Microchip MIC2874YCS Handleiding

Microchip Niet gecategoriseerd MIC2874YCS

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MIC2874 Evaluation Board
1.2A High Brightness Flash LED Driver with -
Single-Wire Serial Interface
General Description
The MIC287 current, high iency flash LED 4 -is a high -effic
driver that operate s in both torch and sflash mode .
MIC2874 -has a built in internally compensated current-
mode PWM 4 MHz boost converter that allows the usage of
very small inductors and output capacitors. It is used to
step up the supply voltage to a high enough voltage at the
OUT pin to drive the LED current when the supply voltage
is lower than the required output voltage. When the supply
voltage exceeds the required output voltage, the
synchronous switch of the converter is fully turned on and
the LED driver operates in linear mode. 4 MIC287 also
features a configurable safety timer that automatically
shuts d he LED current after the set duration haown t s
expired if the programmed LED current exceeds a certain
current threshold. These features make the MIC2874 an
ideal solution for high resolution camera phone LED flash -
light driver applications.
The MIC287 n be controlled through the single4 ca -wire
serial interface and/or external control pins. A robust
single-wire serial interface allows simple control by the
host processor to support typical camera functions such as
auto-focus, white balance, and image capture.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Requirements
The MIC2874 evaluation board requires a bench input
power source that is adjustable from 2.7V 5to 5. V and is
able to deliver greater than 4.5 amps at 2.7 volts.
Precautions
The evaluation board does not have reverse polarity
protection. Applying a negative voltage across the PVIN
terminal to PGND terminal may damage the device. The
MIC287 evaluat4 ion board is tailored for a Lithium-ion
range input supply voltage. It should not exceed 5.5V on
the input.
Getting Started
1. P Connect external supply to the VIN terminals.
Apply desired input voltage to the PVIN (J1) and
PGND (J2) terminals of the evaluation board, paying
careful attention to polarity and supply range. Since
the default etection threshold voltage is low-b dattery
3.0V, the supply voltage should be set between 3.0V
and 5.5V when testing the MIC287 without using 4 the
single he ow attery et-wire interface. T l -b d ection
threshold can be set to another value or disabled via
single-wire interface. An ammeter may be connected
between the power and the supply positive terminal
evaluation board PVIN terminal. Ensure that the
supply voltage is monitored across the PVIN and
PGND terminals. The ammeter and /or power lead
resistance can reduce the input voltage supply.
2. 4. Enable/Disable the MIC287
The MIC287 evaluation board has an enable4 (DC) pin
( JP2 J4 or lower pin in idle ). The MIC2874 is enabled
( ) standby mode when the DC pin is asserted high.
Setting a jumper at JP2 can connect the DC pin to
PVIN. If this pin is driven low for more than 405µs, the
IC will shut down. Alternatively, the IC can be enabled
or disabled by software through single- wire interface.
3. mode. Enable/Disable the flash
The FEN (J5 or JP3 lower pin) is the flash mode
enable pin. A low high transition at pin initiates - -to this
the flash mode and the safety timer. Setting a jumper
at J PP3 can connect FEN to VIN. If FEN pin is left
floating, it will be pulled down internally by built- µin 1 A
current source when the device is enabled.
Alternatively, the can be enabled or flash mode
disabled by software through single- wire interface.
4. Graphic user interface support.
Graphical user interface software can be used with the
MICUSB Dongle EV for configuring and testing of the
MIC2874 with a standard computer. For more detail,
refer to the MIC2874 Evaluation Software section.
Ordering Information
Part Number Description
MIC287 MIC2874Y EV CS 4 Evaluation Board
MICUSB I2C Serial Programmer Board
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
August 27, 2014 Revision 1.0
Micrel, Inc.
MIC2874 Evaluation Board
Evaluation Board Description
Figure 1 4 . MIC287 Evaluation Board
Flash Mode
The maximum and default current level in the flash mode s
are 1.2A and 1A respectively The flash mode current can .
be initiated by asserting , or by setting the the FEN pin high
flash control register (address 1) through the single -wire
interface for the desired f ash duration, l which is subjected
to the safety timeout setting. The flash mode current is
terminated when the FEN and the flash pin is brought low
r egister is cleared, or when the configurable safety timer
expires.
The 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 either
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 t n the torch control orch current i
register (address le-2) through the sing wire serial
interface.
Congurable Safety Timer
The 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
(a ddresses 3 and 5).
Low- Battery Voltage Detection (LBVD)
When the VIN voltage drops below the LBVD threshold
(default = 3.0 V) in flash or torch mode, the LED current
driver is disabled D driver can be resumed by . The LE
raising the VIN above the LVBD threshold and toggling the
corresponding flash or torch command. The LBVD
threshold is adjustable thru the LBVD control register
(a . ddress 4)
Overvoltage Protection
When the output voltage rises above an internal OVP
threshold, MIC287 is latched off automatically to avoid 4
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
T 4 a -he MIC287 performs short circuit test by driving the
flash LED with a small (2mA typical) current for 200µs
every time it begins to enable the LED driver. If (VOUT –
VLED) < 1.7V circuit test, the LED is at the end of the short -
considered to be shorted and MIC2874 fwill ignore the lash
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 and either FEN pin, FEN register, TEN °C
register, or VIN is toggled.
August 27, 2014 2 R evision 1.0
Micrel, Inc.
MIC2874 Evaluation Board
Single- Wire Interface
The single wire interface allows the use of - one 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 MIC287 wire interface for simple 4 uses the single-
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 4 w, the MIC287 ill
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,
which consists of an inactive period where the DC pin
remain highs , 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.
T he t of the MIC2874 iming is designed to easily meet a
wide operating range when communicating with a device
using a low cost on chip oscillator Using this method .
guarantees that the device can always detect the delay
introduced by the communication master.
Idle States and Error Conditions
In shutdown mode, the MIC2874 is in a reset condition
with all functions off while consuming minimal power.
Register settings are reset to default state when coming
out of shutdown state. In idle mode, all register settings
persist and all MIC2874 functions continue in their current
state. Table 1 summarizes the difference between the two
idle modes:
Table 1. Differences between Idle Modes
Mode Shutdown Idle
VDC Low High
ISUPPLY
(all functions o)
1μA 230μA
Register State Default Persist
Start- Up Time 1μs 100ns
Idle mode is entered automatically at the end of a
communication frame by holding DC high for ≥T END,
enabling the device by bringing DC high when in shutdown
mode, or when an error is detected by the single-wire
interface logic.
Shutdown mode can be entered at any time by pulling
down DC for ≥TEND, discarding any current communication
and res nternal registers. etting the i If a communication is
received between the T LAT period and the shutdown
period, the communication is discarded. This state is also
used to create an internal error state to avoid erroneously
latching data where the communication process cannot be
serviced in time. Each register has a maximum value
associated with it. If the number of bits clocked in exceeds
the maximum value for the register, the data is assumed to
be an error and the data is discarded.
V
H
V
L
T
END
SHUTDOWN IDLE
T
END
T
LAT
IDLE
V
H
V
L
T
LAT
V
H
V
L
T
END
T
LAT
< T
END
- T
LAT
IDLE
Figure 2. Abort, Shutdown, and Idle Timing Waveforms
August 27, 2014 3 R evision 1.0

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: MIC2874YCS

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