Instrukcja obsługi Microchip MIC2870YFT

Microchip nieskategoryzowany MIC2870YFT

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MIC2870 Evaluation Board
1.5A Synchronous Boost Flash LED Driver
with I
2
C Interface
Micrel Inc. • 2180 Fortune Drive • Jose, CA 95131 • USA • tel +1 (408) 944 0800 • fax + 1 (408) 474 1000 • San - - http://www.micrel.com
September 24, 2013
Revision 1.2
General Description
The MIC2870 is a high current, high efficiency flash LED - -
driver for one or two high brightness camera flash LEDs. -
The LED driver current is generated by an integrated
inductive boost converter with 2MHz switching frequency
which allows the use of very small inductor and output
capacitor. These features make the MIC2870 an ideal
solution for high resolution camera phone LED flash light -
driver applications.
MIC2870 supports two 750mA w LEDs (WLEDs) or a hite-
single 1.5A WLED configuration. When two WLEDs are
connected, their current are matched automatically.s
MIC2870 operates in either flash or torch modes that can
be controlled through either I2C interface or external pins.
The brightness in the flash and torch mode can be
adjusted via two external resistors individually. High-speed
mode I2C interface provides a simple control at a clock
speed up to 3.4MHz to support most camera functions
such as auto focus, white balance, and image c- apture.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Requirements
The MIC2870 evaluation board requires a bench input
power source that is adjustable from 2.7V to 5.0V and is
able to deliver greater than 4.5A at 2.7V.
Precautions
The evaluation board does not have reverse polarity
protection. Applying a negative voltage across the VIN
terminal to GND terminal may damage the device. The
MIC2870 evaluation board is tailored for a Li ion range -
input supply voltage. It should not exceed 5.0V on the
input.
Getting Started
1. Connect external supply to the VIN terminals.
Apply desired input voltage to the VIN (J1) and ground
(J2) terminals of the evaluation board, paying careful
attention to polarity and supply range (2.7V to 5.0V).
An ammeter may be placed between the power supply
and the input terminal of the evaluation board. Ensure
that the supply voltage is monitored at the input
terminals. The r and /or power lead resistance ammete
can reduce the voltage supplied to the input.
2. Enable/Disable the MIC2870.
The MIC2870 evaluation board has an enable (EN) pin
(J5). The MIC2870 is in standby mode when the EN
pin is asserted . Setting a jumper at TP1 can high
connect the high resistor. EN pin to VIN through a pull-
If this pin is driven low for more than 1s, the IC is
shutdown. This pin is pulled down by an internal
resistor. Alternatively, the IC can be enabled or
disabled by software through I2C interface.
3. Enable/Disable the torch mode.
The TEN (J3) is the torch mode enable pin. When this
pin is high, torch m Setting a jumper the ode is initiated.
at TP4 can connect TEN pin to VIN through a resistor.
If this pin is left floating, -it is pulled down internally by a
built-in 1µA current source when the device is
enabled. Alternatively, the torch mode can be enabled
or disabled by software through I2C interface.
4. Enable/Disable the flash mode.
The FEN (TP2 upper pin) is the flash mode enable pin.
A low- -to high transition at this pin initiates the flash
mode and the flash mode timer. Setting a jumper at
TP2 can connect FEN to VIN through a resistor. If this
pin is left floating, -it is pulled down internally by a built-
in 1µA current source when the device is enabled.
Alternatively, the flash mode can be enabled or
disabled by software through I2C interface.
Ordering Information
Part Number Description
MIC2870YFT EV MIC2870 Evaluation Board
MICUSB Dongle EV I2C Serial Programmer Board
Micrel, Inc.
MIC2870 Evaluation Board
September 24, 2013
2 Revision 1.2
Getting Started (Continued)
5. Enable/Disable flash inhibit.
The FI (TP3 upper pin) is the flash inhibit pin. When
this pin is high in flash mode, both LED1 (D1) and
LED2 (D2) currents are changed from the flash mode
current level to the torch mode current level. When this
pin is low, both LED1 (D1) and LED2 (D2) currents are
changed from torch mode current level back to the
original flash mode current level. Setting a jumper at
TP3 can connect FI to VIN through a resistor. If this
pin is left floating, -it is pulled down internally by a built-
in 1µA current source when the device is enabled.
6. Graphic user interface support.
Graphical user interface software can be used with the
MICUSB Dongle EV allowing configuration and testing
of the MIC2870 with a standard computer. For more
detail, refer to the Evaluation Software section.
Micrel, Inc.
MIC2870 Evaluation Board
September 24, 2013
3 Revision 1.2
Evaluation Board Description
Figure 1. MIC2870 Evaluation Board
Flash Mode
The maximum current level in the flash mode is 750mA
per channel. This current level can be adjusted through an
external resistor connecting to the FRSET pin according to
E 1 quation :
Eq. 1
Alternatively, the default maximum value of 750mA per
channel is used when the FRSET pin is grounded.
The flash mode current can be initiated at the preset
FRSET brightness level by asserting FEN pin high or by
setting the I2C f c r lash ontrol egister (address 01h) for the
desired f ash duration, subjected to the flash safetl y timeout
setting. The flash mode current is terminated when the
FEN pin is brought and the Ilow 2C flash register is
cleared.
Flash mode current can be to a fraction of the adjusted
maximum flash mode level (either default or set by the
FRSET resistor) by selecting the desired flash current level
percentage in the flash ontrol c register (Address 01h)
through the I2C interface. The flash current is the product
of the maximum flash current setting and the percentage
selected in the flash register.
The flash safety timeout feature automatically shuts down
the flash current if the flash mode is enabled for an
extended period of time. Refer to the lash afety imer“F S T ”
setting in Table 4.
The f nhibit (FI) pin can be used to synchronize the lash i
f plash current to a handset GSM ulse event to prevent
excessive battery droop. When FEN and FI pins are both
high, the f mode current is limited to the torch mode lash
current setting. The FI Pin is also functional when the flash
mode current is enabled through the I2C flash register.
Torch Mode
The maximum torch mode level can be adjusted through
an external resistor connecting to the TRSET pin
according to Equation 2:
TRSET
LED(MAX) 4R
7500
I=
Eq. 2
Alternatively, the default maximum value of 187.5mA per
channel is used when the TRSET pin is grounded. The
t orch mode operation is activated by asserting the TEN pin
high or by setting the I2C torch register (address 02h) for
the desired duration. The torch mode current is terminated
when the TEN pin is brought and the Ilow 2C torch register
is cleared.
Like the flash mode current, the torch mode current can be
set to a fraction of the maximum torch mode level (either
default or set by TRSET resistor) by selecting the the
desired egister torch current level percentage in the torch r
(Address 02h) through the I2C interface. The torch current
is the product of the maximum torch current setting and
the percentage selected in the torch register.
Overvoltage Protection
When the output voltage rises above the OVP thres hold,
the MIC2870 is turned off automatically to avoid
permanent damage to the IC.
Open Circuit Detection
The open-circuit detector is active only when the (OCD)
LED current regulator is turned on. When the external LED
is missing or fails open, the LED1/2 pin voltage is pulled to
near the ground potential by the internal current sink. If
both LEDs are open or mis the open circuit detector sing, -
would force the boost regulator and LED current regulator
to turn off. The MIC2870 will try to turn on the boost
regulator and LED current regulator again after a 100ms
timeout. However, in most practical cases, the boost
output voltage would rise above the OVP threshold, when
both LED channels have an open fault. The OVP function
would cause the MIC2870 to shut down.

Specyfikacje produktu

Marka: Microchip
Kategoria: nieskategoryzowany
Model: MIC2870YFT

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