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PDF A8430 Data sheet ( Hoja de datos )
| Número de pieza | A8430 | |
| Descripción | White LED Driver Constant Current Step-up Converter | |
| Fabricantes | Allegro MicroSystems | |
| Logotipo |  |
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A8430
White LED Driver Constant Current Step-up Converter
A8430 MLPD
Approximate actual size
SW
GND
FB
1
2
3
5 VIN
4 EN
Same pad footprint as SOT-23-5
RθJA = 50 °C/W, see note 1, page 2
ABSOLUTE MAXIMUM RATINGS
The A8430 is a noninverting boost converter that steps-up the input
voltage, to provide a programmable constant current output at up to
36 V for driving white LEDs in series. Driving LEDs in series ensures
identical currents and uniform brightness. Up to four white LEDs can
be driven at 20 mA from a single cell Li-ion or a multicell NiMH power
source. Up to seven white LEDs can be driven by increasing the supply
voltage up to 10 V.
The A8430 incorporates a power switch and feedback sense amplifier
to provide a solution with minimum external components. The output
current can be set by adjusting a single external sense resistor and can
be varied with a voltage or filtered PWM signal when dimming control
is required. The high switching frequency of 1.2 MHz allows the use of
small inductor and capacitor values.
The A8430 is provided in a 5-pin 3 mm x 3 mm MLP package (part
number suffix EK), that has a nominal height of only 0.75 mm. The
lead-free version (part number suffix EK-T) has 100% lead-free matte
tin leadframe plating.
FEATURES
Output voltage up to 36 V
2.5 V to 10 V input
Drives up to 4 LEDs at 20 mA from a 2.5 V supply
Drives up to 5 LEDs at 20 mA from a 3 V supply
1.2 MHz switching frequency
300 mA switch current limit
1 µA shutdown current
SW Pin ................................................–0.3 V to 36 V
Remaining Pins .................................. –0.3 V to 10 V
Ambient Operating Temperature, TA....... –40°C to 85°C
Junction Temperature, TJ(max)............................... 150°C
Storage Temperature, TS .................... –55°C to 150°C
APPLICATIONS
LED backlights
Portable battery-powered equipment
Cellular phones
PDAs (Personal Digital Assistant)
Camcorders, personal stereos, MP3 players, cameras
Mobile GPS systems
Use the following complete part number when ordering:
Part Number
Package
Description
A8430EEK
5-pin, MLPD
Surface Mount
A8430EEK-T
5-pin, MLPD
Lead-Free, Surface Mount
1 page  
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:
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.
R1 = 95 mV/ ILOAD
where ILOAD is the target load current (mA).
120
110
100
90
80
70
60
50
40
30
20
10
0
5
Power Dissipation versus IOUT
10
Vin = 3V, 3 LED
15
IOUT (mA)
20
Vin = 5V, 3 LED
Vin = 3V, 4 LED
25
Vin = 5V, 4 LED
Target Load Current
(ILOAD)
(mA)
5
10
12
15
20
Sense Resistor (R1)
(Ω)
19.1
9.53
7.87
6.34
4.75
www.allegromicro.com
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
5
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet A8430.PDF ] | |
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