MIC2860_D Datasheet, PDF (8/12 Pages) Micrel Semiconductor – High Efficiency 2 Channel WLED Driver with Single Wire Digital Control

Micrel Inc.
Application Information
Digital Dimming Interface
Brightness
Level (0 - 31)
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
I_LED (mA)
R_SET=14.3kΩ
20.1
19.4
18.8
18.2
17.5
16.8
16.2
15.6
14.9
14.2
13.6
13.0
12.3
11.6
11.0
10.4
9.7
9.1
8.5
7.8
7.1
6.5
5.9
5.2
4.5
3.9
3.3
2.6
1.9
1.3
0.7
0.3
I_LED (mA)
R_SET=19.1kΩ
15.1
14.6
14.1
13.6
13.1
12.6
12.2
11.7
11.2
10.7
10.2
9.7
9.2
8.7
8.3
7.8
7.3
6.8
6.4
5.8
5.3
4.8
4.4
3.9
3.4
2.9
2.4
1.9
1.4
0.9
0.5
0.2
% of Max.
Current
100
96.7
93.7
90.4
87.1
83.8
80.8
77.5
74.2
70.9
67.9
64.6
61.3
57.9
55.0
51.7
48.3
45.0
42.1
38.7
35.4
32.1
29.1
25.8
22.5
19.2
16.2
12.9
9.6
6.3
3.3
1.7
Table 2. Digital Interface Brightness Level Table
The MIC2860-2D incorporates an easy to use single
wire, serial programming interface that allows users to
set WLED brightness up to 32 different levels as shown
in Table 2. To calculate the brightness level for other
R_SET values, multiply the percentage of max current
values by the maximum LED current set by the R_SET
resistor value from table 1.
For example with R_SET = 19.1kΩ, the max current
(brightness level = 31) is 15.1mA and brightness level 20
would equate to 15.1mA x 0.646 = 9.7mA.
July 2010
MIC2860-2D
Brightness levels are linearly spaced with a maximum
current equal to 100% of the current set by R_SET. The
MIC2860-2D is designed to receive programming pulses
to decrease brightness from the initial start up default
(level 1 maximum current). Once the brightness change
signal is received, the SC pin is simply pulled high to
maintain the brightness. This “set and forget” feature
relieves processor computing power by eliminating the
need to constantly send a PWM signal to the dimming
pin.
Start Up
Assuming the MIC2860-2D has been off for a long time,
the MIC2860-2D will start-up in its default mode
approximately 33µs (t_{START_UP}) after a logic level high is
applied to the SC pin. In the default mode the WLEDs
are turned on at the maximum brightness (level 31).
Each falling edge will cause the default brightness level
to decrease by one.
Figure 3. Typical Start-Up Timing
Shutdown
When the SC input pin is pulled low for a period greater
than or equal to t_SHUTDOWN (500µs), the MIC2860-2D will
turn off the current sinks as shown in Figure 4.
Figure 4. Shutdown Timing
Once the device is shutdown, the control circuit supply is
disabled and the WLEDs are turned off drawing only
0.01µA. Brightness level information stored in the
MIC2860-2D prior to shutdown will be erased and upon
a following startup signal the WLEDs will be turned on at
maximum brightness (level 31).
Programming the Brightness Level
MIC2860-2D is designed to start driving the WLEDs
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M9999-072010-A