Ultra Fast PWM and DAM™ Dynamic Average Matching are trademarks of Micrel, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
General Description
The MIC4811 is a high efficiency linear White LED
(WLED) driver; it is designed to drive up to six high current
WLEDs while maintaining constant current in each
channel. The MIC4811 features Dynamic Average
Matching™ (DAM™) which is specifically designed to
provide optimum matching across all WLEDs. These high
accuracy (±1% typical) current regulated WLED channels
ensure uniform display illumination under all conditions. A
typical dropout of 100mV at 50mA is expected.
The MIC4811 is available in a 10-pin MSOP package with
a junction temperature range of -40°C to +125°C.
Datasheets and support documentation can be found on
Micrel’s web site at: www.micrel.com
Requirements
The MIC4811 evaluation board requires a power supply
that is capable of delivering at least 1A while providing an
input voltage between 3.0V and 5.5V.
Precautions
The MIC4811 evaluation board is designed for an input
voltage no greater than 6V. This evaluation board does not
have reverse polarity protection; hence, applying a
negative voltage to the V
IN
terminal may damage the
device.
Getting Started
1. Connect an external supply to V
IN
. Apply the
desired input voltage across V
IN
and ground
terminals, J1 and J2, respectively, paying careful
attention to polarity and supply voltage
(3.0V≤V
IN
≤5.5V). An ammeter may be placed
between the input supply and the V
IN
terminal to
the evaluation board. Ensure that the supply
voltage is monitored at the V
IN
terminal. The
ammeter and/or power lead resistance can reduce
the voltage supplied to the input.
2. Enable/Disable the MIC4811
To enable the device, apply a DC voltage of 1.2V or
greater to the EN pin (J3). This allows for full
brightness of the WLEDs (100% duty cycle). The EN
pin can also be used for dimming by connecting a
PWM signal and varying its duty cycle (please refer to
the Ultra Fast PWM™ Dimming Interface Section in
datasheet). Pulling EN low for more than 20ms forces
the MIC4811 into a low I
Q
sleep mode. Do not leave
the EN pin floating as this may cause an indeterminate
output state. A pull down resistor of 200kΩ is placed from
EN to GND to ensure that the WLEDs are OFF when an
enable signal is not applied.
3. Setting LED current with R
SET
resistor.
The average LED current may be calculated using the
equation below:
()
139.0)(
820
)(
139.0
)(
820
)(
−Ω
⋅
=
+
⋅
=Ω
kR
D
mAI
mAI
D
kR
SET
LED
LED
SET
D is the duty cycle of the LED current during PWM
dimming; D=1 when device is fully ON. The stock
evaluation board uses an R
SET
value of 16.5kΩ which
corresponds to I
LED
of 50mA.
4. Measuring WLED current.
To measure WLED current, simply insert an ammeter
in series with the WLED(s). Keep in mind that a series
ammeter will add a small voltage drop, so the voltage
at the WLED terminal(s), D1-D6, should be used when
making dropout measurements with a series ammeter.
Ordering Information
Part Number Description
MIC4811YMM EV
Evaluation board with Six Channel
WLED Driver
March 2011
M9999-032111-B
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