MIC2874YCS datasheet(12/22 Pages) MICREL

12 / 22 page

Micrel, Inc.

MIC2874

Application Information

MIC2874 can drive a high-current flash WLED in either

flash mode or torch mode.

Boost Converter

The internal boost converter is turned on/off automatically

when the LED driver is activated/de-activated without any

exception.

The boost converter is an internally-compensated current-

mode PWM boost converter running at 4MHz. It is for

stepping up the supply voltage to a high enough value at

the OUT pin to drive the LED current. If the supply voltage

is high enough, the synchronous switch of the converter is

then fully turned on. In this case, all the excessive voltage

is dropped over the linear LED driver.

Flash Mode

The maximum and default current levels in the flash mode

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

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

flash control register (address 1),

for the desired flash

duration, subjected to the safety timeout setting. The flash

mode current is terminated when the FEN pin is brought

low and the flash register is cleared, or when the

configurable safety timer expires.

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 register is

cleared or when the configurable safety timer 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 torch current in the torch control

Configurable Safety Timer

The flash 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

(addresses 3 and 5).

Low-Battery Voltage Detection (LBVD)

When the VIN voltage drops below the LBVD threshold

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

driver is disabled. The LED driver can be resumed by

raising the VIN above the LBVD threshold and toggling the

corresponding flash or torch command. The LBVD

threshold is adjustable thru the LBVD control register

(address 4).

Overvoltage Protection

When the output voltage rises above an internal OVP

threshold, MIC2874 is latched off automatically to avoid

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

Each time before enabling the LED driver, the MIC2874

performs the short circuit test by driving the flash LED with

a small (2mA typical) current for 200

µs. If (V

OUT – VLED) is

less than 1.7V at the end of the short-circuit test, then the

LED is considered to be shorted and MIC2874 will ignore

the flash 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

°C and either FEN pin, FEN register, TEN

Single-Wire Interface

The single-wire interface allows the use of a single

multiplexed enable and data pin (DC) for control and

communication in GPIO limited applications. The interface

is implemented using a simple mechanism allowing any

open drain or directly driven GPIO to control the MIC2874.

The MIC2874 uses the single-wire interface for simple

command and control functions. The interface provides

fast access to write only registers with protection features

to avoid potentially erroneous data writes and improve

robustness. When DC is in a low state and no data is

detected

for

longer

than

405µs,

the

MIC2874

will

automatically go into a low-power SHUTDOWN state,

simultaneously resetting internal registers to default states.

Overview

The single-wire interface relies on a combination of bit

edges and the period between edges in order to

communicate

across

single

wire.

Each

word

transmitted as a series of pulses, with each pulse

incrementing an internal data counter. A stop sequence

consisting of an inactive period of DC pin remaining high is

used to latch the data word internally. An address and data

framing format is used to improve protection against

erroneous writes by enforcing address and data field

lengths as well as the timing duration between them.

Timing is designed such that when communicating with a

device using a low cost on chip oscillator, the worst case

minimum and maximum conditions can be easily met

within the wide operating range of the oscillator. Using this

method guarantees that the device can always detect the

delay introduced by the communication master.

August 26, 2014

Revision 1.0

MIC2874YCS Datasheet(PDF) 12 Page - Micrel Semiconductor

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