AAT3142
High Efficiency 1X/1.5X/2X Charge Pump
for White LED Applications
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.
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 (VF) for the LED being driven.
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.
Since the output current of the AAT3142 is pro-
grammable, no PWM (pulse width modulation) or
additional control circuitry are needed to control
1.00
0.10
0.01
0.00
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
Figure 1: Normalized Current Level Settings.
IOUT (typ)
(mA)
IOUT (typ)
(mA)
IOUT (typ)
(mA)
IOUT (typ)
(mA)
Code
Code
Code
Code
1
2
3
4
5
6
7
8
0.0
0.1
0.2
0.4
0.5
0.7
1.1
1.8
9
2.0
2.2
2.5
2.8
3.2
3.5
4.0
4.5
17
18
19
20
21
22
23
24
5.1
5.6
6
7
8
9
10
12
25
26
27
28
29
30
31
32
13
15
17
19
21
24
27
30
10
11
12
13
14
15
16
Figure 1: Constant Current Source Output Nominal Programming Levels.
3142.2007.03.1.2
11
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
