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
•
•
•
•
•
•
•
•
•
•
•
•
•
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
•
•
•
•
•
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
Step-Up DC/DC Converters for
White LED Backlight Applications
Pin Descriptions
Pin #
1
2
3
AAT1231/1231-1
Symbol
PVIN
EN/SET
SEL
Function
Input power pin; connected to the source of the P-channel MOSFET. Connect to the
input capacitor(s).
IC enable pin and S
2
Cwire input control to set output current.
FB voltage range select.
For the AAT1231, a logic LOW sets the FB voltage range from 0.1V to 0.4V; a logic
HIGH sets the FB voltage range from 0.3V to 0.6V.
For the AAT1231-1, a logic LOW sets the FB voltage range from 0.4V to 0.1V; a logic
HIGH sets the FB voltage range from 0.6V to 0.3V.
Input voltage for the converter. Connect directly to the PVIN pin.
No connection.
Boost converter switching node. Connect the power inductor between this pin and LIN.
Power ground for the boost converter.
Ground pin.
Feedback pin. Connect a resistor to ground to set the maximum LED current.
Feedback pin for over-voltage protection sense.
Switched power input. Connect the power inductor between this pin and SW.
4
5
6, 7
8
9
10
11
12
VIN
N/C
SW
PGND
AGND
FB
OVP
LIN
Pin Configuration
TSOPJW-12
(Top View)
PVIN
EN/SET
SEL
VIN
N/C
SW
1
2
3
4
5
6
12
11
10
9
8
7
LIN
OVP
FB
AGND
PGND
SW
2
1231.2007.01.1.2
Step-Up DC/DC Converters for
White LED Backlight Applications
Electrical Characteristics
1
T
A
= -40°C to +85°C unless otherwise noted. Typical values are at 25°C, V
IN
= 3.6V.
Symbol
Power Supply
PV
IN
, V
IN
V
OUT(MAX)
I
Q
I
SHDN
I
OUT
ΔV
LINEREG(FB)
/
ΔV
IN
R
DS(ON) L
R
DS(ON) IN
T
SS
V
OVP
I
LIMIT
T
SD
T
HYS
SEL, EN/SET
V
SEL(L)
V
SEL(H)
V
EN/SET(L)
V
EN/SET(H)
T
EN/SET (LO)
T
EN/SET(HI)
T
OFF
T
LAT
I
EN/SET
AAT1231
FB
AAT1231-1
FB
FB Pin Regulation
V
IN
= 2.7V to 5.5V, SEL = GND,
EN/SET = DATA16
V
IN
= 2.7V to 5.5V, SEL = HIGH,
EN/SET = HIGH
0.09
0.564
0.1
0.6
0.11
V
0.636
AAT1231/1231-1
Description
Input Voltage Range
Maximum Output Voltage
Operating Current
Shutdown Current
Maximum Continuous Output
Current
2
Line Regulation
Low Side Switch On Resistance
Input Disconnect Switch
On Resistance
Conditions
Min
2.7
Typ
Max
5.5
24
70
1.0
50
Units
V
V
µA
µA
mA
%/V
mΩ
mΩ
µs
SEL = GND, FB = 0.1V
EN/SET = GND
2.7V < V
IN
< 5.5V, V
OUT
= 24V
V
IN
= 2.7V to 5.5V, V
FB
= 0.6V
40
0.7
80
180
300
1.1
1.2
100
2.5
140
15
1.3
From Enable to Output Regulation;
V
FB
= 300mV
Over-Voltage Protection Threshold V
OUT
Rising
Over-Voltage Hysteresis
V
OUT
Falling
N-Channel Current Limit
T
J
Thermal Shutdown Threshold
T
J
Thermal Shutdown Hysteresis
Soft-Start Time
SEL Threshold Low
SEL Threshold High
Enable Threshold Low
Enable Threshold High
EN/SET Low Time
EN/SET High Time
EN/SET Off Timeout
EN/SET Latch Timeout
EN/SET Input Leakage
V
mV
A
°C
°C
V
V
V
V
µs
µs
µs
µs
µA
0.4
1.4
0.4
V
EN/SET
V
EN/SET
V
EN/SET
V
EN/SET
V
EN/SET
<
>
<
>
=
0.6V
1.4V
0.6V
1.4V
5V V
IN
= 5V
1.4
0.3
75
75
500
500
1
0.1
0.6
0.11
-1
0.09
0.564
FB Pin Regulation
V
IN
= 2.7V to 5.5V, SEL = GND,
EN/SET = HIGH
V
IN
= 2.7V to 5.5V, SEL = HIGH,
EN/SET = DATA16
V
0.636
1. Specification over the -40°C to +85°C operating temperature range is assured by design, characterization, and correlation with statis-
tical process controls.
2. Maximum continuous output current increases with reduced output voltage, but may vary depending on operating efficiency and ther-
mal limitations.
4
1231.2007.01.1.2
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