MIC2871 Datasheet, PDF (9/24 Pages) Micrel Semiconductor – 1.2A High-Brightness LED Flash Driver with Single-Wire Serial Interface

Micrel, Inc.
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 2.2µF low-ESR ceramic input capacitor
should be connected from VIN to AGND2 as close to the
MIC2871 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 MIC2871 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.
AGND1
This is the ground path of the LED current sink. It should
be connected to the AGND2, but not via exposed pad, on
the PCB. The current loop of the analog ground should
be separated from that of the power ground (PGND1 and
PGND2). AGND1 and AGND2 should be connected to
PGND1 and PGND2 at a single point.
AGND2
This is the ground path for the internal biasing and control
circuitry. AGND2 should be connected to the PCB pad for
the package exposed pad. AGND2 should be connected
to the AGND1 directly without going through the exposed
pad. The current loop of the analog ground should be
separated from that of the power ground (PGND1 and
PGND2). The AGND2 and AGND1 should be connected
to PGND1 and PGND2 at a single point.
PGND1 and PGND2
The power ground pins are the ground path for the high
current in the boost switch and they are internally
connected together. The current loop for the power
ground should be as small as possible and separate from
the analog ground (AGND) loop as applicable.
MIC2871
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 PGND1 as
close as possible to the MIC2871. 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, each pulse
incrementing an internal data counter. A stop sequence
consisting of an inactive period is used to latch the data
word internally. The data word received is then used to
set the value of the corresponding register for controlling
specific function. The MIC2871 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 an extended period of time, the MIC2871 will
automatically go into a low-power SHUTDOWN state,
simultaneously resetting all internal registers to their
default states.
FEN1 and FEN2
FEN1 and FEN2 are hardware enable pins for flash
mode. FEN1 is logic-OR with FEN2. A logic low-to-high
transition on either FEN1 pin or FEN2 pin can initiate the
MIC2871 in flash mode. If FEN1 or FEN2 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 both FEN1 and FEN2 are pulled low or left floating,
and the flash register is cleared.
May 29, 2013
9
052913-1.0 (while in progress)
Revision 1.0 (final document)