MIC2870 Datasheet, PDF (13/25 Pages) Micrel Semiconductor – 1.5A Synchronous Boost Flash LED Driver with I2C 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 5.0V. A 4.7µF low-ESR ceramic input capacitor
should be connected from VIN to AGND as close to
MIC2870 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 MIC2870 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.
AGND
This is the ground path for the internal biasing and control
circuitry. The current loop of the analog ground should be
separated from that of the power ground (PGND). AGND
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 and the ground path of the
LED current sinks. The current loop for the power ground
should be as small as possible and separate from the
AGND loop as applicable.
OUT
Boost converter output pin which is connected to the
anode of the LED. A low-ESR ceramic capacitor of 2.2µF
or larger should be connected from OUT to PGND as
close as possible to the MIC2870. The minimum voltage
rating of 10V is recommended for the output capacitor.
LED1/LED2
The current sink pins for the LED(s). The LED anode is
connected to the OUT pin and the LED cathode is
connected to the LED1/LED2 pin(s).
EN
This is the enable pin of the MIC2870. The MIC2870 is in
standby mode when the EN pin is asserted high. If this
pin is driven low for more than 1s, the IC is shutdown.
Alternatively, the I²C interface can be used for
enabling/disabling the IC through the master
control/status register. EN is pulled down by an internal
resistor.
MIC2870
FEN
FEN is the hardware enable pin for flash mode. A logic
low-to-high transition on FEN pin initiates the flash mode.
If FEN pin 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 control register is cleared.
TEN
TEN is the hardware enable pin for torch mode. A logic
low-to-high transition on TEN pin initiates the torch mode.
If TEN pin is left floating, it is pulled down internally by a
built-in 1µA current source when the device is enabled.
Torch mode is terminated when TEN is pulled low or left
floating, and the torch control register is cleared.
FI
FI is the flash inhibit pin. When this pin is high in flash
mode, both LED1 and LED2 currents are changed from
the flash-mode current level to the torch-mode current
level. When this pin is low, both LED1 and LED2 currents
are changed from torch-mode current level back to the
original flash-mode current level.
FRSET
The flash-mode maximum LED current level is
programmed through FRSET. A resistor connected from
FRSET to AGND sets the maximum current in the flash
mode. FRSET can be grounded for the default flash-
mode current of 0.75A. For best current accuracy, a 0.1%
tolerance resistor is recommended. FRSET cannot be left
floating and the maximum resistance is limited to 80kΩ.
TRSET
The torch-mode maximum LED current level is
programmed through TRSET. A resistor connected from
the TRSET pin to AGND sets the maximum current in the
torch mode. TRSET can be grounded for the default
torch-mode current of 187.5mA. For best current
accuracy, a 0.1% tolerance resistor is recommended.
TRSET cannot be left floating and the maximum
resistance is limited to 80kΩ.
SCL
I²C clock input pin provides a reference clock for clocking
in the data signal. This is a high-speed mode up to
3.4MHz input pin, and requires a 4.7kΩ pull-up resistor.
SDA
I²C data input/output pin allows for data to be written to
and read from the MIC2870. This is a high-speed mode
up to 3.4MHz I²C pin, and requires a 4.7kΩ pull-up
resistor.
September 5, 2013
13
Revision 1.0