Part Number: iru1260
• Description: Dual 6a And 1a Low Dropout Positive Adjustable Regulator -
• Manufacturer: International Rectifier Corp.

IRU1260
Layout Consideration
The IRU1260 like all other high speed linear regulators
need to be properly laid out to insure stable operation.
The most important component is the output capacitor,
which needs to be placed close to the output pin and
connected to this pin using a plane connection with a
low inductance path.
IRU1260 in Ultra LDO, Single Output Application
The IRU1260 can also be used in single supply applica-
tions where the difference between input and output is
much lower than the standard 1.5V dropout that is ob-
tainable with standard LDO devices. The schematic in
Figure 7 shows the application of the IRU1260 in a single
supply with the second LDO being disabled.
In this application, the IRU1260 is used on the VGA
card to convert 3.3V supply to 2.7V to power the Intel
740 chip rather than the conventional LDO which due to
its 1.5V minimum dropout spec must use the 5V supply
to achieve the same result. The difference is a substan-
tial decrease in the power dissipation as shown below.
6
www.irf.com
The maximum power dissipation of the Intel 740 chip is
5.8W, which at 2.7V results in:
a) Using standard LDO, the power dissipated in the de-
b) Using IRU1260, the power dissipated in the device is
vice is:
Using surface mount TO-263 package with 258C/W
junction to air thermal resistance results in:
This is very close to the thermal shutdown of the IC.
drastically reduced by using 3.3V supply instead of
5V.
Using surface mount TO-263 package with 258C/W
junction to air thermal resistance results in:
A reduction of 918C in junction temperature.
Io =
P
T
P
T
J
J
D
D
= P
= P
= (V
= (V
5.8
2.7
D
D
3u
IN
3u
IN
= 2.15A
- Vo)3Io = (5 - 2.7)32.15 = 4.94W
- Vo)3Io = (3.3 - 2.7)32.15 = 1.3W
JA
JA
+ T
+ T
A
A
= 4.94325 + 25 = 1488C
= 1.3325 + 25 = 578C
09/19/02
Rev. 2.1