AAT3105 Datasheet, PDF (8/15 Pages) Advanced Analogic Technologies – Low Cost 1x/2x 4 Channel Charge Pump WLED Driver

ChargePump^TM
PRODUCT DATASHEET
AAT3105178
Low Cost 1x/2x 4 Channel Charge Pump WLED Driver
Functional Block Diagram
C+ C–
OUT
IN
EN/PWM
Two-Mode
CP Control
V_F Monitoring
PWM Control
4
2x
1x
5
IREF
5 Bits DAC
D1
D2
D3
D4
GND
Functional Description
The AAT3105 is a low-cost charge-pump solution designed
to drive up to four white LEDs. 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 sources
powered from the output of the charge pump. Low 1x
charge-pump output resistance and low dropout voltage
current sources allow the charge pump to stay in 1x mode
with an input voltage as low as 3.8V and LED forward
voltages of 3.5V. After entering 2x mode, the charge
pump remains in 2x mode until the device resets.
The AAT3105 requires only three external components:
one 1μF ceramic capacitor for the charge pump flying
capacitor (C_P), one 1μF ceramic input capacitor (C_IN),
one 1μF ceramic output capacitor (C_OUT). The four con-
stant current outputs of the AAT3105 (D1 to D4) can
drive four individual LEDs with a maximum current of
30mA each. A PWM interface enables the AAT3105 to
change the LED current through the EN/PWM pin.
PWM Interface
The AAT3105 uses a simple PWM interface to control the
effective LED current (RMS) of its current source out-
puts. The PWM signal should fit the requirements listed
in the electrical characteristic table for proper operation.
When the EN/PWM pin is constantly pulled high, which
means 100% duty ratio, the source current per channel
is typically 30mA. When the EN/PWM pin is pulled low
for less than 150μs, the current source will output 0mA
of current and the charge pump status will remain
8
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