iru1247-25 International Rectifier Corp., iru1247-25 Datasheet - Page 4

• Manufacturer Part Number: iru1247-25
• Description: Fixed Adjustable Dual Voltage Regulator
• Manufacturer: International Rectifier Corp.

IRU1246 / IRU1247-18 / IRU1247-25
APPLICATION INFORMATION
Thermal
The following thermal design check illustrates the method
used to calculate the maximum junction temperature of
the regulator.
Power Flex Package (Ultra Thin-Pak)
Note 1: This thermal impedance is for a four-layer board
mounted on a minimum of one inch square area. It is
possible to further reduce this by mounting the device
close to other thermally conductive elements such as
mounting screws.
4
R
T
V
I
I
V
V
P
P
T
T
2.5
3.3
A
T = P
J
J
5
2.5
3.3
D
D
THJA
= 98 C
= 45 C
= T
= 5V
= 0.30A
= 0.80A
= (V
= (5 -3.3) × 0.8 + (5-2.5) × 0.3 = 2.11W
= 2.5V
= 3.3V
= 25 C/W (Note 1)
A
D
5
+ ∆T = 45 + 53 = 98 C
-V
× R
3.3
) × I
THJA
3.3
= 2.11 × 25 = 53 C
+ (V
5
-V
2.5
) × I
2.5
Layout Consideration
The IRU1246/1247-xx like many other high speed regu-
lators requires that the output capacitors to be close to
the device for stability reasons. For power consideration,
a ground plane pad of approximately one inch square
pad on the component side must be dedicated to the
device where all ground pins are connected to dissipate
the power. If multilayer board is used, it is recommended
that the inner layers of the board are also dedicated to
the size of the pad for better thermal characteristics.
07/13/01
Rev. 1.6