PRODUCT DATASHEET
AAT3103
ChargePump
TM
Functional Block Diagram
C+
C–
OUT
3-Channel Charge-Pump LED Driver
IN
Two-Mode
CP Control
3
D1
D2
V
F
Monitoring
D3
AGND
I
REF
EN/SET
(EN/PWM)
S
2
Cwire Control
(PWM Control)
DAC
RSET
Functional Description
The AAT3103 is a low-cost charge-pump solution designed
to drive up to three WLEDs. The charge pump operates
from a 2.7V to 5.5V power source and converts it to volt-
age levels necessary to drive the LEDs. LED current is
individually controlled through integrated current sourc-
es powered from the output of the charge pump. Low 1x
charge-pump output resistance and low-drop voltage
current sources allow the charge pump to stay in 1x
mode with an input voltage as low as 3.75V and LED
forward voltages as high as 3.2V with 20mA LED current.
Once in 2x mode, the charge pump monitors the input
supply voltage and automatically switches back to 1x
mode when there is sufficient input voltage.
The AAT3103 requires only four external components:
one 1μF ceramic capacitor for the charge pump flying
capacitors (C
P
), one 1μF ceramic input capacitor (C
IN
),
one 1μF ceramic output capacitor (C
OUT
) and a resistor
(R
SET
) to set the maximum LED current. The three con-
stant current outputs of the AAT3103 (D1 to D3) can
drive three individual LEDs with a maximum current of
30mA each. AnalogicTech’s S
2
Cwire serial interface
enables the AAT3103-1/-2 and changes the current
source magnitudes through the EN/SET pin. The
AAT3103-4 uses an external PWM signal to enable the IC
and control the brightness of the LEDs.
Constant Current Control Using R
SET
The maximum current is programmed by an external
resistor at the RSET pin. With a 14.3kΩ external resistor
at the RSET pin, the AAT3103 includes an integrated
serial LED current control that sets the full-scale LED
current between 20mA and 0.67mA. The full-scale LED
current can be set higher or lower than 20mA; see Table
4. For maximum accuracy, a 1% tolerance resistor is
recommended.
8
www.analogictech.com
3103.2008.03.1.0
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
