QUICK START GUIDE FOR DEMONSTRATION CIRCUIT
1268A-A, 1268A-B
HIGH VOLTAGE LED CONTROLLER
4
from the PWM rising edge and the SYNC rising
edge – with the PWM edge occurring first. For more
questions regarding this matter, please consult the
factory.
Although DC1268A-A/B is assembled as a boost
topology LED driver, it can be reconfigured for
buck-boost mode, buck mode and SEPIC LED
driver topologies. A few schematics featuring these
other topologies are attached. Please keep in mind
that the chosen topology should reflect the relation-
ship between the entire input voltage range and the
LED voltage range. Other circuit requirements such
as short circuit between terminals or ground can be
affected by the choice of LED driver topology.
TERMINAL OPTIONS
DC1268A-A/B has both PVIN and VIN terminals. The
schematic shows that the PVIN and VIN terminals are
shorted together with a resistor. As assembled, only
the PVIN terminal needs 8V to 40V power in order for
the board to operate. However, resistor R2 can be re-
moved and the VIN terminal can be connected to a
separate supply from the PVIN terminal. The VIN ter-
minal is tied directly to the VIN pin.
The VOUT terminal is available for the customer to
monitor the state of the output capacitor directly. The
VOUT terminal can also be used as an input for buck
mode topology.
The PWM terminal must be pulled high in order for the
board to operate. It is preferred that the PWM termi-
nal/pin is tied to IntVcc of the controller if PWM dim-
ming is not used, but for board evaluation it can be
tied to an external 5V source as well.
The CTRL terminal is used for analog dimming. The
CTRL pin is tied directly to the terminal and it is al-
ready being used to reduce the LED current when VIN
drops too low. The CTRL pin voltage can easily be
overridden with an external voltage supply and the
resistor divider from VIN can be removed.
The shutdown/undervoltage terminal is used to shut
down the demonstration circuit. Tie the terminal to
GND and the converter will stop switching. The
PWMOUT pin will go low and the PWM dimming
MOSFET will be turned off. As long as the PWM dim-
ming MOSFET is used properly, the LEDs will not turn
on during shutdown.
