US1150
4A ULTRA LOW DROPOUT POSITIVE
ADJUSTABLE REGULATOR
PRELIMINARY DATASHEET
FEATURES
0.7V Dropout at 4A
Fast Transient Response
1%
Voltage Reference Initial Accuracy
Built-in Thermal Shutdown
DESCRIPTION
The US1150 product is a
4A regulator with extremely
low dropout voltage using a proprietary Bipolar pro-
cess that achieves comparable equivalent on re-
sistance to that of discrete MOSFETs.
This product is
specifically designed to provide well regulated supply for
applications requiring 2.8V or lower voltages from
3.3V ATX power supplies where high efficiency of
a switcher can be achieved without the cost and
complexity associated with switching regulators.
One such application is the new graphic chip sets that
require anywhere from 2.4V to 2.7V supply such as the
Intel I740 chip set.
APPLICATIONS
3.3V to 2.7V Intel I740 chip set.
TYPICAL APPLICATION
3.3V
C1
Vin
Vctrl
5
4
3
R1
US1150
Vout
Adj
Vsense
2.7V
C3
R2
2
1
1150app1-1.0
5V
C2
Typical application of US1150 in a 3.3V to 2.7V for I740 chip.
PACKAGE ORDER INFORMATION
Tj (
°
C)
0 TO 125
5 PIN PLASTIC
5 PIN PLASTIC
TO263 (M)
POWER FLEX (P)
US1150CM
US1150CP
8 PIN PLASTIC
SOIC (S)
US1150CS
Rev. 1.2
10/28/99
2-1
US1150
ABSOLUTE MAXIMUM RATINGS
Input Voltage (Vin) ........................................................... 7V
Control Input Voltage (Vctrl) .................................................. 14V
Power Dissipation............................................. Internally Limited
Storage Temperature Range ................................... -65
°
C TO 150
°
C
Operating Junction Temperature Range ..................... 0
°
C TO 150
°
C
PACKAGE INFORMATION
8 PIN PLASTIC SOIC ( S )
TOP VIEW
5 PIN PLASTIC TO263 ( M )
FRONT VIEW
5
4
3
2
1
5 PIN PLASTIC POWER FLEX (P)
FRONT VIEW
5
4
3
2
1
Vctrl
Vin
Adj
Vsense
1
2
3
4
8
7
6
5
Vout
Vout
Vout
Vout
Vin
Vctrl
Vout
Adj
Vsense
Vin
Vctrl
Vout
Adj
Vsense
θ
JA
=55°C/W for 1" Sq pad area
θ
JA
=35°C/W for 0.5" square pad
θ
JA
=35°C/W for 0.5" square pad
Unless otherwise specified ,these specifications apply over ,Cin=1uF,Cout=10uF, and Tj=0 to 125
°
C.Typical
values refer to Tj=25
°
C. Vout=Vsense.
PARAMETER
Reference Voltage
SYM
Vref
TEST CONDITION
MIN
Vctrl=2.75V,Vin=2V,Io=10mA
1.243
Tj=25,Vadj=0V
Vctrl=2.7to12V,Vin=2.05V to 5.5V, 1.237
Io=10mA to 4A,Vadj=0V
Vctrl=2.5Vto7V,Vin=1.75Vto5.5V
,Io=10mA ,Vadj=0V
Vctrl=2.75V,Vin=2.1V,Io=10mA
to 4A,Vadj=0V
Vadj=0V for all conditions below.
Vin=2.05V,Io=1.5A
Vin=2.05V,Io=3A
Vin=2.05V,Io=4A
Vadj=0V for all conditions below.
Vctrl=2.75V,Io=1.5A
Vctrl=2.75V,Io=3A
Vctrl=2.75V,Io=4A
Vctrl=2.75V,Vin=2.05V,
dVo=100mV Vadj=0V
Vctrl=5V,Vin=3.3V,Vadj=0V,
30 mS Pulse
Vctrl=5V,Vin=5V,Io=4A,Vadj=0V
Tj=25,Vripple=1Vpp at 120Hz
TYP
1.250
1.250
MAX
1.257
1.263
UNITS
V
ELECTRICAL SPECIFICATIONS
Line Regulation
Load Regulation (note 1)
Dropout Voltage (note 2)
(Vctrl - Vout)
3
5
1.15
1.18
1.25
mV
mV
V
1.10
Dropout Voltage (note 2)
(Vin - Vout)
0.26
0.50
0.70
0.38
0.60
0.85
V
Current Limit
Minimum Load Current (note 3)
Thermal Regulation
Ripple Rejection
4.2
5
0.01
70
10
0.02
60
A
mA
%/W
dB
2-2
Rev. 1.2
10/28/99
US1150
ELECTRICAL SPECIFICATIONS
PARAMETER
Control Pin Current
SYM
TEST CONDITION
Vadj=0V for all below conditions.
Vctrl=2.75V,Vin=2.05V,Io=1.5A
Vctrl=2.75V,Vin=2.05V,Io=3A
Vctrl=2.75V,Vin=2.05V,Io=4A
MIN
TYP
6
30
33
50
MAX
10
60
70
120
UNITS
mA
Adjust Pin Current
Iadj
Vctrl=2.75V,Vin=2.05V,Vadj=0V,
uA
Note 1 :
Low duty cycle pulse testing with Kelvin con-
nections are required in order to maintain accurate data.
Note 2 :
Drop-out voltage is defined as the minimum
differential between Vin and Vout required to maintain
regulation at Vout. It is measured when the output volt-
age drops 1% below its nominal value.
Note 3 :
Minimum load current is defined as the mini-
mum current required at the output in order for the out-
put voltage to maintain regulation. Typically the resistor
dividers are selected such that it automatically main-
tains this current.
PIN DESCRIPTIONS
PIN #
1
2
3
4
PIN SYMBOL
Vsense
Adj
Vout
Vctrl
PIN DESCRIPTION
This pin is the positive side of the reference which allows remote load sensing
to achieve excellent load regulation.
A resistor divider from this pin to the Vout pin and ground sets the output voltage.
The output of the regulator. A minimum of 10uF capacitor must be connected from this
pin to ground to insure stability.
This pin is the supply pin for the internal control circuitry as well as the base drive for
the pass transistor.This pin must always be higher than the Vout pin in order for
the device to regulate.(see specifications)
The input pin of the regulator.Typically a large storage capacitor is connected from this
pin to ground to insure that the input voltage does not sag below the minimum drop
out voltage during the load transient response.This pin must always be higher than
Vout in order for the device to regulate.(see specifications)
5
Vin
Rev. 1.2
10/28/99
2-3
US1150
BLOCK DIAGRAM
Vin
Vctrl
Vout
Vsense
1.25V
CURRENT
LIMIT
+
+
THERMAL
SHUTDOWN
Adj
1150blk1-1.1
Figure 1 - Simplified block diagram of the US1150
APPLICATION INFORMATION
Introduction
The US1150 adjustable regulator is a 5 terminal device
designed specificaly to provide extremely low dropout
voltages comparable to the PNP type without the disad-
vantage of the extra power dissipation due to the base
current associated with PNP regulators.This is done by
bringinging out the control pin of the regulator that pro-
vides the base current to the power NPN and connect-
ing it to a voltage that is grater than the voltage present
at the Vin pin.This flexebility makes the US1150 ideal
for applications where dual inputs are available such as
a computer motherboard with an ATX style power sup-
ply that provides 5V and 3.3V to the board.One such
application is the new graphic chip sets that require any-
where from 2.4V to 2.7V supply such as the Intel I740
chip set. The US1150 can easily be programmed with
the addition of two external resistors to any voltages
within the range of 1.25 to 5.5 V. Another major require-
ment of these graphic chips such as the Intel I740 is the
need to switch the load current from zero to several amps
in tens of nanoseconds at the processor pins ,which
translates to an approximately 300 to 500 nS of current
step at the regulator . In addition, the output voltage tol-
erances are also extremely tight and they include the
transient response as part of the specification.
The US1150 is specifically designed to meet the fast
current transient needs as well as providing an accurate
initial voltage , reducing the overall system cost with the
need for fewer number of output capacitors.Another fea-
ture of the device is its true remote sensing capability
which allows accurate voltage setting at the load rather
than at the device.
Output Voltage Setting
The US1150 can be programmed to any voltages in the
range of 1.25V to 5.5V with the addition of R1 and R2
external resistors according to the following formula:
R
2
V
OUT
=
V
REF
1
+ +
I
ADJ
×
R
2
R
1
Wehre : V
REF
=125 V Typically
.
I
ADJ
=50 uA Typically
R
1
& R
2
as shown in figure 2
Vin
Vin
Vout
Vout
US1150
Vctrl
Vctrl
Adj
Vsense
Vref
IAdj = 50uA
R1
R2
1150app2-1.1
Figure 2 - Typical application of the US1150 for
programming the output voltage.
2-4
Rev. 1.2
10/28/99
US1150
The US1150 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 US1150 is 10
mA , R1 is typically selected to be a 121Ω resistor 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 US1150 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 US1150 with remote
sensing.
Vin
Vin
Vout
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.
Thermal Design
The US1150 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.
Pkg
Copper
θ
JA
(°C/W)
Area
1.4"X1.4"
25
1.0"X1.0"
30
0.7"X0.7"
35
Pad Size
45
1.0"X1.0"
55
Max Pd
(
Ta=25°C
)
4.4W
3.7W
3.1W
2.4W
2.0W
Max Pd
(
Ta=45°C
)
3.6W
3.0W
2.6W
2.0W
1.63W
US1150
Vctrl
Vctrl
Adj
Vsense
R1
RL
R2
1150app3-1.0
TO263
TO263
TO263
TO263
SO8
Figure 3 - Schematic showing connection for best
load regulation
Stability
The US1150 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 mΩ and an output
capacitance of 500 to 1000uF. Fortunately as the ca-
pacitance increases, the ESR decreases resulting in a
fixed RC time constant. The US1150 takes advantage of
this phenomena in making the overall regulator loop
stable.
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 low cost applications the SO8 pack-
age is recommended.
Rev. 1.2
10/28/99
2-5
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