AAT3169
High Efficiency 1X/1.5X/2X Charge
Pump for White LED Applications
AS2Cwire Serial Interface Timing
Address
Data
THI
TLAT
TLO
TLAT
EN/SET
Address
1
2
17
18
1
2 . . .
n <= 16
0
1
0
0
n
Data Reg 1
Data Reg 2
Device Switching Noise Performance
Applications Information
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.
LED Selection
Although the AAT3169 is designed for driving white
LEDs, the device also can 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 generated from a vary-
ing input voltage. Since the D1 to D6 input current
sinks are matched with negligible voltage depend-
ence, the LED brightness will be matched regard-
less of the specific LED forward voltage (VF) levels.
Capacitor Selection
Careful selection of the four external capacitors
(CIN, C1, C2, and COUT) 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 programmed only
for light current levels, then the capacitor size may
be decreased.
In some instances (e.g., in high luminous output
applications such as photo flash), it may be neces-
sary to drive high-VF 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.
3169.2006.08.1.2
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
