Step-Up DC/DC Converters for
White LED Backlight Applications
General Description
The AAT1231/1231-1 are high frequency, high effi-
ciency constant current boost converters capable of
24V maximum output voltage. Both devices are
ideal power solutions for backlight applications with
up to six white LEDs in series or up to twelve white
LEDs in a parallel/series configuration. The input
voltage is 2.7V to 5.5V for single-cell lithium-
ion/polymer (Li-ion) based portable devices.
The LED current is digitally controlled across a 6x
operating range using AnalogicTech’s Simple Serial
Control™ (S
2
Cwire™) interface. Programmability
across 26 discrete current steps provides high reso-
lution, low noise, flicker-free, constant LED outputs.
In programming AAT1231 operation, LED brightness
increases based on the data received at the EN/SET
pin. In programming AAT1231-1 operation, LED
brightness decreases based on the data received at
the EN/SET pin. The SEL logic pin changes the feed-
back voltage between two programmable ranges.
The AAT1231 and the AAT1231-1 feature high current
limit and fast, stable transitions for stepped or pulsed
current applications. The high switching frequency (up
to 2MHz) provides fast response and allows the use
of ultra-small external components, including chip
inductors and capacitors. Fully integrated control cir-
cuitry simplifies design and reduces total solution size.
The AAT1231 and the AAT1231-1 offer a true load
disconnect feature which isolates the load from the
power source while in the OFF or disabled state. This
eliminates leakage current, making the devices ideal-
ly suited for battery-powered applications.
The AAT1231 and the AAT1231-1 are available in Pb-
free, thermally-enhanced 12-pin TSOPJW packages.
AAT1231/1231-1
SwitchReg
™
Features
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Input Voltage Range: 2.7V to 5.5V
Maximum Continuous Output 24V @ 50mA
Drives 6 LEDs in Series, 12 LEDs in Parallel/
Series Configuration
— Constant LED Current with 6% Accuracy
Digital Control with S
2
Cwire Single Wire Interface
— 26 Discrete Steps
— No PWM Control Required
— No Additional Circuitry
Up to 82% Efficiency
Up to 2MHz Switching Frequency Allows
Small External Chip Inductor and Capacitors
Hysteretic Control
— No External Compensation Components
— Excellent Load Transient Response
— High Efficiency at Light Loads
Integrated Soft Start with No External Capacitor
True Load Disconnect Guarantees <1.0µA
Shutdown Current
Selectable Feedback Voltage Ranges for
High Resolution Control of Load Current
Short-Circuit, Over-Voltage, and Over-
Temperature Protection
12-Pin TSOPJW Package
-40°C to +85°C Temperature Range
Applications
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Digital Still Cameras (DSCs)
Mobile Handsets
MP3 Players
PDAs and Notebook PCs
White LED Drivers
Typical Application
L = 2.2µH
DS1
Up to 24V/
50mA max
OSRAM
LW M678
C
2
2.2µF
PVIN
C
1
2.2µF
Li-Ion:
V
IN
= 2.7V to 4.2V
LIN
SW
OVP
R
3
12kΩ
R
2
226kΩ
VIN
PGND
AAT1231/
1231-1
Enable/Set
Select
EN/SET
SEL
FB
AGND
R
1
(R
BALLAST
)
30.1Ω
Capable of Driving
Six LEDs in Series
(see Applications Section)
1231.2007.01.1.2
1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
