A8430 Datasheet PDF - Allegro MicroSystems

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A8430
Allegro MicroSystems

Part Number A8430
Description White LED Driver Constant Current Step-up Converter
Page 10 Pages


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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



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A8430
White LED Driver Constant Current Step-up Converter
Functional Block Diagram
FB
SW
VIN VREF
1.25 V
95 mV
A1
EN
Enable
A2
RC
CC
Σ
Ramp
Generator
1.2 MHz
Oscillator
RQ
S
Driver
GND
ELECTRICAL CHARACTERISTICS at TA = 25°C, VIN = 3 V (unless otherwise noted)
Characteristics
Symbol
Test Conditions
Min.
Input Voltage Range
Supply Current
VIN
ISUP
Active: ILOAD = 15 mA,
VLOAD = 12 V
Shutdown (EN = 0 V)
2.5
Feedback Reference Voltage
Feedback Input Current
Switch Current Limit
Switch Frequency
Switch Maximum Duty Cycle
VREF
IFB
ISWLIM
FSW
D
86
0.8
85
Switch Saturation voltage
Switch Leakage Current
Enable Input
VCE(SAT)
ISL
Input Threshold Low
Input Threshold High
Input Leakage
VIL
VIH
Leakage
IIL
1.5
Typ.
2.5
0.1
95
20
300
1.2
90
350
Max.
10
3.5
1
104
75
1.6
5
Units
V
mA
µA
mV
nA
mA
MHz
%
mV
µA
0.4 V
–V
1 µA
Note 1. Measured with 4-layer PCB. Please refer to application note “Package Thermal Characteristics,“ for thermal perfor-
mance measurement for 3 mm x 3 mm MLP package for additional information.
www.allegromicro.com
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
2



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A8430
White LED Driver Constant Current Step-up Converter
Operating Characteristics
Using Typical Application Circuit (Schematic 1)
Quiescent Current versus Input Voltage
2.5
2.0
1.5
1.0
0.5
0
0 2 4 6 8 10
VIN (V)
Quiescent Current versus Temperature
2.15
2.10
2.05
2.00
1.95
1.90
–50
0 50 100
Temperature (°C)
150
Feedback Bias Current versus Temperature
20
15
10
5
0
–50 0
50 100 150
Temperature (°C)
Switching Frequency versus Temperature
1.25
1.20
1.15
1.10
1.05
1.00
–50
0 50 100
Temperature (°C)
150
Switch Pin Voltage versus Temperature
300
250
200
150
100
50
0
–50 0
50 100 150
Temperature (°C)
Conversion Efficiency versus Current
90
85
80
75
70 VIN = 3 V
VIN = 4 V
65
60
0
5 10 15
LED Current (mA)
20
www.allegromicro.com
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
3



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A8430
White LED Driver Constant Current Step-up Converter
Functional Description
Typical Application
A typical application circuit for the A8430 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. A bypass capacitor 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, the inductor (L1) and diode (D1) should
be connected as close to this pin as possible.
EN. Setting lower than 0.4 V disables the A8430 and puts the
control circuit into the low-power Sleep mode. Greater than
1.5 V fully enables the A8430.
GND. Ground reference connected directly to the ground plane.
The sense resistor (R1) should have a separate connection
directly to this point.
FB. Feedback pin for LED current control. The reference
voltage is 95 mV. The top of the sense resistor (R1) is typically
connected to this pin.
L1
22µH
D1
VIN SW
C1
1µF
Li-ion
2.5V to
4.2V
A8430
EN GND FB
Enable
C2
0.22µF
R1
6.3
Schematic 1. Typical application
Conversion Efficiency versus Input Voltage
95
90
85
80
3 LEDs
75 4 LEDs
70 5 LEDs
65
2 3 4 5 6 7 8 9 10
VIN (V)
Chart 1. Conversion efficiency when driving various
quantities of LEDs in the typical application circuit
www.allegromicro.com
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
4



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