MIC2860-D_11 Datasheet, PDF (6/12 Pages) Micrel Semiconductor – High Efficiency 2 Channel WLED Driver with Single Wire Digital Control

Micrel Inc.
Functional Diagram
MIC2860-2D
Figure 1. MIC2860-2D Functional Block Diagram
Functional Description
The MIC2860-2D is a 2 channel WLED driver. The
WLED driver is designed to maintain proper current
regulation with LED current accuracy of 1.0% while the
typical matching between the 2 channels is 0.5% at
room temperature. The WLEDs are driven independently
from the input supply and will maintain regulation with a
dropout of 52mV at 30.2mA. The low dropout of the
linear drivers allows the WLEDs to be driven directly
from the battery voltage and eliminates the need for
large and inefficient charge pumps. The maximum
WLED current for each channel is set via an external
resistor.
Block Diagram
As shown in Figure 1, the MIC2860-2D consists of 2
current mirrors set to copy a master current determined
by R_SET. The linear drivers have a designated control
block for enabling and dimming of the WLEDs. The
MIC2860-2D dimming is controlled by an internal Digital
Control Interface.
V_IN
The input supply (V_IN) provides power to the linear
drivers and the control circuitry. The V_IN operating range
is 3V to 5.5V. Due to wire inductance a minimum bypass
capacitor of 1µF should be placed close to the input (V_IN)
pin and the ground (GND) pin. Refer to the layout
recommendations section for details on placing the input
capacitor (C1).
SC
The SC pin is equivalent to the enable pin for the linear
drivers on the MIC2860-2D. It can also be used for
dimming using a single wire digital interface. See the
MIC2860-2D Digital Dimming Interface in the Application
Information section for details. Do not leave control pins
floating.
R_SET
The R_SET pin is used by connecting an R_SET resistor to
ground to set the peak current of the linear drivers. The
maximum LED current set by the R_SET resistor is shown
in the table below:
R_SET (kΩ)
9.53
11.5
14.3
15.8
19.1
28.7
I_LED (mA)
30.2
25.0
20.1
18.2
15.1
10.0
Table 1. Maximum LED Current vs. R_SET Resistor Values
A plot of maximum I_LED versus R_SET is shown in Figure 2.
Peak LED Current
vs. R_SET
35
30
25
20
15
10
5
0
8 12 16 20 24 28 32
R_SET (kΩ)
Figure 2. Peak LED current vs. R_SET
July 2010
6
M9999-072010-A