IRU1175
2-79
Rev. 1.2
11/29/99
7.5A ULTRA LOW DROPOUT POSITIVE
ADJUSTABLE REGULATOR
The IRU1175 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. This product is specifically designed
to provide well regulated supply for applications requir-
ing very low dropout such as 2.8V from 3.3V ATX power
supplies where the same efficiency as the switcher can
be achieved without the cost and complexity associ-
ated with switching regulators. One such application is
the new graphic chipsets that requires 2.7V supply such
as the Intel I740 chipset.
DESCRIPTION
0.5V Dropout at 7.5A (Equivalent of 67m
)
Fast Transient Response
1%
Voltage Reference Initial Accuracy
Built-in Thermal Shutdown
PRELIMINARY DATASHEET
APPLICATIONS
FEATURES
3.3V to 2.7V Intel I740 chipset
TYPICAL APPLICATION
Typical application of IRU1175
PACKAGE ORDER INFORMATION
Tj (
C) 5-PIN PLASTIC 5-PIN PLASTIC 8-PIN PLASTIC
TO-263 (M) ULTRA THIN-PAK (P) SOIC (S)
0 TO 125 IRU1175CM IRU1175CP IRU1175CS
3.3V
IRU1175
2.7V
C1
C3
1175app1-1.0
5V
C2
R1
R2
1
2
3
4
5
Vsense
Adj
Vout
Vctrl
Vin
100uF
100uF
10uF
100
1%
124
1%
2-80
Rev. 1.2
11/29/99
IRU1175
ABSOLUTE MAXIMUM RATINGS
Input Voltage (Vin) ................................................. 6V
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 )
5-PIN PLASTIC TO-263 ( M ) 5-PIN PLASTIC ULTRA THIN-PAK (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
Unless otherwise specified, these specifications apply over, Cin=1
F, Cout=10
F, and Tj=0 to 125C. Typical
values refer to Tj=25C. 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 7.5A, Vadj=0V
Line Regulation
Vctrl=2.5Vto7V, Vin=1.75Vto5.5V
Io=10mA , Vadj=0V
0.5
3
mV
Load Regulation (note 1)
Vctrl=2.75V, Vin=2.1V, Io=10mA
to 7.5A, Vadj=0V
2
6
mV
Dropout Voltage (note 2)
Vadj=0V for all conditions below.
(Vctrl - Vout)
Vin=2.05V, Io=1.5A
0.95
V
Vin=2.05V, Io=3A
1.00
Vin=2.05V, Io=5A
1.05
Vin=2.05V, Io=7.5A
1.15
1.30
Dropout Voltage (note 2)
Vadj=0V for all conditions below.
(Vin - Vout)
Vctrl=2.75V, Io=1.5A
0.100
0.130 V
Vctrl=2.75V, Io=3A
0.200
0.260
Vctrl=2.75V, Io=5A
0.330
0.430
Vctrl=2.75V, Io=7.5A
0.500
0.650
Current Limit
Vctrl=2.75V, Vin=2.05V,
dVo=100mV Vadj=0V
7.7
9
A
Minimum Load Current (note 3)
Vctrl=5V, Vin=3.3V, Vadj=0V
5
10
mA
Thermal Regulation
30mS Pulse
0.01
0.02
%/W
Ripple Rejection
Vctrl=5V, Vin=5V, Io=3A,Vadj=0V
60
70
dB
Tj=25, Vripple=1Vpp at 120Hz
Vout
Vsense
Adj
Vin
Vctrl
Vout
Vout
Vout
4
3
2
1
5
6
7
8
TOP VIEW
Vsense
Adj
Vout
Vctrl
Vin
FRONT VIEW
1
2
3
4
5
Vsense
Adj
Vout
Vctrl
Vin
FRONT VIEW
1
2
3
4
5
IRU1175
2-81
Rev. 1.2
11/29/99
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
15
mA
Vctrl=2.75V, Vin=2.05V, Io=3A
30
Vctrl=2.75V, Vin=2.05V, Io=5A
50
Vctrl=2.75V, Vin=2.05V, Io=7.5A
75
Adjust Pin Current
Iadj
Vctrl=2.75V, Vin=2.05V, Vadj=0V
50 120
A
PIN DESCRIPTIONS
Note 1: Low duty cycle pulse testing with Kelvin con-
nections are required in order to maintain accurate data.
Note 2: Dropout voltage is defined as the minimum dif-
ferential between Vin and Vout required to maintain regu-
lation at Vout. 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 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 10
F 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)
PIN # PIN SYMBOL
1 Vsense
2
Adj
3
Vout
4
Vctrl
5
Vin
2-82
Rev. 1.2
11/29/99
IRU1175
APPLICATION INFORMATION
Introduction
The IRU1175 adjustable regulator is a five-terminal de-
vice designed specificaly 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 bringinging 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 Vin pin.This flexibility makes the IRU1175 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 chipsets that require any-
where from 2.4V to 2.7V supply such as the Intel I740
chipset. The IRU1175 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 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 IRU1175 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 IRU1175 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 IRU1175 for
programming the output voltage
BLOCK DIAGRAM
V
V
R
R
I
R
Wehre : V
V Typically
OUT
REF
ADJ
=
+
+
1
125
2
1
2
= .
Figure 1 - Simplified block diagram of the IRU1175
Where: V
REF
=1.25V Typically
I
ADJ
=50
A Typically
R
1
& R
2
as shown in Figure 2
1504
Vctrl
Vin
Vsense
1175blk1-1.0
Adj
Vout
THERMAL
SHUTDOWN
CURRENT
LIMIT
1.25V
+
+
Vout
1175app2-1.0
R1
R2
Vin
Vctrl
Vref
IAdj = 50uA
IRU1175
Vsense
Adj
Vout
Vctrl
Vin
IRU1175
2-83
Rev. 1.2
11/29/99
The IRU1175 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 pro-
ducing 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 IRU1175 is
10mA, 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 50
A 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 IRU1175 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 IRU1175 with remote
sensing.
Figure 3 - Schematic showing connection for best
load regulation
Stability
The IRU1175 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 100m
and an output
capacitance of 500 to 1000
F. Fortunately as the ca-
pacitance increases, the ESR decreases resulting in a
fixed RC time constant. The IRU1175 takes advantage
of this phenomena in making the overall regulator loop
stable.
For most applications a minimum of 100
F 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 IRU1175 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
)
TO-263 1.4"X1.4" 25
4.4W
3.6W
TO-263 1.0"X1.0" 30
3.7W
3.0W
TO-263 0.7"X0.7" 35
3.1W
2.6W
TO-263 Pad Size 45
2.4W
2.0W
SO-8
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 SO-8 pack-
age is recommended.
1175app3-1.0
R 1
R 2
Vin
Vctrl
R L
IRU1175
Vsense
A d j
Vout
Vctrl
Vin
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