PRODUCT DATASHEET
AAT3113, AAT3114/14A
ChargePump
TM
High Efficiency 1.5X Fractional Charge Pumps For White LED Applications
EN/SET Serial Interface
The current source output magnitude is controlled by the
EN/SET pin using AnalogicTech’s Simple Serial Control
(S
2
Cwire) interface. The interface records rising edges of
the EN/SET pin and decodes them into 32 individual cur-
rent level settings each 1dB apart. Code 32 is full scale,
and Code 1 is full scale attenuated by 31dB. The modulo
32 interface wraps states back to state 1 after the 32nd
clock, so 1dB of attenuation is achieved by clocking the
EN/SET pin 31 times (see graph titled, “I
DIODE
Response
-9dB to -10dB”). The counter can be clocked at speeds
up to 1MHz, so intermediate states are not visible. The
first rising edge of EN/SET enables the IC and initially
sets the output LED current to -31dB, the lowest setting
equal to 525µA. Once the final clock cycle is input for the
desired brightness level, the EN/SET pin is held high to
maintain the device output current at the programmed
level. The device is disabled 500µs after the EN/SET pin
transitions to a logic low state.
The EN/SET timing is designed to accommodate a wide
range of data rates. After the first rising edge of EN/SET,
the charge pump is enabled and reaches full capacity
after the soft-start time (T
SS
). During the soft-start time,
multiple clock pulses may be entered on the EN/SET pin
to set the final output current level with a single burst of
clocks. Alternatively, the EN/SET clock pulses may be
entered one at a time to gradually increase the LED
brightness over any desired time period. A constant cur-
rent is sourced as long as EN/SET remains in a logic high
state. The current source outputs are switched off after
EN/SET has remained in a low state for at least the t
OFF
timeout period (see Figure 2).
Applications Information
Current Level Settings
LED current level is set via the serial interface according
to a logarithmic scale where each code is 1dB greater
than the previous code. In this manner, the LED bright-
ness appears linear with each increasing code.
Code
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
20mA max
0.549
0.627
0.706
0.784
0.863
1.020
1.098
1.255
1.412
1.569
1.804
1.961
2.275
2.510
2.824
3.137
Code
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
20mA max
3.529
4.000
4.471
5.020
5.647
6.353
7.059
7.922
8.941
10.039
11.216
12.627
14.118
15.843
17.804
20.000
Table 1: Current Level Settings.
1.0
Normalized Current to Full Scale
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
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.
3113.2008.05.1.10
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