DC1666A Datasheet, PDF (1/8 Pages) Linear Technology – Four-Switch Buck-Boost LED Driver Controller

DEMO MANUAL DC1666A
LT3791
Four-Switch Buck-Boost
LED Driver Controller
Description
Demonstration circuit DC1666A is a synchronous four-
switch buck-boost LED driver controller. It accepts an
input voltage from 4.7V to 60V, and drives up to 25V of
LEDs at 2A. DC1666A features both PWM and analog
dimming of the LED string. It has an OPENLED flag that
indicates when the LED string has been removed and it
has a SHORTLED flag that indicates that the output has
been shorted to GND. In both cases, the IC remains in
control and well protected.
DC1666A features very high efficiency at 300kHz switching
frequency and continuous conduction mode (C_CM). The
synchronous four-switch topology both steps up and steps
down voltage while regulating up to 50W of constant LED
output current at efficiencies up to 98%. The circuit can
be altered for applications requiring over 100W of LEDs.
An optional SYNC terminal is provided for synchronizing
to an external clock and CLKOUT terminal provides a
source to sync another converter to the internal clock of
the LT^®3791.
Three sense resistors provide constant output current
control and monitoring, peak switch current control, and
DC input current limit and monitoring. The I_SMON and
I_VINMON outputs tell the user how much current is flowing
through the output and input sense resistors.
Small ceramic input and output capacitors are used to
save space and cost. The open LED overvoltage protection
uses the ICs constant voltage regulation loop to limit the
output to approximately 28.3V if the LED string is opened.
For low input voltage operation, the CTRL pin voltage is
reduced as the input voltage drops below 6.5V, reducing
LED brightness and restraining the peak switch currents
in order to limit inductor and switch size. UVLO turns the
LEDs off when V_IN drops below 4.7V. When input rises
above 57.6V, overvoltage lockout turns the switches off
to protect them and they turn back on when V_IN drops
below 56.2V.
DC1666A PWM dimming is simple. The PWM dimming
MOSFET turns the LED string on and off with an input to
the PWM dimming terminal. For the highest PWM dimming
ratio, it is recommended to use 100Hz as a PWM dimming
frequency. Information regarding PWM dimming ratios and
performance can be found in the Applications Information
section of the LT3791 data sheet. Analog dimming is also
simple with a simple voltage source on the CTRL terminal.
Modifications can be made to DC1666A in order to convert
the board to higher or lower power or from an LED driver
to a constant voltage regulator or battery charger. Please
consult the factory or the LT3791 data sheet for details.
The LT3791 data sheet gives a complete description of
the part, operation and applications information. The
data sheet must be read in conjunction with this demo
manual for demonstration circuit DC1666A. The LT3791
is assembled in a 38-lead plastic TSSOP package with
a thermally enhanced ground pad. Proper board layout
is essential for maximum thermal performance. See the
Layout Considerations section in the data sheet.
Design files for this circuit board are available at
http://www.linear.com/demo
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