AAT3169 Datasheet, PDF (11/14 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications

AAT3169
High Efficiency 1X/1.5X/2X Charge
Pump for White LED Applications
AS²Cwire Serial Interface Timing
EN/SET
Address
Address
T_HI
T_LO
T_LAT
1
2
17
18
0
Data
T_LAT
1
2 . . . n ≤ 16
1
Data Reg 1
Data Reg 2
0
n-1
0
Applications Information
LED Selection
Although the AAT3169 is specifically intended for
driving white LEDs, the device can also be used to
drive most types of LEDs with forward voltages
from 2.0V to 4.7V. LED applications may include
main and sub-LCD display backlighting, camera
photo-flash applications, color (RGB) LEDs,
infrared (IR) diodes for remotes, and other loads
benefiting from a controlled output current generat-
ed from a varying input voltage. Since the D1 to D6
input current sinks are matched with negligible volt-
age dependence, the LED brightness will be
matched regardless of the specific LED forward
voltage (V_F) levels.
In some instances (e.g., in high luminous output
applications such as photo flash), it may be neces-
sary to drive high-V_F type LEDs. The low dropout
current sinks in the AAT3169 make it capable of
driving LEDs with forward voltages as high as 4.7V
at full current from an input supply as low as 3.0V.
Outputs can be paralleled to drive high-current
LEDs without complication.
Device Switching Noise Performance
The AAT3169 operates at a fixed frequency of
approximately 1MHz to control noise and limit har-
monics that can interfere with the RF operation of
cellular telephone handsets or other communica-
tion devices. Back-injected noise appearing on the
input pin of the charge pump is 20mV peak-to-
peak, typically ten times less than inductor-based
DC/DC boost converter white LED backlight solu-
tions. The AAT3169 soft-start feature prevents
noise transient effects associated with inrush cur-
rents during start-up of the charge pump circuit.
Capacitor Selection
Careful selection of the four external capacitors
(C_IN, C₁, C₂, and C_OUT) is important because they
will affect turn-on time, output ripple, and transient
performance. Optimum performance will be
obtained when low ESR ceramic capacitors are
used; in general, low ESR may be defined as less
than 100mΩ. A value of 1µF for all four capacitors
is a good starting point when choosing capacitors.
If the LED current sources are only programmed
for light current levels, then the capacitor size may
be decreased.
3169.2006.04.1.0
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