Data Sheet No. PD94132
IRU1176
7.5A ULTRA LOW DROPOUT POSITIVE
ADJUSTABLE REGULATOR WITH SHUTDOWN INPUT
DESCRIPTION
The IRU1176 is a 7.5A regulator with extremely low drop-
out voltage using a proprietary Bipolar process that
achieves comparable equivalent on resistance to that of
discrete MOSFETs. The IRU1176 also provides a conve-
nient shutdown pin that allows the regulator to be shut-
down and reduce the input current consumption. Unlike
the PNP type regulators this device does not have high
quiescent current during the start up mode making it
ideal for applications where there is limited current ca-
pability such operation from the 5V standby supply of
the computer power supply. One application is the new
generation of RDRAM memory that needs to provide 2.5V
from 3.3V input and be able to operate from 5VSB as
well.
FEATURES
Guaranteed <0.65V 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
TYPICAL APPLICATION
3.3V
C1
V
IN
V
IN
V
CTRL
7
6
5
4
3
2
1
R2
R1
C3
IRU1176
V
OUT
Adj
SD
V
SENSE
2.7V
5V
C2
Q1
SD
Enable
Figure 1 - Typical application of IRU1176.
PACKAGE ORDER INFORMATION
T
J
(°C)
0 To 125
7-PIN PLASTIC
TO-263 (M)
IRU1176CM
7-PIN PLASTIC
Ultra Thin-Pak
TM
(P)
IRU1176CP
Rev. 1.5
07/16/02
www.irf.com
1
IRU1176
ABSOLUTE MAXIMUM RATINGS
Input Voltage (V
IN
) ....................................................
Control Input Voltage (V
CTRL
) .....................................
Power Dissipation .....................................................
Storage Temperature Range ......................................
Operating Junction Temperature Range .....................
7V
14V
Internally Limited
-65°C To 150°C
0°C To 150°C
PACKAGE INFORMATION
7-PIN PLASTIC TO-263 (M)
FRONT VIEW
7
7-PIN PLASTIC ULTRA THIN-PAK
T M
(P)
FRONT VIEW
Tab is
V
OUT
6
5
4
3
2
1
V
IN
V
IN
V
CTRL
V
OUT
Adj
SD
V
SENSE
Tab is
V
OUT
7
6
5
4
3
2
1
V
IN
V
IN
V
CTRL
V
OUT
Adj
SD
V
SENSE
θ
JA
=35°C/W for 0.5" square pad
θ
JA
=35°C/W for 0.5" square pad
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over C
IN
=1mF, C
OUT
=10mF and T
J
=0 to 1258C.
Typical values refer to T
J
=258C. V
OUT
=V
SENSE
.
PARAMETER
Reference Voltage
SYM
V
REF
TEST CONDITION
V
CTRL
=2.75V, V
IN
=2V, Io=10mA,
T
J
=258C, V
ADJ
=0V
V
CTRL
=2.7 to 12V, V
IN
=2.05V to 5.5V,
MIN
1.225
1.225
TYP
1.250
1.250
0.5
5
0.95
1.00
1.05
1.15
0.075
0.150
0.200
0.375
MAX
1.275
1.275
UNITS
V
Io=10mA to 7.5A, V
ADJ
=0V
Line Regulation
Load Regulation (Note 1)
Dropout Voltage (Note 2)
(V
CTRL
- V
OUT
)
V
CTRL
=2.5V to 7V, V
IN
=1.75V to 5.5V,
Dropout Voltage (Note 2)
(V
IN
- V
OUT
)
Current Limit
Minimum Load Current (Note 3)
Thermal Regulation
Ripple Rejection
SD Threshold Voltage
SD Input Current
Io=10mA , V
ADJ
=0V
V
CTRL
=2.75V, V
IN
=2.1V,
Io=10mA to 7.5A, V
ADJ
=0V
V
ADJ
=0V for all conditions below:
V
IN
=2.05V, Io=1.5A
V
IN
=2.05V, Io=3A
V
IN
=2.05V, Io=4A
V
IN
=2.05V, Io=7.5A
V
ADJ
=0V for all conditions below:
V
CTRL
=2.75V, Io=1.5A
V
CTRL
=2.75V, Io=3A
V
CTRL
=2.75V, Io=4A
V
CTRL
=2.75V, Io=7.5A
V
CTRL
=2.75V, V
IN
=2.05V,
DVo=100mV,
V
ADJ
=0V
V
CTRL
=5V, V
IN
=3.3V, V
ADJ
=0V
30ms Pulse
V
CTRL
=5V, V
IN
=5V, Io=4A, V
ADJ
=0V,
T
J
=258C, V
RIPPLE
=1V
PP
at 120Hz
V
CTRL
=5V, SD=0V
www.irf.com
mV
mV
V
V
7.7
9
5
0.01
70
10
0.02
A
mA
%/W
dB
V
mA
Rev. 1.5
07/16/02
60
V
CTRL
-1.4 V
CTRL
-2.2
94
130
2
IRU1176
PARAMETER
Control Pin Current
SYM
TEST CONDITION
V
ADJ
=0V for all below conditions:
V
CTRL
=2.75V, V
IN
=2.05V, Io=1.5A
V
CTRL
=2.75V, V
IN
=2.05V, Io=3A
V
CTRL
=2.75V, V
IN
=2.05V, Io=4A
V
CTRL
=2.75V, V
IN
=2.05V, Io=7.5A
V
CTRL
=2.75V, V
IN
=2.05V, V
ADJ
=0V
MIN
TYP
MAX
UNITS
mA
Adjust Pin Current
I
ADJ
50
120
mA
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 between V
IN
and V
OUT
required to maintain regu-
lation 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. Typically the resistor
dividers are selected such that it automatically main-
tains this current.
PIN DESCRIPTIONS
PIN #
1
PIN SYMBOL
V
SENSE
PIN DESCRIPTIONS
This pin is the positive side of the reference which allows remote load sensing to achieve
excellent load regulation.
When this pin is pulled lower than 1.4V with respect to the V
CTRL
pin the device is shut-
down. To enable the operation leave this pin open. Internal to device, there is a pull-up
resistor.
A resistor divider from this pin to the V
OUT
pin and ground sets the output voltage.
The output of the regulator. A minimum of 10mF 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 V
OUT
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 V
OUT
in
order for the device to regulate. (See specifications)
2
SD
3
4
Adj
V
OUT
5
V
CTRL
6, 7
V
IN
Rev. 1.5
07/16/02
www.irf.com
3
IRU1176
BLOCK DIAGRAM
V
IN
6,7
V
CTRL
5
4 V
OUT
1 V
SENSE
1.25V
CURRENT
LIMIT
+
+
THERMAL
SHUTDOWN
3 Adj
SD 2
OUTPUT
SHUTDOWN
Figure 2 - Simplified block diagram of the IRU1176.
APPLICATION INFORMATION
Introduction
The IRU1176 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 IRU1176 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. 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 IRU1176 can easily be programmed with
the addition of two external resistors to any voltages
within the range of 1.25 to 5.5V. Another major require-
ment of these graphic chips is the need to switch the
load current from zero to several amps in tens of nano-
seconds at the processor pins, which translates to an
approximately 300 to 500ns of current step at the regu-
lator. In addition, the output voltage tolerances are also
extremely tight and they include the transient response
as part of the specification.
The IRU1176 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 IRU1176 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:
V
OUT
= V
REF
3
1+
(
R2
R1
)
+I
ADJ
3R2
Where:
V
REF
= 1.25V Typically
I
ADJ
= 50mA Typically
R
1
& R
2
as shown in Figure 3:
V
IN
V
OUT
V
IN
V
OUT
IRU1176
V
CTRL
V
CTRL
SD
V
SENSE
Adj
V
REF
R1
Open
I
ADJ
= 50uA
R2
Figure 3 - Typical application of the IRU1176 for
programming the output voltage.
4
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Rev. 1.5
07/16/02
IRU1176
The IRU1176 keeps a constant 1.25V between the V
SENSE
pin and the V
ADJ
pin. By placing a resistor R1 across
these two pins and connecting the V
SENSE
and V
OUT
pin
together, a constant current flows through R1, adding to
the I
ADJ
current and into the R2 resistor producing a volt-
age equal to the (1.25/R1)3R2 + I
ADJ
3R2.
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 IRU1176 is
10mA, R1 is typically selected to be a 121V resistor so
that it automatically satisfies this condition. Notice that
since the Iadj is typically in the range of 50mA it adds a
small error to the output voltage and should be consid-
ered when very precise output voltage setting is required.
Load Regulation
Since the IRU1176 has separate pins for the output (V
OUT
)
and the sense (V
SENSE
), 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 4
shows a typical application of the IRU1176 with remote
sensing.
V
I N
V
IN
V
OUT
Panasonic FA series as well as the Nichicon PL series
insures both stability and good transient response.
Shutdown Operation
The IRU1176 can be disabled by pulling the SD 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:
I
SINK
=
(V
CTRL
- 1.4)
R
Where: R=50KV Typically
Thermal Design
The IRU1176 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 continuous load operation the junction tempera-
ture is kept below this number. The example below
shows the steps in selecting the proper surface mount
package.
Assuming, the following conditions:
V
OUT
= 2.7V
V
IN
= 3.3V
V
CTRL
= 5V
I
OUT
= 2A (DC Avg)
IRU1176
V
C T R L
V
CTRL
Adj
R1
V
SENSE
R
L
Calculate the maximum power dissipation using the fol-
lowing equation:
P
D
= I
OUT
3(V
IN
- V
OUT
)+
R2
P
D
Figure 4 - Schematic showing connection
for best load regulation.
Stability
The IRU1176 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 100mV and an output
capacitance of 500 to 1000mF. Fortunately as the ca-
pacitance increases, the ESR decreases resulting in a
fixed RC time constant. The IRU1176 takes advantage
of this phenomena in making the overall regulator loop
stable.
For most applications a minimum of 100mF aluminum
electrolytic capacitor such as Sanyo, MVGX series,
(
I60
)
3(V
- V )
2
= 23(3.3 - 2.7)+
( )
3(5
- 2.7) = 1.28W
60
OUT
CTRL
OUT
Using table below select the proper package and the
amount of copper board needed.
Pkg
M
M
M
M
or
or
or
or
P
P
P
P
Copper
θ
JA
(°C/W)
Area
1.4"x1.4"
25
1.0"x1.0"
30
0.7"x0.7"
35
Pad Size
45
Max Pd
(
T
A
=25°C
)
4.4W
3.7W
3.1W
2.4W
Max Pd
(
T
A
=45°C
)
3.6W
3.0W
2.6W
2.0W
Note:
Above table is based on the maximum junction
temperature of 1358C.
As shown in the above table, any of the two packages
will do the job. For lower cost applications the Ultra Thin-
Pak is recommended.
Rev. 1.5
07/16/02
www.irf.com
5
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