AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Max Current Register Settings—Address 4
Thermal Protection
The AAT3156 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 VOUT pin.
Data
Max Current
1
2
3
4
20mA Max Scale
30mA Max Scale
15mA Max Scale
Low Current Mode1
Applications Information
Low Current Register Settings—Address 5
LED Selection
Data
D1-D4 (mA)
D5-D6 (mA)
The AAT3156 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT3156 to drive most types of LEDs with for-
ward voltage specifications ranging from 2.0V to
4.3V. LED applications may include main and sub-
LCD display backlighting, camera photo-flash appli-
cations, color (RGB) LEDs, infrared (IR) diodes for
remotes, and other loads benefiting from a con-
trolled output current generated from a varying input
voltage. Since the D1 to D6 constant current sinks
are matched with negligible voltage dependence,
the LED brightness will be matched regardless of
the specific LED forward voltage (VF) levels.
1
2
0
0
0
0
3
0
0
4
0
0
5
0
0.05
0.5
1
6
0
7
0
8
0
2
9
0.05
0.5
1
0
10
11
12
13
14
15
16
0
0
2
0
0.05
0.5
1
0.05
0.5
1
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 AAT3156 make it capable of
driving LEDs with forward voltages as high as 4.3V
at full current from an input supply as low as 3.0V.
Current sinks can be paralleled to drive high-cur-
2
2
Disabled Current Sinks
Current sink inputs that are not used should be dis-
abled. To disable and properly terminate unused
current sink inputs, they must be tied to VOUT. If left
unconnected or terminated to ground, the part will
be forced to operate in 2X charge pump mode.
rent LEDs without complication.
Device Switching Noise Performance
The AAT3156 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 AAT3156 soft-start feature prevents
noise transient effects associated with in-rush cur-
rents during start up of the charge pump circuit.
Properly terminating unused current sink inputs is
important to prevent the charge pump modes from
prematurely activating. When properly terminated,
only a small sense current flows for each disabled
channel. The sense current for each disabled chan-
nel is less than 120µA.
The AAT3156 is also equipped with an "auto-disable"
feature to protect against an LED failure condition.
1. Low Current Mode requires the Max Current register to be set to Low Current Mode. Low Current Mode is unaffected by the settings
for Addresses 1-3.
3156.2005.06.1.1
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