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A8431 Fiches technique(PDF) 4 Page - Allegro MicroSystems

No de pièce A8431
Description  White LED Driver Constant Current Step-up Converter
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Fabricant  ALLEGRO [Allegro MicroSystems]
Site Internet  http://www.allegromicro.com
Logo ALLEGRO - Allegro MicroSystems

A8431 Fiches technique(HTML) 4 Page - Allegro MicroSystems

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26185.301
Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
A8431
White LED Driver Constant Current Step-up Converter
Functional Description
Schematic 1. Typical application
A8431
1
23
5
6
4
VIN
SW
OVP
EN
GND
FB
Li-ion
2.5V to
4.2V
C1
1.0 µF
L1
22 µH
D1
C2
0.22 µF
R1
6.3
Enable
Typical Application
A typical application circuit for the A8431 is provided in
schematic diagram 1. This illustrates a method of driving
three white LEDs in series. The conversion efficiency of this
configuration is shown in chart 1.
Pin Functions
The diagram also shows a method of connecting the individ-
ual pins, whos functions are described as follows:
VIN. Supply to the control circuit.Abypass capacitor, C1, must
be connected from close to this pin to GND.
SW. Low-side switch connection between the inductor, L1,
and ground. Because rapid changes of current occur at this
pin, the traces on the PCB that are connected to this pin should
be minimized. In addition, L1 and the diode D1 should be
connected as close to this pin as possible.
OVP. Overvoltage Protection sense pin to protect the A8431
from excessive voltage on the SW pin. This pin should be
connected to the output capacitor, C2. To disable this feature
connect the pin to ground.
EN. Setting lower than 0.4 V disables the A8431 and puts the
control circuit into the low-power Sleep mode. Greater than
1.5 V fully enables the A8431.
GND. Ground reference connected directly to the ground plane.
Thesenseresistor,R1,shouldhaveaseparateconnectiondirectly
to this point.
FB.FeedbackpinforLEDcurrentcontrol.Thereferencevoltage
is 95 mV. The top of R1 is typically connected here.
60
65
70
75
80
85
90
0
5
10
15
20
LED Current (mA)
VIN = 3 V
VIN = 4 V
Conversion Efficiency versus Current
Chart 1. Conversion efficiency when driving three LEDs
in the typical application circuit.
Preliminary Data Sheet
Subject to Change Without Notice
April 5, 2005


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