IRU1011-33CH Ver la hoja de datos (PDF) - International Rectifier
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IRU1011-33CH Datasheet PDF : 6 Pages
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IRU1011-33(PbF)
APPLICATION INFORMATION
Introduction
The IRU1011-33 regulator is a 3-terminal device offered
in a fixed output of 3.3V and it is designed specifically to
provide an extremely low dropout voltage.
The IRU1011-33 is 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.
Thermal Protection
When the junction temperature exceeds 150 C, the in-
ternal thermal protection shuts the IRU1011-33 down.
Current Limit Protection
The IRU1011-33 provides Over Current Protection when
the output current exceeds typically 2A. The output de-
creases to limit the power dissipation.
Stability
The IRU1011-33 requires the use of an output capacitor
as part of the frequency compensation in order to make
the regulator stable. A minimum input capacitance of
4.7µF and a minimum output capacitance 4.7µF Ce-
ramic capacitor is needed for regulator stage as well as
the specified minimum loads to guarantee stability.
Transient Response and PSRR
The input and output capacitors are critical in order to
ensure good transient response and PSRR. The most
important aspects of this are capacitor selection, place-
ment and trace routing. Place each capacitor as close
as physically possible to its corresponding regulator pin.
Use wide traces for a low inductance path. Couple di-
rectly to the ground and power planes as possible. The
use of low ESR capacitors is crucial to achieving good
results. Larger capacitance and lower ESR will improve
both PSRR and transient response.
Thermal Design
The IRU1011-33 incorporates an internal thermal shut-
down that protects the device when the junction tem-
perature exceeds the allowable maximum junction tem-
perature. Although this device can operate with junction
temperatures in the range of 150 C, it is recommended
that the selected heat sink be chosen such that during
maximum continuous load operation the junction tem-
perature is kept below this number. The example below
shows the steps in selecting the proper surface mount
package.
Assuming, the following conditions:
VOUT = 3.3V
VIN = 5V
IOUT = 1A (DC Avg)
Calculate the maximum power dissipation using the fol-
lowing equation:
PD = IOUT × (VIN - VOUT)
PD = 1 × (5 - 3.3) = 1.7W
For MLPM package, we have:
RTHJA = 32 C/W
TA = 45 C
∆T = PD×RTHJA = 1.7×32 = 54.4
TJ = TA+∆T = 99.4 C
Layout Consideration
The IRU1011-33, like many other high-speed regulators,
requires that the output capacitors be close to the de-
vice for stability. For power consideration, a ground plane
pad of approximately one-inch square on the compo-
nent side must be dedicated to the device where all Gnd
pins are connected to dissipate the power. If a multilayer
board is used, it is recommended that the inner layers of
the board are also dedicated to the size of the pad for
better thermal characteristics.
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