MIC2860_P Datasheet, PDF (8/12 Pages) Micrel Semiconductor – High Efficiency 2 Channel WLED Driver with PWM Control

Micrel Inc.
Functional Description
The MIC2860-2P is a two channel WLED driver. The
WLED driver is designed to maintain proper current
regulation with LED current accuracy of 1% with a typical
matching between the 2 channels of ±0.5%. 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 peak WLED current for each channel is set
via an external resistor. If dimming is desired the
MIC2860-2P can dim via a PWM signal.
Block Diagram
As shown in Figure 1, the MIC2860-2P consists of two
current sinks with the peak current determined by R_SET.
The linear drivers have a designated control block for
enabling and dimming of the WLEDs. The MIC2860-2P
is controlled by the PWM control block that receives
PWM signals for dimming.
VIN
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 input (VIN)
pin and the ground (GND) pin.
EN
The EN pin enables the linear drivers. It can also be
used for dimming with a PWM signal. See the PWM
Dimming Interface in the Application Information section
for details. Do not leave floating.
R_SET
The R_SET pin is used by connecting a R_SET resistor to
ground to set the peak current of the linear drivers. The
maximum LED current (EN = 100% Duty Cycle) 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
MIC2860-2P
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
D1, D2
The D1 and D2 pins are the linear driver inputs for
WLED 1 and 2, respectively. Connect the anodes of the
WLEDs to V_IN and each cathode of the WLEDs to D1
and D2. When operating with a single WLED, D1 and D2
should be connected to the WLED cathode to parallel
the outputs for improved dropout performance.
Paralleling these pins can also be done to drive a higher
current through a single WLED. Do not leave these pins
floating.
GND
The ground pin is the ground path for the linear drivers.
The current loop for the ground should be as small as
possible. The ground of the input capacitor should be
routed with low impedance traces to the GND pin and
made as short as possible.
A plot of I_LED versus R_SET is shown in Figure 2.
September 2010
8
M9999-092710-A