IRU1117 Ver la hoja de datos (PDF) - International Rectifier
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IRU1117 Datasheet PDF : 10 Pages
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IRU1117
PIN DESCRIPTIONS
PIN # PIN SYMBOL PIN DESCRIPTION
1
Adj
A resistor divider from this pin to the VOUT pin and ground sets the output voltage.
2
VOUT
The output of the regulator. A minimum of 10mF capacitor must be connected from this pin
to ground to insure stability.
3
VIN
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 dropout
voltage during the load transient response. This pin must always be 1.3V higher than VOUT
in order for the device to regulate properly.
BLOCK DIAGRAM
VIN 3
2 VOUT
+
CURRENT
LIMIT
1.25V +
THERMAL
SHUTDOWN
1 Adj
Figure 2 - Simplified block diagram of the IRU1117.
APPLICATION INFORMATION
Introduction
The IRU1117 adjustable Low Dropout (LDO) regulator is
a three-terminal device which can easily be programmed
with the addition of two external resistors to any volt-
ages within the range of 1.25 to 5.5V. This regulator
only needs 1.3V differential to maintain output regula-
tion. Unlike the first generation of the three-terminal regu-
lators such as LM117 that required 3V differential be-
tween the input and the regulated output.
The IRU1117 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 output capacitors. This is a key require-
ment for today’s low voltage IC applications that typi-
cally need 3.3V supply and are often generated from the
5V supply. Other applications such as high speed
memory termination need to switch the load current from
zero to full load in tens of nanoseconds at their pins,
which translates to an approximately 300 to 500ns cur-
rent step at the regulator. In addition, the output voltage
tolerances are sometimes tight and they include the tran-
sient response as part of the specification.
Rev. 1.8
02/04/03
www.irf.com
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