AAT3152 datasheet(9/12 Pages) AAT

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Constant Current Output Level Settings

The constant current sink levels for D1 to D4 are

set via the serial interface. No PWM (pulse width

modulation) or additional control circuitry is needed

to control LED brightness. This feature greatly

reduces the burden on a microcontroller or system

IC to manage LED or display brightness, allowing

the user to "set it and forget it." With its high-speed

serial interface (up to 1MHz data rate), the input

sink current of the AAT3152 can be changed suc-

cessively to brighten or dim LEDs, giving the users

real-time control of LED brightness. Because the

inputs D1 to D4 are true independent constant cur-

rent sinks, the voltage observed on any single

given input will be determined by the actual forward

voltage (V

F) for the LED being driven.

2Cwire Serial Interface

The current sink input magnitude on the AAT3152 is

controlled by AnalogicTech's S

2Cwire serial digital

input. It relies on the number of rising edges of the

EN/SET pin to address and load the registers.

2Cwire latches data or address after the EN/SET

pin has been held high for time T

LAT. The interface

records rising edges of the EN/SET pin and

decodes them into 16 different states, as indicated

in the Current Setting table. There are four bright-

ness levels for main or sub-display group with the

possibility of individually turning ON or OFF each

group. To further optimize power efficiency, the

AAT3152 also offers four low-current levels for dim

LED operation (Data 13-16). During this low-current

mode, the internal supply current reduces to only

80µA typical.

The counter can be clocked at speeds up to 1MHz,

such that intermediate states are not visible. The

first rising edge of EN/SET enables the IC and ini-

tially sets the output LED current to 20mA. Once

the final clock cycle is input for the desired bright-

ness level, the EN/SET pin is held high to maintain

the device output current at the programmed level.

The device is disabled 500µs (T

OFF)

after the

EN/SET pin transitions to a logic low state.

AAT3152 Current Setting

The EN/SET timing is designed to accommodate a

wide range of data rates. After the first rising edge

of EN/SET, the charge pump is enabled and reach-

es full capacity after the soft-start time (T

SS). During

the soft-start time, multiple clock pulses may be

entered on the EN/SET pin to set the final output

current level with a single burst of clocks.

Alternatively, the EN/SET clock pulses may be

entered one at a time to gradually increase the

LED brightness over any desired time period. The

current outputs remain constant as long as

EN/SET remains in a logic high state. The current

outputs are switched off after EN/SET has

remained in a low state for at least the T

OFF timeout

period; then, the AAT3152 enters shutdown mode

and draws less than 1µA from V

IN. Data are reset

to 0 during shutdown.

Main Group

Sub Group

(D1-D3)

(D4)

Data

OUT (mA)

120

214

310

520

614

710

0.05

0.5

AAT3152

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

For White LED Applications

3152.2005.08.1.2

AAT3152 Datasheet(PDF) 9 Page - Advanced Analog Technology, Inc.

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