iru1150cs International Rectifier Corp., iru1150cs Datasheet - Page 4

• Manufacturer Part Number: iru1150cs
• Description: 4a Ultra Low Dropout Positive Adjustable Regulator -
• Manufacturer: International Rectifier Corp.

IRU1150
BLOCK DIAGRAM
APPLICATION INFORMATION
Introduction
The IRU1150 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 IRU1150 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 such as the Intel I740 is the
need to switch the load current from zero to several amps
in tens of nanoseconds at the processor pins, which
translates to an approximately 300 to 500ns of current
step at the regulator. In addition, the output voltage tol-
erances are also extremely tight and they include the
transient response as part of the specification.
The IRU1150 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
V
IN
IN
pin. This flexibility makes the IRU1150 ideal
5
4
SHUTDOWN
THERMAL
CURRENT
LIMIT
Figure 2 - Simplified block diagram of the IRU1150.
+
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 IRU1150 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:
Where:
V
I
R
ADJ
REF
1
V
CTRL
and R
= 50mA Typically
V
V
= 1.25V Typically
IN
OUT
Figure 3 - Typical application of the IRU1150
2
= V
for programming the output voltage.
as shown in Figure 3:
REF
3 o o 1 +
V
V
IN
CTRL
1.25V
IRU1150
Adj
R
R
2
1
p p + I
I
V
ADJ
SENSE
V
+
OUT
= 50uA
ADJ
V
3 R
REF
3
1
2
2
R2
R1
V
V
Adj
OUT
SENSE
03/18/02
Rev. 1.6
V
OUT