High Efficiency White LED Drivers
for Backlight and Keypad
Functional Block Diagram
LIN
SW
AAT1235
VIN
IN
D/A
A1
OV
Boost
Converter
Control
ROM
D/A
A2
D/A
V
(A1, A2, A3)
V
REF
V
(B1, B2)
V
REF
ROM
D/A
A3
D/A
B1
B2
EN/SET
AS
2
Cwire
Control
Max Current
Adjustment
GND
AGND
RSET
Functional Description
The AAT1235 consists of a controller for the step-up
switching converter and its power switch, and five
regulated 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
current sink magnitudes. AS
2
Cwire programming
allows independent control of two current sink
groups (A1 to A3 and B1 to B2) and control on/off
with a different configuration on each channel.
Unused sink channel(s) must be connected to
AGND to ensure proper function of the AAT1235.
Control Loop
The AAT1235 provides the benefits of current
mode control with a simple hysteretic output cur-
rent loop providing 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 components.
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 pro-
vides direct feedback in order to maintain the
desired LED current.
1235.2007.02.1.1
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ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
