AAT3152
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
S
2
Cwire Serial Interface Timing
T
HI
T
LO
T
LAT
T
OFF
EN/SET
1
2
n
n <= 16
Data Reg
1
n
0
Auto-Disable Feature
The AAT3152 is equipped with an "auto-disable"
feature for each LED channel. After the IC is
enabled and started up, a test current of 150µA
(typical) is forced through each sink channel. The
channel will be disabled if the voltage of that par-
ticular current sink pin does not drop to a certain
threshold. This feature is very convenient for dis-
abling an unused channel (by tying the DX pin to
V
OUT
) or during an LED fail short event.
Thermal Protection
The AAT3152 has a built-in thermal protection cir-
cuit that will shut down the charge pump if the die
temperature rises above the thermal limit, as is the
case during a short circuit of the V
OUT
pin.
current generated from a varying input voltage.
Since the D1 to D4 input current sinks are matched
with negligible voltage dependence, the LED
brightness will be matched regardless of the spe-
cific LED forward voltage (V
F
) levels. In some
instances (e.g., in high-luminous-output applica-
tions such as photo-flash), it may be necessary to
drive high-V
F
type LEDs. The
low-dropout
current
sinks in the AAT3152 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 AAT3152 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 AAT3152 soft-start feature prevents
noise transient effects associated with in-rush cur-
rents during start up of the charge pump circuit.
Applications Information
LED Selection
Although the AAT3152 is specifically intended for
driving white LEDs, the device can also 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 dis-
play backlighting, camera photo-flash applications,
color (RGB) LEDs, infrared (IR) diodes for remotes,
and other loads benefiting from a controlled output
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
8
3152.2004.12.0.9
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
