IRU1120
1
Rev. 1.3
08/20/02
www.irf.com
TYPICAL APPLICATION
DESCRIPTION
The IRU1120 is an adjustable linear voltage regulator. It
is packaged in a 5-pin ultra thin-pak surface mount pack-
age. The adjustable output voltage can be set from 1.25V
and up using a simple resistor divider. The input power
can be supplied by a single 5V supply. The regulator is
capable of supplying 2 Amps of continuous current with
an input voltage of 5V. The output is protected by both
current limit and thermal shutdown circuits.
2A LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR
Figure 1 - Typical application of IRU1120.
T
A
(C)
DEVICE PACKAGE OUTPUT
0 To 125 IRU1120CP 5-Pin Ultra Thin-Pak
TM
(P) Adjustable
Data Sheet No. PD94402
PACKAGE ORDER INFORMATION
Stable with ceramic capacitor
Guaranteed < 1.3V Dropout at Full Load Current
Fast Transient Response
2% Voltage Reference Initial Accuracy
Output Current Limiting
Built-In Thermal Shutdown
FEATURES
APPLICATIONS
High Efficiency Linear Regulator
Hard Disk Drivers, CD-ROMs, DVDs
ADSL and Cable Modems
PRELIMINARY DATA SHEET
V
CTRL
V
IN
Gnd
V
OUT
V
ADJ
5V
3.3V
2.5V @ 2A
R1
1K
R2
1K
C3
4.7uF
X5R
IRU1120
1
2
3
4
5
C2
4.7uF
X5R
C1
4.7uF
X5R
IRU1120
2
Rev. 1.3
08/20/02
www.irf.com
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over C
IN
=C
CTRL
=C
OUT
=4.7
m
F. Typical values refer to T
J
=25
8
C
unless otherwise noted. I
FL
=2A. V
ADJ
is connected to V
OUT
and V
IN
=V
CTRL
=5V unless otherwise noted.
u
JA
=30
8
C/W for 1" Square Pad
ABSOLUTE MAXIMUM RATINGS
Input Voltage (V
IN
) .................................................... 10V
Input Voltage (V
CTRL
) ................................................. 10V
Operating Junction Temperature Range ..................... -40C To 150C
Operating Ambient Temperature Range ..................... -40C To 125C
Storage Temperature Range ...................................... -65C To 150C
PACKAGE INFORMATION
5-Pin Ultra Thin-Pak
TM
(P)
PARAMETER
SYM TEST CONDITION
MIN TYP MAX UNITS
V
%Vo
%Vo
%Vo
V
V
V
V
Output Voltage
Line Regulation
Load Regulation
Dropout Voltage
Dropout Voltage
Dropout Voltage
Dropout Voltage
1.275
1.287
0.7
1.25
0.4
0.63
0.9
1.25
1.2
1.25
1.25
0.5
1.13
1.4
0.2
0.3
0.48
0.6
0.75
0.94
1.1
1.27
1.05
1.2
1.225
1.213
Io=10mA, T
J
=25
8
C
Io=10mA, 0
8
C< T
J
<125
8
C
Io=10mA, Vo+1.3V<V
IN
=V
CTRL
<10V
Io=10mA, V
IN
=V
CTRL
=2.6 to 10V for
the following:
0
8
C< T
J
<125
8
C
-40
8
C< T
J
<125
8
C
Note 1, 10mA<Io<2A for the
following:
0
8
C< T
J
<125
8
C
-40
8
C< T
J
<125
8
C
Note 2, Io=1A, V
CTRL
=5V,
V
O
+V
DO1
<V
IN
<3.3V for the following:
0
8
C< T
J
<125
8
C
-40
8
C< T
J
<125
8
C
Note 2, Io=1.5A, V
CTRL
=5V,
V
O
+V
DO2
<V
IN
<3.3V for the following:
0
8
C< T
J
<125
8
C
-40
8
C< T
J
<125
8
C
Note 2, Io=2A, V
CTRL
=5V,
V
O
+V
DO3
<V
IN
<3.3V for the following:
0
8
C< T
J
<125
8
C
-40
8
C< T
J
<125
8
C
Note 2, Io=1A, V
CTRL
=V
IN
for the
following:
0
8
C< T
J
<125
8
C
-40
8
C< T
J
<125
8
C
V
OUT
Reg
LINE
Reg
LOAD
V
DO1
V
DO2
V
DO3
V
DO4
FRONT VIEW
1
2
3
4
5
V
CTRL
V
IN
Gnd
V
OUT
V
ADJ
Tab is
Gnd
IRU1120
3
Rev. 1.3
08/20/02
www.irf.com
PIN # PIN SYMBOL
PIN DESCRIPTION
PIN DESCRIPTIONS
The control input pin of the regulator. This pin is connected to the 5V supply to provide
base current for the pass transistor of the regulator. This allows the regulator to have very
low dropout voltage, enabling use with low values of V
IN
. A 1
m
F high frequency capacitor
is connected from this pin to V
IN
to ensure stability.
The power input pin of the regulator. A minimum of input capacitance must be connected
from this pin to ground to insure that the input voltage does not sag below the minimum
dropout voltage during the load transient response. This pin must always be higher than
the V
OUT
pin by the amount of dropout voltage (see data sheet) in order for the device to
regulate properly.
This pin is connected with ground. It is also the tab of the package.
The output of the regulator. A minimum of output capacitance must be connected from
this pin to ground to insure stability.
A resistor divider from this pin to the V
OUT
pin and to ground sets the output voltage. See
application section for divider setting recommendations and a circuit example.
1
2
3
4
5
V
CTRL
V
IN
Gnd
V
OUT
V
ADJ
Note 1: Low duty cycle pulse testing with Kelvin con-
nections is required in order to maintain accurate data.
Note 2: Dropout voltage is defined as the minimum dif-
ferential voltage between V
IN
and V
OUT
required to main-
tain regulation at V
OUT
. It is measured when the output
voltage 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.
Note 4: Temperature stability is the change in output
from nominal over the operating temperature range.
Note 5: Guaranteed by design, but not tested in produc-
tion.
PARAMETER
SYM TEST CONDITION
MIN TYP MAX UNITS
Dropout Voltage
Dropout Voltage
Current Limit
Minimum Load Current
Thermal Regulation
Ripple Rejection
(Vcc to Output)
Temperature Stability
Long Term Stability
RMS Output Noise
Vcc Quiescent Current
V
V
A
mA
%/W
dB
%Vo
%Vo
%Vo
mA
1.35
1.5
4
5
3
1.2
1.3
1.35
1.44
3
1
0.1
32
0.5
0.3
0.003
1
2.3
Note 2, Io=1.5A, V
CTRL
=V
IN
for the
following:
0
8
C< T
J
<125
8
C
-40
8
C< T
J
<125
8
C
Note 2, Io=2A, V
CTRL
=V
IN
for the
following:
0
8
C< T
J
<125
8
C
-40
8
C< T
J
<125
8
C
D
V
O1
=10% Below Regulation
Note 3, 5
Note 5, 30ms pulse, Io=I
FL
Note 5, 100Hz<f<100KHz, Io=20mA
Note 4, 5, Io=10mA
Note 5
Note 5, 10Hz<f<10KHz
Io=0mA
V
DO5
V
DO6
I
OL
I
O(min)
Reg
THERM
PSRR
Stab
TEMP
Stab
LONG
V
N
I
Q1
IRU1120
4
Rev. 1.3
08/20/02
www.irf.com
APPLICATION INFORMATION
Introduction
The IRU1120 adjustable regulator is a five-terminal de-
vice designed specifically to provide extremely low drop-
out voltages comparable to the PNP type without the
disadvantage of the extra power dissipation due to the
base current associated with PNP regulators. This is
done by bringing out the control pin of the regulator that
provides the base current to the power NPN and con-
necting it to a voltage that is grater than the voltage present
at the V
IN
pin. This flexibility makes the IRU1120 ideal
for applications where dual inputs are available such as
a computer mother board with an ATX style power sup-
ply that provides 5V and 3.3V to the board.
The IRU1120 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.
Output Voltage Setting
The IRU1120 can be programmed to any voltage in the
range of 1.25V to 5.5V by using two external resistors.
The output voltage is defined as:
Where:
V
REF
= 1.25V Typically
I
ADJ
< 1
m
A Typically
R
1
and R
2
as shown in Figure 3:
Figure 3 - Typical application of the IRU1120
for programming the output voltage.
The IRU1120 keeps a constant 1.25V between the ad-
just pin and the ground pin. By replacing a resistor (R2),
between these two pins, a constant current flows through
R1, subtracting the I
ADJ
current out of the R1 to set the
overall output voltage. Notice that since the I
ADJ
is typi-
cally in the range of 1
m
A, it only adds a small error to
the output voltage which is negligible.
Figure 2 - Simplified block diagram of the IRU1120.
BLOCK DIAGRAM
V
CTRL
V
IN
Gnd
2
1
3
4 V
OUT
THERMAL
SHUTDOWN
1.25V
5 V
ADJ
+
+
CURRENT
LIMIT
V
OUT
R1
R2
V
IN
V
CTRL
I
ADJ
= 1uA
IRU1120
Adj
V
OUT
V
CTRL
V
IN
Gnd
V
OUT
= V
REF
3
1+
+I
ADJ
3
R1
R1
R2
(
)
IRU1120
5
Rev. 1.3
08/20/02
www.irf.com
V
OUT
= 2.7V
V
IN
= 3.3V
V
CTRL
= 5V
I
OUT
= 1A (DC Avg)
Assuming, the following conditions:
Calculate the maximum power dissipation using the fol-
lowing equation:
For Ultra Thin-Pak
TM
we have:
Layout Consideration
The IRU1120, like many other high-speed regulators,
requires that the output capacitors be close to the de-
vice for stability. For power consideration, a ground plane
pad of approximately one-inch square on the compo-
nent side must be dedicated to the device where all Gnd
pins are connected to dissipate the power. If a multilayer
board is used, it is recommended that the inner layers of
the board are also dedicated to the size of the pad for
better thermal characteristics.
Thermal Protection
When the junction temperature exceeds 150
8
C, the in-
ternal thermal protection shuts the IRU1120 down.
Current Limit Protection
The IRU1120 provides Over Current Protection when the
output current exceeds typically 3A. The output de-
creases to limit the power dissipation.
Stability
The IRU1120 requires the use of an output capacitor as
part of the frequency compensation in order to make the
regulator stable. A minimum input capacitance of 4.7
m
F
and a minimum output capacitance 4.7
m
F Ceramic ca-
pacitor is needed for regulator stage as well as the speci-
fied minimum loads to guarantee stability.
Transient Response and PSRR
The input and output capacitors are critical in order to
ensure good transient response and PSRR. The most
important aspects of this are capacitor selection, place-
ment and trace routing. Place each capacitor as close
as physically possible to its corresponding regulator pin.
Use wide traces for a low inductance path. Couple di-
rectly to the ground and power planes as possible. The
use of low ESR capacitors is crucial to achieving good
results. Larger capacitance and lower ESR will improve
both PSRR and transient response.
Thermal Design
The IRU1120 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
8
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. The example below shows
the steps in selecting the proper surface mount pack-
age.
P
D
= 1
3
(3.3 - 2.7)+
3
(5 - 2.7) = 0.63W
P
D
= I
OUT
3
(V
IN
- V
OUT
)+
3
(V
CTRL
- V
OUT
)
1
60
(
)
I
OUT
60
(
)
D
T = P
D
3
R
THJA
= 0.63
3
25 = 15.75
8
C
T
J
= T
A
+
D
T = 60.75
8
C
R
THJA
= 25
8
C/W
T
A
= 45
8
C
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