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What is US1176CM?

This electronic component, produced by the manufacturer "UNISEM", performs the same function as "7.5A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR WITH SHUTDOWN INPUT".


US1176CM Datasheet PDF - UNISEM

Part Number US1176CM
Description 7.5A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR WITH SHUTDOWN INPUT
Manufacturers UNISEM 
Logo UNISEM Logo 


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US1176
7.5A ULTRA LOW DROPOUT POSITIVE
ADJUSTABLE REGULATOR WITH SHUTDOWN INPUT
FEATURES
PRELIMINARY DATASHEET
DESCRIPTION
Guaranteed <TBDV Dropout at 7.5A
Fast Transient Response
1% Voltage Reference Initial Accuracy
Built-in Thermal Shutdown
APPLICATIONS
3.3V to 2.7V Intel I740 chip set.
The US1176 product is a 7.5A regulator with extremely
low dropout voltage using a proprietary Bipolar pro-
cess that achieves comparable equivalent on re-
sistance to that of discrete MOSFETs. The US1176
also provides a convenient Shutdown pin that allows the
regulator to be shutdown and reduce the input current
consumption. Unlike the PNP type regulators this de-
vice does not have high quiecent current during the start
up mode making it ideal for applications where there is
limited current capability such operation from the 5V
Standby supply of the computer power supply.One ap-
plication is the new generation of the RDRAM memory
that needs to provide 2.5V from 3.3V input and be able
to operate from 5VSB as well.
TYPICAL APPLICATION
3.3V
C1
US1176
Vin 7
Vin 6
Vctrl 5
Vout 4
Adj 3
SD 2
Vsense 1
1176app1-1.1
5V
C2
Q1
2.7V
R1
C3
R2
SD Enable
Typical application of US1176 .
PACKAGE ORDER INFORMATION
Tj (°C)
0 TO 125
7 PIN PLASTIC
TO263 (M)
US1176CM
7 PIN PLASTIC
POWER FLEX (P)
US1176CP
Rev. 1.1
9/24/99
2-1

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US1176CM equivalent
US1176
The US1176 keeps a constant 1.25V between the Vsense
pin and the Vadj pin. By placing a resistor R1 across
these two pins and connecting the Vsense and Vout pin
together , a constant current flows through R1, adding
to the Iadj current and into the R2 resistor producing a
voltage equal to the (1.25/R1)*R2 + Iadj*R2 .This voltage
is then added to the 1.25V to set the output voltage.
This is summarized in the above equation. Since the
minimum load current requirement of the US1176 is 10
mA , R1 is typically selected to be a 121resistor so
that it automatically satisfies this condition. Notice that
since the Iadj is typically in the range of 50uA it only
adds a small error to the output voltage and should be
considered when very precise output voltage setting is
required.
Load Regulation
Since the US1176 has separate pins for the output (Vout)
and the sense (Vsense), it is ideal for providing true re-
mote sensing of the output voltage at the load.This
means that the voltage drops due to parasitic resistance
such as PCB traces between the regulator and the load
are compensated for using remote sensing. Figure 3
shows a typical application of the US1176 with remote
sensing.
Vin
Vctrl
Vin Vout
US1176
Vctrl
Vsense
Adj
R1
R2
RL
For most applications a minimum of 100uF aluminum
electrolytic capacitor such as Sanyo, MVGX series
,Panasonic FA series as well as the Nichicon PL series
insures both stability and good transient response.
Shutdown Operation
The US1176 can be disabled by pulling the S.D pin low
using an open collector device such as a low cost 2N3904
general purpose transistor as shown in the application
circuit. The current sink of the pin is equal to:
Isink=(Vctrl-1.4)/R where, R=50 ktyp.
Thermal Design
The US1176 incorporates an internal thermal shutdown
that protects the device when the junction temperature
exceeds the allowable maximum 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 continuos load operation the junction temperature
is kept below this number. The example below shows
the steps in selecting the proper surface mount pack-
age.
Assuming, the following conditions:
Vout=2.7V
Vin=3.3V
Vctrl=5V
Iout=2A DC Avg
Calculate the maximum power dissipation using the fol-
lowing equation:
Pd=Iout*(Vin-Vout) + (Iout/60)*(Vctrl - Vout)
Pd=2*(3.3-2.7) + (2/60)*(5-2.7)=1.28 W
Using table below select the proper package and the
amount of copper board needed.
1176app3-1.0
Figure 3 - Schematic showing connection for best
load regulation
Stability
The US1176 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 an output
capacitance of 500 to 1000uF. Fortunately as the ca-
pacitance increases, the ESR decreases resulting in a
fixed RC time constant. The US1176 takes advantage of
this phenomena in making the overall regulator loop
stable.
Pkg Copper θJA(°C/W)
Area
M or P 1.4"X1.4" 25
M or P 1.0"X1.0" 30
M or P 0.7"X0.7" 35
M or P Pad Size 45
Max Pd
(Ta=25°C)
4.4W
3.7W
3.1W
2.4W
Max Pd
(Ta=45°C)
3.6W
3.0W
2.6W
2.0W
Note: Above table is based on the maximum junction
temperature of 135°C.
As shown in the above table, any of the two packages
will do the job. For lower cost applications the Power
Flex package is recommended.
Rev. 1.1
9/24/99
2-5


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Featured Datasheets

Part NumberDescriptionMFRS
US1176CMThe function is 7.5A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR WITH SHUTDOWN INPUT. UNISEMUNISEM
US1176CPThe function is 7.5A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR WITH SHUTDOWN INPUT. UNISEMUNISEM

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