AAT1401 Datasheet, PDF (11/19 Pages) List of Unclassifed Manufacturers – FOUR-CHANNEL DIGITAL STILL CAMERA POWER SUPPLY

DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Application Information
LED Current Setting
The maximum LED current is determined by value of the
external resistor R_SET from 10mA to 31mA. The value of
R_SET is determined by the voltage of R_SET and the LED
current, and can be calculated by:
R_SET
=
V_SET · 258
I_LED
Where V_SET = 1.2V. Table 1 lists examples of standard 1%
metal film R_SET values for different maximum LED current
requirements.
Maximum LED Current (mA)
31
20
15
12
10
R_SET (kΩ)
10
15
20
25
30
Table 1: Examples of Standard 1% R_SET Values for
Setting Maximum LED Current Levels.
LED current dimming is controlled either via the S²Cwire
single-wire interface through the EN/SET pin in 32 steps
or via PWM control with varied duty cycle up to 100kHz
frequency. The S²Cwire interface programs the LED cur-
rent from the maximum LED current set by R_SET to 2%
of the maximum LED current as shown in Table 2.
S²Cwire
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
LED Current
(% I_MAX)
100
97
94
90
87
84
81
77
74
71
68
65
61
58
55
52
S²Cwire
Data
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
LED Current
(% I_MAX)
48
45
42
39
35
32
29
26
23
19
16
13
10
6
3
2
Table 2: S²Cwire Dimming Control
Current Settings.
Figure 2 illustrates the LED current value at different
S²Cwire code settings when R_SET is 15kΩ with a maxi-
mum LED current of 20mA.
22
20
18
16
14
12
10
8
6
4
2
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
ILED (mA)
Figure 2: S²Cwire Dimming Control
at Maximum LED Current (20mA max).
Filtered PWM Dimming
The AAT1401 provides a PWM input as an additional
means of providing dimming control for CABC applica-
tions. The LED current reduces percentage linearly as
the duty cycle decreasing. Frequencies of up to 100kHz
can be applied. To avoid output flicker and noise, the
input control PWM frequency is filtered by the low pass
filter composed of the error amplifier and the external
compensation capacitor.
Figure 3 shows the LED current dimming controlled by
varying the PWM duty cycle at R_SET = 15kΩ.
20
18
16
14
12
10
8
6
4
2
0
100 90 80 70 60 50 40 30 20 10
0
PWM Duty Cycle (%)
Figure 3: Filtered PWM Dimming Duty Cycle vs.
Maximum LED Current (20mA max).
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
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