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What is US1260CT?

This electronic component, produced by the manufacturer "UNISEM", performs the same function as "DUAL 6A AND 1A LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR".


US1260CT Datasheet PDF - UNISEM

Part Number US1260CT
Description DUAL 6A AND 1A LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR
Manufacturers UNISEM 
Logo UNISEM Logo 


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US1260
DUAL 6A AND 1A LOW DROPOUT
POSITIVE ADJUSTABLE REGULATOR
FEATURES
Guaranteed <1.3V Dropout at 6A (output #2)
Guaranteed <0.6V Dropout at 1A (output #1)
Fast Transient Response
1% Voltage Reference Initial Accuracy
Built in Thermal Shutdown
APPLICATIONS
Providing a single package solution for GTL+
and High Speed Bus Termination
Dual supply P55Capplications
DESCRIPTION
The US1260 product using a proprietary process com-
bines a dual low drop out adjustable output regulators in
a single package with one output having a minimum of
6A and the other one having a 1A output current capabil-
ity. This product is specifically designed to provide well
regulated supplies for low voltage ICs such as 3.3V to
1.5V and 2.5V supplies for the GTL+ termination
and the new clock for Pentium II applications.Other
applications include low cost dual supply for proces-
sors such as Intel P55Cwhere 2.8V and 3.3 V are
needed for the Core and the I/O supplies from the
5V input.
TYPICAL APPLICATION
1260app7-1.0
3.3V
C1
U1
US1260
Vout1 7
Vin 6
Vout2 5
Gnd 4
Vfb2 3
Vfb1 2
Vctrl 1
5V
C4
R5
C5
R1
R2
R3
R4
2.5V / 1A
C2
1.5V / 6A
C3
Typical application of US1260 in the Pentium ΙΙ™ design with the 1.5V output providing for GTL+ termination
while 2.5V supplies the clock chip.
Notes: Pentium ΙΙ is trade mark of Intel Corp.
Notes: P55C is trade mark of Intel Corp.
PACKAGE ORDER INFORMATION
Tj (°C)
0 TO 150
7 PIN PLASTIC
TO220(T)
US1260CT
7 PIN PLASTIC
TO263(M)
US1260CM
7 PIN PLASTIC
POWER FLEX(P)
US1260CP
Rev. 1.9
3/22/99
3-1

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US1260CT equivalent
US1260
Stability
The US1260 requires the use of an output capacitor as
part of the frequency compensation in order to make the
regulator stable. Typical designs for the microproces-
sor applications use standard electrolytic capacitors with
typical ESR in the range of 50 to 100 mand the output
capacitance of 500 to 1000uF. Fortunately as the ca-
pacitance increases, the ESR decreases resulting in a
fixed RC time constant. The US1260 takes advantage of
this phenomena in making the overall regulator loop
stable. For most applications a minimum of 100uF alu-
minum electrolytic capacitor with the maximum ESR of
0.3such as Sanyo, MVGX series ,Panasonic FA se-
ries as well as the Nichicon PL series insures both sta-
bility and good transient response. The US1260 also
requires a 1 uF ceramic capacitor connected from Vin
to Vctrl and a 10, 0.1W resistor in series with Vctrl pin
in order to further insure stability.
Thermal Design
The US1260 incorporates an internal thermal shutdown
that protects the device when the junction temperature
exceeds the maximum allowable junction temperature.
Although this device can operate with junction tempera-
tures in the range of 150°C ,it is recommended that the
selected heat sink be chosen such that during maxi-
mum continuous load operation the junction tempera-
ture is kept below this number. Two examples are given
which shows the steps in selecting the proper regulator
heat sink for driving the Pentium II processor GTL+ ter-
mination resistors and the Clock IC using 1260 in TO220
or TO-263 packages.
Example # 1
Assuming the following specifications :
VIN = 3.3V
VOUT 2 = 1.5 V
VOUT 1 = 2.5 V
IOUT 2 MAX = 5.4A
IOUT 1 MAX = 0.4 A
TA = 35° C
2) Select a package from the datasheet and record its
junction to case (or Tab) thermal resistance.
Selecting TO220 package gives us :
θJC =2.7°C/W
3) Assuming that the heat sink is Black Anodized, cal-
culate the maximum Heat sink temperature allowed :
Assume , θSA = 0.05 °C/W (Heat sink to Case thermal
resistance for Black Anodized)
( )TS = TJ PD × θJC + θCS
TS = 135 10 × (2.7 + 0.05) = 107.4 ° C
4) With the maximum heat sink temperature calculated
in the previous step, the Heat Sink to Air thermal resis-
tance θSA is calculated as follows :
T = TS TA = 107.4 35 = 72.4 ° C
θSA = T
PD
θSA = 72.4 = 7.24 ° C / W
10
5) Next , a heat sink with lower θSA than the one calcu-
lated in step 4 must be selected. One way to do this is
to simply look at the graphs of the “Heat Sink Temp
Rise Above the Ambient” vs. the “Power Dissipation” and
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
Air Flow (LFM)
0 100 200 300 400
7021B 7020B 6021PB 7173D 7141D
593101B 551002B 534202B 577102B 576802B
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
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 = 0.4 × (3.3 2.5) + 5.4 × (3.3 1.5) = 10 W
Rev. 1.9
3/22/99
3-5


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US1260CTThe function is DUAL 6A AND 1A LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR. UNISEMUNISEM

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