AAT3152 datasheet(10/12 Pages) AAT

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AAT3152

High Efficiency 1X/1.5X/2X Charge Pump

For White LED Applications

3152.2005.08.1.2

Auto-Disable Feature

The AAT3152 is equipped with an auto-disable fea-

ture 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 particular current

sink pin does not drop to a certain threshold. This

feature is very convenient for disabling 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.

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

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.

Capacitor Selection

Careful selection of the four external capacitors

IN, C1, C2, and COUT is important because they will

affect turn-on time, output ripple, and transient per-

2Cwire Serial Interface Timing

EN/SET

n <= 16

Data Reg

LAT

OFF

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