MIC2842A Datasheet, PDF (8/14 Pages) Micrel Semiconductor – High Efficiency 4 Channel WLED Driver with DAM™ and Single Wire Digital Control

Micrel Inc.
Application Information
Brightness Level
(0 - 48)
Average
Duty
Cycle (%)
Average
I_LED (mA)
0
100
12
1
80
9.6
2
60
7.2
3
48.33
5.8
4
36.67
4.4
5
29.17
3.5
6
21.67
2.6
7
16.67
2
8
11.67
1.4
9
9.17
1.1
10
6.67
0.8
11
5
0.6
12
3.33
0.4
13
2.5
0.3
14
1.67
0.2
15
0.83
0.1
16
0
0
17
0.83
0.1
18
0.83
0.17
19
1.25
0.25
20
1.67
0.33
21
2.08
0.42
22
2.5
0.5
23
2.92
0.58
24
3.33
0.67
25
4.17
0.83
26
5
1
27
5.83
1.17
28
6.67
1.33
29
7.92
1.58
30
9.17
1.83
31
10.42
2.08
32
11.67
2.33
33
14.17
2.83
34
16.67
3.33
35
19.17
3.83
36
21.67
4.33
37
25.42
5.08
38
29.17
5.83
39
32.92
6.58
40
36.67
7.33
41
42.5
8.5
42
48.33
9.67
43
54.17
10.83
44
60
12
45
70
14
46
80
16
47
90
18
48
100
20
I_PEAK (mA)
60% of I_PEAK
R_SET = 20.5kΩ
I_PEAK = 12mA
0
60% of I_PEAK
100% of I_PEAK
R_SET = 20.5kΩ
I_PEAK = 20mA
Table 1. Digital Interface Brightness Level Table
MIC2842A
Dynamic Average Matching (DAM™)
The Dynamic Average Matching™ architecture
multiplexes four voltage references to provide highly
accurate LED current and channel matching. The
MIC2842A achieves industry leading LED channel
matching of 1.5% across the entire dimming range.
High Current Parallel Operation
U1 MIC2842AYMT
V_IN
C1
R_SET
Low
Dropout
Linear
Driver
DC
Control
Control
Figure 3. High Current LED Driver Circuit
The linear drivers are independent of each other and can
be used individually or paralleled in any combination for
higher current applications. A single WLED can be
driven with all 4 linear drivers by connecting D1 through
D4 in parallel to the cathode of the WLED as shown in
Figure 3. This will generate a current 4 times the
individual channel current and can be used for higher
current WLEDs such as those used in flash or torch
applications.
Digital Dimming
The MIC2842A utilizes an internal dynamic pulse width
to generate an average duty cycle for each brightness
level. By varying the duty cycle the average current
achieves 49 logarithmically spaced brightness levels.
This generates a brightness scale similar to the
perception of brightness seen by the “human eye.”
Figure 4 shows the LED current at different brightness
levels. When dimming, the D1 through D4 pins are 60°
out of phase from each other to reduce electromagnetic
interference. The MIC2842A uses an internal frequency
of approximately 700Hz to dim the WLEDs. With the
period of approximately 1.43ms, the 60° phase shift
equates to a timing offset of 238μs. As shown in Figure
5, brightness level 32 was selected to show the phase
shift across the channels.
August 2009
8
M9999-080309-D