MIC2873 Datasheet, PDF (12/24 Pages) Micrel Semiconductor – 1.2A High-Brightness Flash LED Driver with Single-Wire Serial Interface

Micrel, Inc.
MIC2873
Application Information
MIC2873 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 2MHz. 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 current level in the flash mode is 1.2A. 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
register (Address 2) via the single-wire serial interface.
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, MIC2873 is latched off automatically to avoid
permanent damage to the IC. To clear the latched off
condition, either power cycle the MIC2873 or assert the
DC pin low.
Short-Circuit Detection
Each time before enabling the LED driver, the MIC2873
performs the short circuit test by driving the flash LED with
a small (2mA typical) current for 200µs. If (V_OUT – V_LED) <
1.7V at the end of the short-circuit test, the LED is
considered to be shorted and MIC2873 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 MIC2873 reaches
155°C, the LED driver is disabled until the die temperature
falls below 140°C and either FEN pin, FEN register, TEN
register, or VIN is toggled.
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 MIC2873.
The MIC2873 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 MIC2873 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 a 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 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.
July 17, 2014
12
Revision 1.0