AAT3131 datasheet(8/14 Pages) AAT

8 / 14 page

AAT3131

High Efficiency 1X/1.5X Fractional

Charge Pump for White LED Applications

3131.2005.12.1.2

such that outputs D1 to D3 can be controlled inde-

pendently of output D4. For Addresses 1 to 8, 9 to

16, 17 to 24, and 25 to 32, outputs D1 to D3 start

at 0mA and increase from 0.5mA to 20mA in three

8dB steps and three 2.5dB steps.

Output D4

remains constant over these address ranges,

which provides orthogonal control of the two chan-

nels. For Addresses 1 to 8, D4 is set to 0mA; for

Addresses 9 to 16, D4 is set to 1mA; for Addresses

17 to 24, D4 is set to 15mA; and for Addresses 25

to 32, D4 is set to 30mA. This is summarized in

Table1 and Figure 1.

The modulo 32 interface wraps states back to State 1

after the 32nd clock. With each EN/SET pulse, the

output current changes to the next setting in the

address decoding. To change settings to the previous

address decoding, 31 EN/SET clock pulses are

required. The counter can be clocked at speeds up to

1MHz, so that intermediate states are not visible. The

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

ly sets the output LED currents to 0mA. Additional

clocks are required to set the desired current level.

Once the final clock cycle is input for the desired

brightness level, the EN/SET pin is held high to main-

tain the device output current at the programmed

level. The device is disabled 500µs after the EN/SET

pin transitions to a logic low state.

Applications Information

Constant Current Output Level Settings

The constant current source output amplitude for

outputs D1 to D3 and D4 are set via the serial inter-

face according to a logarithmic scale. Using a log-

arithmic scale, LED brightness appears linear with

each increasing code count. Because the outputs

D1 to D4 are true independent constant current

sources, the voltage observed on any single given

output will be determined by the actual forward

voltage (V

F) for the LED being driven.

Since the output current of the AAT3131 is program-

mable through its S

2Cwire interface, no PWM (pulse

width modulation) or additional control circuitry are

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."

Furthermore, with its high-speed serial interface

(1MHz data rate), the output current of the AAT3131

can be changed successively to brighten or dim

LEDs in smooth transitions (e.g., to fade out) or in

abrupt steps, giving the user complete programma-

bility and real-time control of LED brightness.

Figure 1: Output Level Current Settings.

Address Code

AAT3131 데이터시트(PDF) 8 Page - Advanced Analog Technology, Inc.

AAT3131 데이터시트(HTML) 8 Page - Advanced Analog Technology, Inc.

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14

데이터시트 다운로드

링크 URL