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A8430 Fiches technique(PDF) 5 Page - Allegro MicroSystems

No de pièce A8430
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

A8430 Fiches technique(HTML) 5 Page - Allegro MicroSystems

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Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
A8430
White LED Driver Constant Current Step-up Converter
Device Operation
The A8430 uses a constant-frequency, current-mode control
scheme to regulate the current through the load. The load
current produces a voltage across the external sense resistor
(R1) and the input at the FB pin. This voltage is then
compared to the internal 95 mV reference to produce an error
signal. The switch current is sensed by the internal sense
resistor and compared to the load current error signal. As the
load current increases, the error signal diminishes, reducing
the maximum switch current and thus the current delivered
to the load. As
the load current decreases, the error signal
rises, increasing the maximum switch current and thus
increasing the current delivered to the load.
To set
the load current, ensure that the required internal
reference value of 95 mV is produced at the desired load. To
do so, select a resistance value for the sense resistor, R1 (Ω),
such that:
R1 = 95 mV/
ILOAD
where
ILOAD is the target load current (mA).
The table below shows typical values for R1. Note that the
resistance value is from the standard E96 series.
As load current is reduced, the energy required in the
inductor diminishes, resulting in the inductor current
dropping to zero for low load current levels. This is known
as Discontinuous mode operation, and results in some low-
frequency ripple. The average load current, however, remains
regulated down to zero.
In Discontinuous mode, when the inductor current drops to
zero, the voltage at the SW pin rings, due to the capacitance
in the resonant LC circuit formed by the inductor and the
capacitance of the switch and the diode. This ringing is
low-frequency and is not harmful. It can be damped with a
resistor across the inductor, but this reduces efficiency and is
not recommended.
Target Load Current
(
ILOAD)
(mA)
Sense Resistor (R1)
(Ω)
5
19.1
10
9.53
12
7.87
15
6.34
20
4.75
0
10
20
30
40
50
60
70
80
90
100
110
120
510
15
20
25
IOUT (mA)
Vin = 3V, 3 LED
Vin = 5V, 3 LED
Vin = 3V, 4 LED
Vin = 5V, 4 LED
Power Dissipation versus IOUT


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Numéro de composants électroniques

No de pièceDescriptionHtml ViewFabricant
A8431 White LED Driver Constant Current Step-up Converter 1  2  3  4  5  More Allegro MicroSystems
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FAN5606 Serial LED Driver with Current-Regulated Step-Up DC/DC Converter 1  2  3  4  5  More Fairchild Semiconductor
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MBI5001 8 BIT CONSTANT CURRENT LED DRIVER 1  2  3  4  5  More List of Unclassifed Manufacturers
MBI5169 8 bit CONSTANT CURRENT LED SINK DRIVER WITH ERROR DETECTION 1  2  3  4  5  More List of Unclassifed Manufacturers
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