A8430EEK Allegro Microsystems Inc, A8430EEK Datasheet - Page 8

• Manufacturer Part Number: A8430EEK
• Description: IC LED DRVR WHITE BCKLGHT 5-MLPD
• Manufacturer: Allegro Microsystems Inc
• Type: Backlight, White LEDr

Specifications of A8430EEK

• Constant Current: Yes
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 1.2MHz
• Voltage - Supply: 2.5 V ~ 10 V
• Voltage - Output: 36V
• Mounting Type: Surface Mount
• Package / Case: 5-WDFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 20mA
• Internal Switch(s): Yes
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Efficiency: -

By applying a PWM signal directly to the EN pin, the A8430
is turned on or off, and I
R1) or zero. By varying the duty cycle of the PWM signal,
the LED brightness can be controlled from off (0% duty
cycle) to full (100% duty cycle). The PWM frequency should
be in the range from 1 kHz to 10 kHz.
Several other schemes are possible, for example, digitally
switching additional resistors across R1 to increase I
In this case, R1 would be selected for the minimum desired
brightness.
Soft Start-Up
To provide fast start-up operation, no soft start is
implemented in the control circuit. At power-on, the bypass
capacitor (C1) is discharged, which means that the supply
must provide the in-rush current through the inductor.
This can be reduced by modulating the feedback with a soft-
start circuit as shown in schematic 4. When power is first
applied, the capacitor C3 is discharged and pulls the FB pin
high, reducing the output drive to minimum. As C3 charges,
when the bottom drops below about 0.8 V, the feedback from
the sense resistor (R1) takes over full control of the output
current.
Overvoltage Protection
An overvoltage event can occur when the LEDs become
disconnected or fail in an open state. In these cases, the
current flow through the sense resistor becomes zero, thus
the feedback voltage becomes zero. The A8430 compensates
by increasing the on time of the switch, which increases the
output voltage.
White LED Driver Constant Current Step-up Converter
LOAD
is either full (as defined by
LOAD
www.allegromicro.com
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
.
Schematic 4. Soft start operation
Schematic 3. Dimming control with filtered PWM
Li-ion
2.5V to
4.2V
Li-ion
2.5 V to
4.2 V
C1
1µF
C1
1 µF
VIN
Enable
V
C
EN
(PMW)
VIN
A8430
Enable
GND
L1
22µH
EN
R4
10 kΩ
A843
GND
FB
L1
22 µH
SW
FB
D1
C3
100 nF
SW
R3
90 kΩ
C3
2.2 nF
D1
R2
5 kΩ
R2
1kΩ
R3
5kΩ
A8430
R1
6.3 Ω
R1
6.3Ω
C2
0.22 µF
C2
0.22µF
7