MIC2874YCS datasheet(11/22 Pages) MICREL

11 / 22 page

Micrel, Inc.

MIC2874

Functional Description

VIN

The input supply provides power to the internal MOSFETs

gate drive and controls circuitry for the switch-mode

regulator. The operating input voltage range is from 2.7V

to 5.5V. A 4.7µF low-ESR ceramic input capacitor should

be connected from VIN to AGND as close to MIC2874 as

possible to ensure a clean supply voltage for the device.

The minimum voltage rating of 10V is recommended for

the input capacitor.

The MIC2874 has internal low-side and synchronous

MOSFET switches. The switch node (SW) between the

internal MOSFET switches connects directly to one end of

the inductor and provides the current paths during

switching cycles.

The other end of the inductor is connected to the input

supply voltage. Due to the high-speed switching on this

pin, the switch node should be routed away from sensitive

nodes wherever possible.

LGND

This is the ground path of the LED current sink. It should

be connected to the AGND on the PCB. The current loop

of the analog ground should be separated from that of the

power ground (PGND). LGND and AGND should be

connected to PGND at a single point.

AGND

This is the ground path for the internal biasing and control

circuitry. AGND should be connected to the LGND directly.

The current loop of the analog ground should be separated

from that of the power ground (PGND). The AGND and

LGND should be connected to PGND at a single point.

PGND

The power ground pin is the ground path for the high

current in the boost switch. The current loop for the power

ground should be as small as possible and separate from

the analog ground (AGND) loop as applicable.

OUT

Boost converter output pin which is connected to the

anode of the LED. A low-ESR ceramic capacitor of 4.7µF

or larger should be connected from OUT to PGND as

close as possible to the MIC2874. The minimum voltage

rating of 10V is recommended for the output capacitor.

LED

The current sink pin for the LED. The LED anode is

connected to the OUT pin and the LED cathode is

connected to this pin.

The DC is a single multiplexed device enable and serial

data

control

used

for

functional

control

and

communication in GPIO limited applications. When the DC

pin is used as a hardware device enable pin, a logic high

signal on the DC pin enables the device, and a logic low

signal on the DC pin disables the device. When the DC pin

is used as the single-wire serial interface digital control pin,

a combination of bit edges and the period between edges

is used to communicate a variable length data word across

the single wire. Each word is transmitted as a series of

pulses, with each pulse incrementing an internal data

counter. A stop sequence consisting of an inactive period

is used to latch the data word internally. Two data words in

series received are then used to set a specific register with

specific

value

for

controlling

specific

function.

The

MIC2874 supports five writeable registers for controlling

flash mode, torch mode, safety timer duration, safety timer

threshold current, and low-battery threshold.

An address/data frame is used to improve protection

against erroneous writes where communications are in

error. 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 all internal registers to their default states.

FEN

FEN is the hardware enable pin for flash mode. A logic

low-to-high transition on FEN pin can initiate the MIC2874

in flash mode. If FEN is left floating, it is pulled down

internally by a built-in 1µA current source when the device

is enabled. Flash mode is terminated when FEN is pulled

low or left floating, and the flash register is cleared.

August 26, 2014

Revision 1.0

MIC2874YCS Datasheet(PDF) 11 Page - Micrel Semiconductor

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