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PDF US1261 Data sheet ( Hoja de datos )

Número de pieza US1261
Descripción DUAL 6A AND 1A LOW DROPOUT POSITIVE FIXED OUTPUT REGULATOR
Fabricantes UNISEM 
Logotipo UNISEM Logotipo



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US1261
DUAL 6A AND 1A LOW DROPOUT
POSITIVE FIXED OUTPUT REGULATOR
FEATURES
Guaranteed to provide 1.5V and 2.5V Sup-
plies with 3.1V input.
Fast Transient Response
1% Voltage Reference Initial Accuracy
Built in Thermal Shutdown
APPLICATIONS
Pentium II Processor Applications
DESCRIPTION
The US1261 product using a proprietary process com-
bines a dual low dropout regulators with fixed outputs of
1.5V and 2.5V in a single package with the 1.5V out-
put having a minimum of 6A and the 2.5V having a 1A
output current capability. This product is specifically de-
signed to provide well regulated supplies from 3.3V to
generate 1.5V for GTL+ termination resistor supply
and 2.5V clock supply for the new generation of
the Pentium II processor applications.
TYPICAL APPLICATION
1261app1-1.3
3.3V
C1
Vout1 5
US1261
Vin 4
Gnd 3
Vout2 2
Vctrl 1
5V
R1
C2
2.5V / 1A
C3
1.5V / 6A
C4
Typical application of US1261 in a Pentium II processor application
PACKAGE ORDER INFORMATION
Tj (°C)
0 TO 150
5 PIN PLASTIC
TO220(T)
US1261CT
5 PIN PLASTIC
TO263(M)
US1261CM
5 PIN PLASTIC
POWER FLEX(P)
US1261CP
Rev. 1.7
3/22/99
3-1

1 page




US1261 pdf
US1261
select a heat sink that results in lower temperature rise Layout Consideration
than the one calculated in previous step. The following
heat sinks from AAVID and Thermaloy meet this crite- The US1261 like all other high speed linear regulators need
ria. to be properly laid out to insure stable operation. The most
Air Flow (LFM)
important component is the output capacitor, which
Thermalloy
AAVID
0 100 200 300 400 needs to be placed close to the output pin and con-
7021B 7020B 6021PB 7173D 7141D nected to this pin using a plane connection with a
593101B 551002B 534202B 577102B 576802B low inductance path.
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
PH# (214) 243-4321
PH# (603) 528-3400
Example # 2 :
Assuming the following specifications :
VIN = 3.3V
VOUT 2 = 1.5 V
VOUT 1 = 2.5 V
IOUT 2 MAX = 1.5A
IOUT 1 MAX = 0.2 A
TA = 35° C
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 :
( ) ( )PD = IOUT1 × VIN VOUT1 + IOUT2 × VIN VOUT2
PD = 0.2 × (3.3 2.5) + 1.5 × (3.3 1.5) = 2.86 W
2) Assuming a TO-263 surface mount package, the junc-
tion to ambient thermal resistance of the package is:
θJA = 30° C / W for 1" square pad area
3) The maximum junction temperature of the device is cal-
culated using the equation below :
TJ = TA + PD × θJA
TJ = 35 + 2.86 × 30 = 121 ° C
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
3-5

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