AAT3142 datasheet(12/16 Pages) AAT

12 / 16 page

AAT3142

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

for White LED Applications

3142.2007.03.1.2

2Cwire Serial Interface

The current source output magnitude is controlled

by the EN/SET pin, using AnalogicTech's S

2Cwire

interface. The interface records rising edges of the

EN/SET pin and decodes them into 32 individual

current level settings with Code 1 reserved for no

current. Once EN/SET has been held in the logic

high state for time T

LAT, the programmed current is

seen at the current source outputs, and the internal

data register is reset to 0. For subsequent current

level programming, the number of rising edges cor-

responding to the desired code must be entered on

the EN/SET pin.

When EN/SET is held low for an amount of time

greater than T

OFF, the AAT3142 enters into shut-

down mode and draws less than 1µA from V

IN. The

internal data register is reset to 0 during shutdown.

2Cwire Serial Interface Timing

EN/SET

n-1

n <= 32

Data Reg

THI

TLO

TLAT

TOFF

LED Selection

The AAT3142 is specifically intended for driving

white LEDs. However, the device design will allow

the AAT3142 to drive most types of LEDs with for-

ward voltage specifications ranging from 1.0V 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 controlled

output-current generated from a varying input-volt-

age. Since the D1 to D3 output current sources are

matched with negligible voltage dependence, the

LED brightness will be matched regardless of the

specific LED forward voltage (V

F) levels.

In some instances (e.g., in high luminous output

applications such as photo flash), it may be neces-

sary to drive high-V

F type LEDs. The low-dropout

current sources in the AAT3142 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.

Outputs can be paralleled to drive high-current

LEDs without complication.

Termination of Unused Current Source

Outputs

If any outputs (D1 to D3) are not used, they should

be terminated by connecting the respective unused

output directly to ground. This is required to assure

correct charge pump mode operation. If a given

unused output is not terminated to ground, it will

appear to the respective output’s feedback control

as an infinite impedance load and the unused con-

stant current source will be set for a maximum volt-

age. Although no current flows from the unused

current source, the voltage sensed at that node

could force the charge pump control to activate the

charge pump when it is not necessary. To prevent

this effect, simply connect the unused constant

current source outputs to ground.

Device Switching Noise Performance

The AAT3142 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 communication

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