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IRU1117 Fiches technique(PDF) 5 Page - International Rectifier

No de pièce IRU1117
Description  800mA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR
Download  10 Pages
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Fabricant  IRF [International Rectifier]
Site Internet  http://www.irf.com
Logo IRF - International Rectifier

IRU1117 Fiches technique(HTML) 5 Page - International Rectifier

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IRU1117
5
Rev. 1.8
02/04/03
www.irf.com
To set the output DC voltage, we need to select R1 and
R2:
4) Assuming R1 = 121
V, 1%:
Select R2 = 154
V, 1%
5) Calculate the power dissapation for the schottky di-
ode (D1):
and select a suitable component.
Figure 5 - Final Schematic for half of the
GTL+ termination regulator.
Layout Consideration
The output capacitors must be located as close to the
V OUT
terminal of the device as possible. It is recom-
mended to use a section of a layer of the PC board as a
plane to connect the VOUT pin to the output capacitors to
prevent any high frequency oscillation that may result
due to excessive trace inductance.
VIN = 5V
VF = 0.5V
VOUT = 2.85V
IOUT(MAX) = 0.8A
TA = 35
8C
PD = IOUT
3 (VIN - VF - VOUT)
PD = 0.8
3 (5 - 0.5 - 2.85) = 1.32W
uJA(MAX) =
=
= 75.6
8C/W
TJ - TA
PD
135 - 35
1.32
PD = VF
3 IOUT
PD = 0.5
3 0.8 = 0.4W
Assuming the following specifications:
Where:
VF is the forward voltage drop of the D1 diode as
shown in Figure 5.
+5V is significantly more than required to maintain drop-
out voltage across the IRU1117 when regulating VOUT to
2.85V. The "Extra" voltage means additional power is
dissapated in the IRU1117. The diode dissapates some
of this additional power, allowing the IRU1117 to run cooler.
The steps for selecting the right package with proper
board area for heat sinking to keep the junction tem-
perature below 135
8C is given as:
1) Calculate the maximum power dissipation using:
2) Calculate the maximum
uJA allowed for our ex-
ample:
3) Select a package from the data sheet with lower
uJA
than the one calculated in the previous step.
Selecting TO-252 (D-Pak) with at least 0.5" square
of 0.062" FR4 board using 1oz. copper has 70
°C/W
which is lower than the calculated number.
R2 =
3R1 =
3121 = 154.8V
VOUT
VREF
-1
(
)
2.85
1.25
-1
(
)
IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105
TAC Fax: (310) 252-7903
Visit us at www.irf.com for sales contact information
Data and specifications subject to change without notice. 02/01
2.85V
R1
121
1%
R2
154
1%
5V
C2
22uF
C1
10uF
IRU1117
Adj
VOUT
VIN
D1


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