AAT3167
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 AAT3167 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 AAT3167 soft-start feature prevents
noise transient effects associated with inrush cur-
rents during start-up of the charge pump circuit.
LED Selection
Although the AAT3167 is designed for driving white
LEDs, the device also can be used to drive most
types of LEDs with forward voltage specifications
ranging from 2.0V to 4.7V. LED applications may
include main and sub-LCD display backlighting,
camera photo-flash applications, color (RGB)
LEDs, infrared diodes for remotes, and other loads
benefiting from a controlled output current generat-
ed from a varying input voltage. Since the D1 to D5
input current sinks are matched with negligible
voltage dependence, the LED brightness will be
matched regardless of the specific LED forward
voltage (VF) levels.
Capacitor Selection
Careful selection of the four external capacitors
(CIN, C1, C2, COUT) is important because they will
affect turn-on time, output ripple, and transient per-
formance. Optimum performance will be obtained
when low equivalent series resistance (ESR)
(<100mΩ) ceramic capacitors are used. 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 lev-
els, 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 AAT3167 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.
3167.2007.03.1.4
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