Microchip MIC4802YME Handleiding

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MIC4802 Evaluation Board

High Efficiency 800mA Single Channel

Linear WLED Driver with

Ultra Fast PWM™ Control

Ultra Fast PWM is a trademark 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 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 VIN terminal may damage the

device.

Getting Started

1. Connect an external supply to VIN. Apply the

desired input voltage across VIN and ground

terminals, J2 and J3, respectively, paying careful

attention to polarity and supply voltage

(3.0VVIN5.5V). An ammeter may be placed

between the input supply and the VINterminal to

the evaluation board. Ensure that the supply

voltage is monitored at the VIN terminal. The

ammeter and/or power lead resistance can reduce

the voltage supplied to the input. VBAT is

connected to VIN 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 IQ 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 VIN to ensure that the WLED is ON when an input signal

is applied.

3. Setting LED current with RSET 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 RSET value of 6.19k which

corresponds to ILED 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

Product specificaties