AAT3140_07 ANALOGICTECH [Advanced Analogic Technologies], AAT3140_07 Datasheet - Page 11

• Manufacturer Part Number: AAT3140_07
• Description: High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

Applications Information
Constant Current Output Level Settings
The constant current source amplitudes for D1 to D4
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 D4 are true independent
constant current sources, the voltage observed on
any single given output will be determined by the
actual forward voltage (V
Since the output current of the AAT3140 is pro-
grammable, no PWM (pulse width modulation) or
additional control circuitry are needed to control
3140.2007.03.1.3
Code
1
2
3
4
5
6
7
8
Table 1: Constant Current Source Output Nominal Programming Levels.
1.00
0.10
0.01
0.00
I
1
OUT
(mA)
2
0.0
0.1
0.2
0.4
0.5
0.7
1.1
1.8
(typ)
F
3
) for the LED being driven.
4
5
Figure 1: Normalized Current Level Settings.
6
Code
7
10
11
12
13
14
15
16
9
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
I
OUT
(mA)
2.0
2.2
2.5
2.8
3.2
3.5
4.0
4.5
(typ)
High Efficiency 1X/1.5X/2X Charge Pump
Code
Code
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 AAT3140
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 for transmissive displays and other low-cur-
rent applications.
17
18
19
20
21
22
23
24
I
OUT
for White LED Applications
(mA)
5.1
5.6
10
12
6
7
8
9
(typ)
Code
25
26
27
28
29
30
31
32
AAT3140
I
OUT
(mA)
13
15
17
19
21
24
27
30
(typ)
11