a8430 Allegro MicroSystems, Inc., a8430 Datasheet - Page 4

• Manufacturer Part Number: a8430
• Description: White Led Driver Constant Current Step-up Converter
• Manufacturer: Allegro MicroSystems, Inc.

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,
White LED Driver Constant Current Step-up Converter
Li-ion
2.5V to
4.2V
Schematic 1. Typical application
C1
1µF
VIN
Enable
EN
A8430
GND
L1
22µH
FB
SW
D1
R1
6.3Ω
Functional Description
C2
0.22µF
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Worcester, Massachusetts 01615-0036 [phone]
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.
Chart 1. Conversion efficiency when driving various
quantities of LEDs in the typical application circuit
Conversion Efficiency versus Input Voltage
95
90
85
80
75
70
65
2
3
4
5
V
IN
(V)
6
7
3 LEDs
4 LEDs
5 LEDs
8
A8430
9
10
4