MIC2846A Datasheet, PDF (12/19 Pages) Micrel Semiconductor – High Efficiency 6 Channel Linear WLED Driver with DAM™, Digital Control and Dual Low IQ LDOs

Micrel Inc.
MIC2846A
Application Information
Brightness Level
(0 - 48)
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
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
Average
Duty
Cycle (%)
100
80
60
48.33
36.67
29.17
21.67
16.67
11.67
9.17
6.67
5
3.33
2.5
1.67
0.83
0
0.83
0.83
1.25
1.67
2.08
2.5
2.92
3.33
4.17
5
5.83
6.67
7.92
9.17
10.42
11.67
14.17
16.67
19.17
21.67
25.42
29.17
32.92
36.67
42.5
48.33
54.17
60
70
80
90
100
Average
I_LED (mA)
12
9.6
7.2
5.8
4.4
3.5
2.6
2
1.4
1.1
0.8
0.6
0.4
0.3
0.2
0.1
0
0.1
0.17
0.25
0.33
0.42
0.5
0.58
0.67
0.83
1
1.17
1.33
1.58
1.83
2.08
2.33
2.83
3.33
3.83
4.33
5.08
5.83
6.58
7.33
8.5
9.67
10.83
12
14
16
18
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
Dynamic Average Matching (DAM™)
The Dynamic Average Matching™ architecture
multiplexes four voltage references to provide highly
accurate LED current and channel matching. The
MIC2846A achieves industry leading LED channel
matching of 1.5% across the entire dimming range.
High Current Parallel Operation
6
Digital
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 4applications. A single WLED can be
driven with all 6 linear drivers by connecting D1 through
D6 in parallel to the cathode of the WLED as shown in
Figure 3. This will generate a current 6 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 MIC2846A 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 D6 pins are 60°
out of phase from each other to reduce electromagnetic
interference. The MIC2846A 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.
April 2010
12
M9999-041210-D