iru1176 International Rectifier Corp., iru1176 Datasheet - Page 4

• Manufacturer Part Number: iru1176
• Description: 7.5a Ultra Low Dropout Positive Adjustable Regulator With Shutdown Input
• Manufacturer: International Rectifier Corp.

IRU1176
BLOCK DIAGRAM
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
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
4
V
CTRL
IN
V
SD
pin. This flexibility makes the IRU1176 ideal
IN
6,7
5
2
SHUTDOWN
THERMAL
CURRENT
LIMIT
SHUTDOWN
OUTPUT
Figure 2 - Simplified block diagram of the IRU1176.
+
www.irf.com
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
CTRL
Figure 3 - Typical application of the IRU1176 for
V
Where:
V
I
R
V
ADJ
IN
OUT
REF
1
& R
= 50mA Typically
= 1.25V Typically
= V
2
programming the output voltage.
as shown in Figure 3:
REF
3 o o 1 +
V
V
IN
CTRL
1.25V
Open
SD
IRU1176
R
R
2
1
Adj
p p + I
V
I
+
ADJ
SENSE
V
OUT
= 50uA
ADJ
V
3 R
4
1
3
REF
V
V
Adj
2
R1
R2
OUT
SENSE
03/18/02
Rev. 1.4
V
OUT