MIC2873 Datasheet, PDF (11/24 Pages) Micrel Semiconductor – 1.2A High-Brightness Flash LED Driver with Single-Wire Serial Interface

Micrel, Inc.
MIC2873
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 MIC2873 as
possible to ensure a clean supply voltage for the device.
The minimum voltage rating of 10V is recommended for
the input capacitor.
SW
The MIC2873 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 MIC2873. 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.
DC
The DC is a single multiplexed device enable and serial
data control pin 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
MIC2873 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 MIC2873 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 MIC2873
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.
July 17, 2014
11
Revision 1.0