IRU1175CP IRF [International Rectifier], IRU1175CP Datasheet - Page 4

• Manufacturer Part Number: IRU1175CP
• Description: 7.5A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR
• Manufacturer: IRF [International Rectifier]

IRU1175
BLOCK DIAGRAM
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.
2-82
Vctrl
Vin
SHUTDOWN
THERMAL
CURRENT
LIMIT
Figure 1 - Simplified block diagram of the IRU1175
+
1504
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
1175blk1-1.0
Vctrl
Vin
V
Wehre : V
Where: V
I
R
ADJ
OUT
1
& R
=50 A Typically
programming the output voltage
V
2
REF
as shown in Figure 2
1.25V
REF
Vin
Vctrl
1
=1.25V Typically
= .
125
R
R
IRU1175
+
2
1
V Typically
Adj
I
ADJ
IAdj = 50uA
Vsense
Vout
Vout
Vsense
Adj
R
2
Vref
R1
R2
1175app2-1.0
Vout
11/29/99
Rev. 1.2