Microchip MIC2874YCS Manual

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Side 1/16

MIC2874 Evaluation Board

1.2A High Brightness Flash LED Driver with -

Single-Wire Serial Interface

General Description

The MIC287 current, high iency flash LED 4 -is a high -effic

driver that operate s in both torch and sflash mode .

MIC2874 -has a built in 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 up the supply voltage to a high enough voltage at the

OUT pin to 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 MIC287 also

features a configurable safety timer that automatically

shuts d he LED current after the set duration haown t s

expired if the programmed LED current exceeds a certain

current threshold. These features make the MIC2874 an

ideal solution for high resolution camera phone LED flash -

light driver applications.

The MIC287 n 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 across the PVIN

terminal to PGND terminal may damage the device. The

MIC287 evaluat4 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-b dattery

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

and 5.5V when testing the MIC287 without using 4 the

single he ow attery et-wire interface. T l -b d ection

threshold can be set to another value or disabled via

single-wire interface. An ammeter may be connected

between the power and 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 MIC287 evaluation board has an enable4 (DC) pin

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

( ) standby mode when the DC pin 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) is the flash mode

enable pin. A low high transition at pin initiates - -to this

the flash mode and the safety timer. Setting a jumper

at J PP3 can connect FEN to VIN. If FEN pin is left

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

current source when the device is enabled.

Alternatively, the can be enabled or flash mode

disabled by software through single- wire interface.

4. Graphic user interface support.

Graphical user interface software can be used with the

MICUSB Dongle EV for configuring and testing of the

MIC2874 with a standard computer. For more detail,

refer to the MIC2874 Evaluation Software section.

Ordering Information

Part Number Description

MIC287 MIC2874Y EV CS 4 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

Micrel, Inc.

MIC2874 Evaluation Board

Evaluation Board Description

Figure 1 4 . MIC287 Evaluation Board

Flash Mode

The maximum and default current level in the flash mode s

are 1.2A and 1A respectively The flash mode current can .

be initiated by asserting , or by setting the the FEN pin high

flash control register (address 1) through the single -wire

interface for the desired f ash duration, l which is subjected

to the safety timeout setting. The flash mode current is

terminated when the FEN and the flash pin is brought low

r egister is cleared, or when the configurable safety timer

expires.

The flash mode current can be adjusted to a fraction of the

maximum flash mode current level by selecting the desired

value in the flash control register through the single-wire

serial interface.

Torch Mode

By default, the maximum torch mode level is 300mA. The

torch mode operation is activated by setting the torch

control register (address 2) for the desired duration. The

torch mode current is terminated when the torch either

expires.

Like the flash mode current, the torch mode current can be

set to a fraction of the maximum torch mode current level

by selecting the desired t n the torch control orch current i

interface.

Congurable Safety Timer

The safety timeout feature automatically shuts down the

LED current after the safety timer duration is expired if the

programmed LED current exceeds a certain current

threshold. Both the current threshold and the timer

duration are programmable via the safety timer registers

(a ddresses 3 and 5).

Low- Battery Voltage Detection (LBVD)

When the VIN voltage drops below the LBVD threshold

(default = 3.0 V) in flash or torch mode, the LED current

driver is disabled D driver can be resumed by . The LE

raising the VIN above the LVBD threshold and toggling the

corresponding flash or torch command. The LBVD

threshold is adjustable thru the LBVD control register

(a . ddress 4)

Overvoltage Protection

When the output voltage rises above an internal OVP

threshold, MIC287 is latched off automatically to avoid 4

permanent damage to the IC. To clear the latched off

condition, either power cycle the MIC2874 or assert the

DC pin low.

Short-Circuit Detection

T 4 a -he MIC287 performs short circuit test by driving the

flash LED with a small (2mA typical) current for 200µs

every time it begins to enable the LED driver. If (VOUT –

VLED) < 1.7V circuit test, the LED is at the end of the short -

considered to be shorted and MIC2874 fwill ignore the lash

and/or torch mode command. Note that the short-circuit

test is carried out every time prior to flash and torch mode,

but the result is not latched.

Thermal Shutdown

When the internal die temperature of MIC2874 reaches

155°C, the LED driver is disabled until the die temperature

falls below 140 and either FEN pin, FEN register, TEN °C

August 27, 2014 2 R evision 1.0

Produkt Specifikationer

Mærke:	Microchip
Kategori:	Ikke kategoriseret
Model:	MIC2874YCS

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