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MIC2844A View Datasheet(PDF) - Micrel

Part Name
Description
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MIC2844A Datasheet PDF : 14 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
Micrel Inc.
Application Information
Brightness Level
(0 - 48)
Average
Duty
Cycle (%)
Average
ILED (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
IPEAK (mA)
60% of IPEAK
RSET = 20.5k
IPEAK = 12mA
0
60% of IPEAK
100% of IPEAK
RSET = 20.5k
IPEAK = 20mA
Table 1. Digital Interface Brightness Level Table
August 2009
MIC2844A
Dynamic Average Matching™ (DAM™)
The Dynamic Average Matching™ architecture
multiplexes four voltage references to provide highly
accurate LED current and channel matching. The
MIC2844A achieves industry leading LED channel
matching of 1.5% across the entire dimming range.
High Current Parallel Operation
U1 MIC2844AYMT
VIN
C1
RSET
Low
Dropout
Linear
Driver
DC
Digital
VIN
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 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 MIC2844A 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 for a single channel at
different brightness levels. When dimming, the D1
through D6 pins are 60° out of phase from each other to
reduce electromagnetic interference. The MIC2844A
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.
8
M9999-080309-D
 

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