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 MIC4802 is a high efficiency, single channel, White
LED (WLED) driver. This constant current linear device is
designed to drive a single high power WLED up to 800mA
and features a low dropout of 280mV at 800mA (typical).
Brightness is controlled through an Ultra Fast PWM™
interface which can operate from 1% to 100% duty cycle.
The MIC4802 is available in an 8-pin Epad SOIC leaded
package with a junction temperature range of -40°C to
+125°C
Requirements
The MIC4802 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 MIC4802 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, J2 and J3, respectively, paying careful
attention to polarity and supply voltage
(3.0VV
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. V
BAT
is
connected to V
IN
through a 0 resistor, R1.
March 2011
M9999-032111-B
2. Enable/Disable the MIC4802
To enable the device, apply a DC voltage of 1.2V or
greater to the EN pin. This allows for full brightness of
the WLED(s) (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 the datasheet).
Pulling EN low for more than 40ms forces the
MIC4802 into a low I
Q
sleep mode. Do not leave the
EN pin floating as this may cause an indeterminate output
state. A pull up resistor of 10k is placed from EN (JP1)
to V
IN
to ensure that the WLED is ON when an input signal
is applied.
3. Setting LED current with R
SET
resistor.
The average LED current may be calculated using the
equation below:
()
280.0)(
4920
)(
280.0
)(
4920
)(
−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 6.19k which
corresponds to I
LED
of 830mA.
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, D1, should be used when
making dropout measurements with a series ammeter.
Ordering Information
Part Number Description
MIC4802YME EV
Evaluation board with the Single
Channel MIC4802 device
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