AAT3140 Datasheet, PDF (11/16 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications

AAT3140
High Efficiency 1X/1.5X/2X Charge Pump
for White LED Applications
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_F) for the LED being driven.
Since the output current of the AAT3140 is pro-
grammable, 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 (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 programmability
and real-time control of LED brightness.
The individual current level settings are each
approximately 1dB apart for settings above Code 8
(see Current Level Settings below). The current
level settings below Code 8 are more than 1dB
apart and serve the needs for transmissive dis-
plays and other low-current applications.
Normalized Current Level Settings
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
Constant Current Source Output Nominal Programming Levels (mA)
Code
1
2
3
4
5
6
7
8
I_OU(mT (Aty)p)
0.0
0.1
0.2
0.4
0.5
0.7
1.1
1.8
Code
9
10
11
12
13
14
15
16
I_OU(mT (Aty)p)
2.0
2.2
2.5
2.8
3.2
3.5
4.0
4.5
Code
17
18
19
20
21
22
23
24
I_OU(mT (Aty)p)
5.1
5.6
6
7
8
9
10
12
Code
25
26
27
28
29
30
31
32
I_OU(mT (Aty)p)
13
15
17
19
21
24
27
30
3140.2005.03.1.1
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