AAT1235IRN-T1 AnalogicTech, AAT1235IRN-T1 Datasheet - Page 9

• Manufacturer Part Number: AAT1235IRN-T1
• Description: High Efficiency White LED Drivers for Backlight and Keypad
• Manufacturer: AnalogicTech

Functional Block Diagram
SwitchReg
Functional Description
The AAT1235 consists of a controller for the step-up
switching converter and its power switch, and five regu-
lated current sinks each programmable at 16 levels into
two groups, which can be turned on/off individually. An
external Schottky diode, a power inductor, an output
capacitor, and a resistor divider are required to complete
the solution.
The AAT1235’s boost controller is designed to deliver
100mA up to 24V. The AAT1236 is capable of driving a
total of five channels divided into two groups with four
white LEDs connected in series at each channel.
The output load current can be programmed by the cur-
rent sink magnitudes. AS
independent control of two current sink groups (A1 to A3
and B1 to B2) and control on/off with a different con-
figuration on each channel. Unused sink channel(s) must
be connected to AGND to ensure proper function of the
AAT1235.
1235.2009.09.1.2
TM
EN/SET
VIN
OV
IN
2
Cwire programming allows
High Efficiency White LED Drivers for Backlight and Keypad
Converter
AS
Control
Control
Boost
2
Cwire
w w w . a n a l o g i c t e c h . c o m
LIN
GND
V
V
V
V
(A1, A2, A3)
REF
(B1, B2)
REF
AGND
SW
Control Loop
The AAT1235 provides the benefits of current mode con-
trol with a simple hysteretic output current loop provid-
ing exceptional stability and fast response with minimal
design effort. The device maintains exceptional constant
current regulation, transient response, and cycle-by-
cycle current limit without additional compensation com-
ponents.
The AAT1235 modulates the power MOSFET switching
current to maintain the programmed sink current
through each channel. The sink voltage at each channel
is monitored and the controller provides direct feedback
in order to maintain the desired LED current.
The switching cycle initiates when the N-channel MOSFET
is turned ON and current ramps up in the inductor. The
ON interval is terminated when the inductor current
reaches the programmed peak current level. During the
OFF interval, the input current decays until the lower
threshold, or zero inductor current, is reached. The lower
Max Current
Adjustment
ROM
ROM
RSET
D/A
D/A
D/A
D/A
D/A
PRODUCT DATASHEET
AAT1235
A1
A2
A3
B1
B2
9