IRU1120CP IRF [International Rectifier], IRU1120CP Datasheet - Page 4

• Manufacturer Part Number: IRU1120CP
• Description: 2A LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR
• Manufacturer: IRF [International Rectifier]

IRU1120
BLOCK DIAGRAM
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
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:
4
IN
V
pin. This flexibility makes the IRU1120 ideal
CTRL
V
SHUTDOWN
IN
THERMAL
CURRENT
LIMIT
2
1
+
Figure 2 - Simplified block diagram of the IRU1120.
www.irf.com
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
overall output voltage. Notice that since the I
cally in the range of 1mA, it only adds a small error to
the output voltage which is negligible.
V
CTRL
V
V
Where:
V
I
R
ADJ
IN
Figure 3 - Typical application of the IRU1120
1.25V
OUT
REF
1
and R
< 1mA Typically
= 1.25V Typically
= V
for programming the output voltage.
REF
2
as shown in Figure 3:
3 1+
+
V
V
( )
IN
CTRL
ADJ
Gnd
IRU1120
R1
R2
current out of the R1 to set the
Adj
+I
I
ADJ
ADJ
V
OUT
3R1
= 1uA
4 V
5 V
3
Gnd
R1
R2
OUT
ADJ
ADJ
08/20/02
Rev. 1.3
is typi-
V
OUT