US1150
2-1
Rev. 1.2
10/28/99
4A ULTRA LOW DROPOUT POSITIVE
ADJUSTABLE REGULATOR
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.
DESCRIPTION
DESCRIPTION
0.7V Dropout at 4A
Fast Transient Response
1% Voltage Reference Initial Accuracy
Built-in Thermal Shutdown
PRELIMINARY DATASHEET
APPLICATIONS
APPLICATIONS
FEATURES
FEATURES
3.3V to 2.7V Intel I740 chip set.
TYPICAL APPLICATION
TYPICAL APPLICATION
3.3V
US1150
2.7V
C1
C3
1150app1-1.0
5V
C2
R1
R2
1
2
3
4
5
Vsense
Adj
Vout
Vctrl
Vin
Tj (
C) 5 PIN PLASTIC 5 PIN PLASTIC 8 PIN PLASTIC
TO263 (M) POWER FLEX (P) SOIC (S)
0 TO 125 US1150CM US1150CP US1150CS
Typical application of US1150 in a 3.3V to 2.7V for I740 chip.
PACKAGE ORDER INFORMATION
PACKAGE ORDER INFORMATION
US1150
2-2
Rev. 1.2
10/28/99
ABSOLUTE MAXIMUM RATINGS
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
PACKAGE INFORMATION
8 PIN PLASTIC SOIC ( S )
5 PIN PLASTIC TO263 ( M )
5 PIN PLASTIC POWER FLEX (P)
JA
=55
C/W for 1" Sq pad area
JA
=35
C/W for 0.5" square pad
JA
=35
C/W for 0.5" square pad
ELECTRICAL SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
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
SYM
TEST CONDITION
MIN
TYP
MAX
UNITS
Reference Voltage
Vref
Vctrl=2.75V,Vin=2V,Io=10mA
1.243
1.250
1.257
V
Tj=25,Vadj=0V
Vctrl=2.7to12V,Vin=2.05V to 5.5V, 1.237
1.250
1.263
Io=10mA to 4A,Vadj=0V
Line Regulation
Vctrl=2.5Vto7V,Vin=1.75Vto5.5V
,Io=10mA ,Vadj=0V
3
mV
Load Regulation (note 1)
Vctrl=2.75V,Vin=2.1V,Io=10mA
to 4A,Vadj=0V
5
mV
Dropout Voltage (note 2)
Vadj=0V for all conditions below.
(Vctrl - Vout)
Vin=2.05V,Io=1.5A
1.15
V
Vin=2.05V,Io=3A
1.18
Vin=2.05V,Io=4A
1.10
1.25
Dropout Voltage (note 2)
Vadj=0V for all conditions below.
(Vin - Vout)
Vctrl=2.75V,Io=1.5A
0.26
0.38
V
Vctrl=2.75V,Io=3A
0.50
0.60
Vctrl=2.75V,Io=4A
0.70
0.85
Current Limit
Vctrl=2.75V,Vin=2.05V,
dVo=100mV Vadj=0V
4.2
A
Minimum Load Current (note 3)
Vctrl=5V,Vin=3.3V,Vadj=0V,
5
10
mA
Thermal Regulation
30 mS Pulse
0.01
0.02
%/W
Ripple Rejection
Vctrl=5V,Vin=5V,Io=4A,Vadj=0V
60
70
dB
Tj=25,Vripple=1Vpp at 120Hz
FRONT VIEW
1
2
3
4
5
Vsense
Adj
Vout
Vctrl
Vin
4
3
2
1
5
6
7
8
TOP VIEW
Vout
Vsense
Adj
Vin
Vctrl
Vout
Vout
Vout
FRONT VIEW
1
2
3
4
5
Vsense
Adj
Vout
Vctrl
Vin
US1150
2-3
Rev. 1.2
10/28/99
ELECTRICAL SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
PARAMETER
SYM
TEST CONDITION
MIN
TYP
MAX
UNITS
Control Pin Current
Vadj=0V for all below conditions.
Vctrl=2.75V,Vin=2.05V,Io=1.5A
6
10
mA
Vctrl=2.75V,Vin=2.05V,Io=3A
30
60
Vctrl=2.75V,Vin=2.05V,Io=4A
33
70
Adjust Pin Current
Iadj
Vctrl=2.75V,Vin=2.05V,Vadj=0V,
50 120
uA
PIN DESCRIPTIONS
PIN DESCRIPTIONS
PIN # PIN SYMBOL
PIN DESCRIPTION
1 Vsense
This pin is the positive side of the reference which allows remote load sensing
to achieve excellent load regulation.
2
Adj
A resistor divider from this pin to the Vout pin and ground sets the output voltage.
3
Vout
The output of the regulator. A minimum of 10uF capacitor must be connected from this
pin to ground to insure stability.
4
Vctrl
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)
5
Vin
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)
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.
US1150
2-4
Rev. 1.2
10/28/99
APPLICATION INFORMATION
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:
Figure 2 - Typical application of the US1150 for
programming the output voltage.
BLOCK DIAGRAM
BLOCK DIAGRAM
V
V
R
R
I
R
Wehre : V
V Typically
I
lly
R
in figure
OUT
REF
ADJ
REF
ADJ
=
+
+
1
125
2
2
1
2
1
2
= .
=50 uA Typica
& R as shown
Figure 1 - Simplified block diagram of the US1150
Vctrl
Vin
Vsense
1150blk1-1.1
Adj
Vout
THERMAL
SHUTDOWN
CURRENT
LIMIT
1.25V
+
+
Vout
1150app2-1.1
R1
R2
Vin
Vctrl
Vref
IAdj = 50uA
US1150
Vsense
Adj
Vout
Vctrl
Vin
US1150
2-5
Rev. 1.2
10/28/99
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 121
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.
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 m
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.
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
JA
(
C/W) Max Pd Max Pd
Area
(
Ta=25
C
) (
Ta=45
C
)
TO263 1.4"X1.4" 25
4.4W
3.6W
TO263 1.0"X1.0" 30
3.7W
3.0W
TO263 0.7"X0.7" 35
3.1W
2.6W
TO263 Pad Size 45
2.4W
2.0W
SO8
1.0"X1.0" 55
2.0W
1.63W
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.
1150app3-1.0
R1
R2
Vin
Vctrl
RL
US1150
Vsense
Adj
Vout
Vctrl
Vin
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