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AAT3142 Datasheet(PDF) 11 Page - Advanced Analog Technology, Inc. |
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AAT3142 Datasheet(HTML) 11 Page - Advanced Analog Technology, Inc. |
11 / 16 page AAT3142 High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications 3142.2007.03.1.2 11 Applications Information Constant Current Output Level Settings The constant current source amplitudes for D1 to D3 are set via the serial interface according to a loga- rithmic scale where each code is 1dB greater than the previous code. In this manner, LED brightness appears linear with each increasing code count. Because the outputs D1 to D3 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 AAT3142 is pro- grammable, 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." With its high-speed serial interface (1MHz data rate), the output current of the AAT3142 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. The individual current level settings are each approximately 1dB apart for settings above Code 8 (see Figure 1). The current level settings below Code 8 are more than 1dB apart and serve the needs of transmissive displays and other low-cur- rent applications. Figure 1: Normalized Current Level Settings. Figure 1: Constant Current Source Output Nominal Programming Levels. 0.00 0.01 0.10 1.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Code I OUT (typ) I OUT (typ) I OUT (typ) I OUT (typ) Code (mA) Code (mA) Code (mA) Code (mA) 1 0.0 9 2.0 17 5.1 25 13 2 0.1 10 2.2 18 5.6 26 15 3 0.2 11 2.5 19 6 27 17 4 0.4 12 2.8 20 7 28 19 5 0.5 13 3.2 21 8 29 21 6 0.7 14 3.5 22 9 30 24 7 1.1 15 4.0 23 10 31 27 8 1.8 16 4.5 24 12 32 30 |
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