Analog Devices Linear ADI Power DC2686A Manual page 4

DEMO MANUAL DC2686A
BOARD OPTIONS
SETUP DIFFERENCES BETWEEN BUCK VS BUCK-MODE
When using DC2686A with a buck LED driver, connect the
V of the buck LED driver directly to V
IN
ensure that V is 6V higher than channel source voltages
IN
on the LT3967. When interfacing with a floating buck-
mode LED driver, a charge pump is necessary to create
the needed 6V headroom from V
erence LT3967 data sheet for details on how to properly
implement this.
SETTING THE ADDRESS AND POR DEFAULT
SWITCH STATE
2
Both the I C address and power-on-reset (POR) default
switch state are configured by placing resistors between
the ADDR pins. Connecting the ADDR pins either V
2
GND defines the unique I
less than 5k to set the address configures the LT3967
to start-up with the LEDs off, and using a resistor value
greater than 50k configures the LEDs to be on. Refer to
the LT3967 data sheet for detailed explanation on setting
the default POR settings and I
SETTING THE PWM DIMMING FREQUENCY
Dimming frequency for the LT3967 can be configured
either by the internal oscillator or an external clock source.
The LT3967's internal oscillator frequency is set by con-
necting a resistor from the RTSYNC pin to GND. Refer to
the LT3967 data sheet for guidance on sizing this resistor
for the desired dimming frequency.
An external clock source capable of sink 500µA at 0.4V
can be used to override the internal oscillator. If either
the internal oscillator or external clock source become
slower than 100kHz, then the IC will switch to a 100kHz
internal standby clock. The PWM dimming frequency is
derived using clock division of the RTSYNC signal, diving
down by 2048. DC2686A is equipped with an external
clock source (LTC6900CS5) that can be powered from the
5V rail of either the onboard LDO or a connected Linduino.
4
of LT3967, and
IN
to V . Please ref-
IN SRC
C address. Using a resistor value
2
C address.
UTILIZING LT3960 FOR SERIAL COMMUNICATION
The LT3960 can be used to communicate with the
LT3967 over longer distances and/or in noisy environ-
ments. DC2686A has two LT3960 ICs, one local to the
LT3967 IC, and another on a snap-off board that plugs
directly into the QuikEval header of the Linduino demo
circuit (DC2026C).
The LT3960 on the snap-off board is powered by a
Linduino when connected via QuikEval header. The EN/
MODE pin is tied to the drain of a MOSFET that can be
controlled by a Linduino. The MOSFET allows configu-
ration of IC to be set to master mode, slave, or power
off. The LT3960 on the main board can be powered by
the on-board LDO. EN/MODE pin is not connected, con-
figuring this device in slave mode. Twisted pair connec-
or
DD
tions should be made between the differential pins of the
LT3960 using the terminal blocks to connect.
PROGRAMMING THE NUMBER OF CHANNELS
A single LT3967 can control up to 8 individual chan-
nels. For any unused channels, connect the associated
DRN pins to V
DD
to GND. This ensures proper fault monitoring for the
unused channels.
LEDs can be driven in series by adding 0Ω resistors to
R6, R7, R10, R11, R12, R14, R15, which connects adja-
cent DRN and SRC channels at the J2 and J4 connectors.
Channels can also be separated for individual LEDs control
with non-serial LED string connections. DC2686A is con-
figured for 8-channel operation but has resistor options
that allow for easy reconfiguring to allow for as low as
6 LEDs. Solder a 0Ω resistor to R16, R18, and 100k to
R20, R21 to defeat the lower 2 channels of the LT3967.
CONFIGURING THE ARDUINO COM TERMINAL
For operation of the command line interface, parameters
of the terminal window must be set properly. 115200
Baud, No line ending, and Clear output should be selected.
See Figure 3 for details.
with 100k resistor and the SRC pins
Rev. 0