1

dc1666af

DEMO MANUAL DC1666A

Description

LT3791

Four-Switch Buck-Boost

LED Driver Controller

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.

DC1666Afeaturesveryhighefficiencyat300kHzswitching

synchronousfour-switchtopologybothstepsupandsteps

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

Three sense resistors provide constant output current

control and monitoring, peak switch current control, and

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

above 57.6V, overvoltage lockout turns the switches off

below 56.2V.

DC1666A PWM dimming is simple. The PWM dimming

MOSFET turns the LED string on and off with an input to

thePWMdimmingterminal.ForthehighestPWMdimming

ratio, it is recommended to use 100Hz as a PWM dimming

frequency.InformationregardingPWMdimmingratiosand

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

L

, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.