Microchip MIC2874YCS Handleiding

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MIC2874 Evaluation Board

1.2A HighBrightness Flash LED Driver with -

Single-Wire Serial Interface

General Description

The MIC287current, highiency flash LED 4 -is a high-effic

driver thatoperate s in both torch and sflash mode.

MIC2874 -has a builtin internally compensated current-

mode PWM 4 MHz boost converter that allows the usage of

very small inductors and output capacitors. It is used to

step upthe supply voltage to a high enough voltage at the

OUT pinto drive the LED current when the supply voltage

is lower than the required output voltage. When the supply

voltage exceeds the required output voltage, the

synchronous switch of the converter is fully turned on and

the LED driver operates in linear mode. 4 MIC287also

features a configurable safety timer thatautomatically

shuts dhe LED current after theset duration haown t s

expired if the programmed LED current exceeds a certain

current threshold. These features make the MIC2874 an

ideal solution for highresolution camera phone LED flash -

light driver applications.

The MIC287n be controlled through the single4 ca-wire

serial interface and/or external control pins. A robust

single-wire serial interface allows simple control by the

host processor to support typical camera functions such as

auto-focus, white balance, and image capture.

Datasheets and support documentation are available on

Micrel’s web site at: www.micrel.com.

Requirements

The MIC2874 evaluation board requires a bench input

power source that is adjustable from 2.7V 5to 5.V and is

able to deliver greater than 4.5 amps at 2.7 volts.

Precautions

The evaluation board does not have reverse polarity

protection. Applying a negative voltage acrossthe PVIN

terminal to PGND terminalmay damage the device. The

MIC287evaluat4 ion board is tailored for a Lithium-ion

range input supply voltage. It should not exceed 5.5V on

the input.

Getting Started

1. P Connect external supply to the VIN terminals.

Apply desired input voltage to the PVIN (J1) and

PGND (J2) terminals of the evaluation board, paying

careful attention to polarity and supply range. Since

the default etection threshold voltage is low-bdattery

3.0V, the supply voltage should be set between 3.0V

and5.5V when testing the MIC287without using 4 the

singleheowattery et-wire interface. T l-bdection

threshold can be set to another value or disabled via

single-wire interface. An ammeter may be connected

between the powerand the supply positive terminal

evaluation board PVIN terminal. Ensure that the

supply voltage is monitored across the PVIN and

PGND terminals. The ammeter and /or power lead

resistance can reduce the input voltage supply.

2. 4. Enable/Disable the MIC287

The MIC287evaluation board has an enable4 (DC) pin

(JP2 J4 or lower pinin idle ). The MIC2874 is enabled

() standbymode when the DCpin is asserted high.

Setting a jumper at JP2 can connect the DC pin to

PVIN. If this pin is driven low for more than 405µs, the

IC will shut down. Alternatively, the IC can be enabled

or disabled by software through single- wire interface.

3. mode. Enable/Disable the flash

The FEN (J5 or JP3 lower pin) isthe flash mode

enable pin. A lowhigh transition at pin initiates --tothis

the flash mode and the safety timer. Setting a jumper

at JPP3 can connect FEN to VIN. If FEN pin is left

floating, it will be pulled down internally by built-µin 1A

current source when the device is enabled.

Alternatively, the can be enabled or flash mode

disabled by software through single- wireinterface.

4. Graphic user interface support.

Graphical user interface software can be used with the

MICUSB Dongle EV for configuringand testing of the

MIC2874 with a standard computer. For more detail,

refer to the MIC2874 Evaluation Softwaresection.

Ordering Information

Part Number Description

MIC287MIC2874Y EV CS4 Evaluation Board

MICUSB I2C Serial Programmer Board

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

August 27, 2014 Revision 1.0

Product specificaties