US1261 UNISEM, US1261 Datasheet - Page 5

• Manufacturer Part Number: US1261
• Description: DUAL 6A AND 1A LOW DROPOUT POSITIVE FIXED OUTPUT REGULATOR
• Manufacturer: UNISEM

select a heat sink that results in lower temperature rise
than the one calculated in previous step. The following
heat sinks from AAVID and Thermaloy meet this crite-
ria.
Thermalloy
AAVID
Note : For further information regarding the above com-
panies and their latest product offering and application
support contact your local representative or the num-
bers listed below:
Thermalloy
AAVID
Example # 2
Assuming the following specifications :
The steps for selecting a proper heat sink to keep the
junction temperature below 135 C is given as :
1) Calculate the maximum power dissipation using :
2) Assuming a TO-263 surface mount package, the junc-
tion to ambient thermal resistance of the package is:
3) The maximum junction temperature of the device is cal-
culated using the equation below :
Since this is lower than our selected 135 C maximum junc-
tion temperature (150 C is the thermal shutdown of the
device), TO-263 package is a suitable package for our ap-
plication.
Rev. 1.7
3/22/99
I
I
P
P
V
V
V
T
OUT 2
OUT 1
T
T
A
D
D
IN
OUT 2
OUT 1
JA
J
J
I
MAX
35 C
0.2
MAX
3.3V
OUT1
T
35 + 2.86 30 = 121 C
= 2.5 V
30
A
1.5 V
= 0.2 A
:
593101B 551002B 534202B 577102B 576802B
1.5A
7021B
C W for 1"
P
3.3 2.5 + 1.5
D
V
0
PH# [phone]
PH# [phone]
/
IN
JA
V
7020B
100
OUT1
Air Flow (LFM)
square pad area
6021PB
I
OUT2
200
3.3 1.5
V
7173D
IN
300
V
OUT2
2.86 W
7141D
400
Layout Consideration
The US1261 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 con-
nected to this pin using a plane connection with a
low inductance path.
US1261
3-5