DEMO MANUAL DC1666A LT3791 Four-Switch Buck-Boost LED Driver Controller Description Demonstration circuit DC1666A is a synchronous four- LED brightness and restraining the peak switch currents switch buck-boost LED driver controller. It accepts an in order to limit inductor and switch size. UVLO turns the input voltage from 4.7V to 60V, and drives up to 25V of LEDs off when V drops below 4.7V. When input rises IN LEDs at 2A. DC1666A features both PWM and analog above 57.6V, overvoltage lockout turns the switches off dimming of the LED string. It has an OPENLED flag that to protect them and they turn back on when V drops IN indicates when the LED string has been removed and it below 56.2V. has a SHORTLED flag that indicates that the output has DC1666A PWM dimming is simple. The PWM dimming been shorted to GND. In both cases, the IC remains in MOSFET turns the LED string on and off with an input to control and well protected. the PWM dimming terminal. For the highest PWM dimming DC1666A features very high efficiency at 300kHz switching ratio, it is recommended to use 100Hz as a PWM dimming frequency and continuous conduction mode (C ). The frequency. Information regarding PWM dimming ratios and CM synchronous four-switch topology both steps up and steps performance can be found in the Applications Information down voltage while regulating up to 50W of constant LED section of the LT3791 data sheet. Analog dimming is also output current at efficiencies up to 98%. The circuit can simple with a simple voltage source on the CTRL terminal. be altered for applications requiring over 100W of LEDs. Modifications can be made to DC1666A in order to convert An optional SYNC terminal is provided for synchronizing the board to higher or lower power or from an LED driver to an external clock and CLKOUT terminal provides a to a constant voltage regulator or battery charger. Please source to sync another converter to the internal clock of consult the factory or the LT3791 data sheet for details. the LT 3791. The LT3791 data sheet gives a complete description of Three sense resistors provide constant output current the part, operation and applications information. The control and monitoring, peak switch current control, and data sheet must be read in conjunction with this demo DC input current limit and monitoring. The I and SMON manual for demonstration circuit DC1666A. The LT3791 I outputs tell the user how much current is flowing VINMON is assembled in a 38-lead plastic TSSOP package with through the output and input sense resistors. a thermally enhanced ground pad. Proper board layout Small ceramic input and output capacitors are used to is essential for maximum thermal performance. See the save space and cost. The open LED overvoltage protection Layout Considerations section in the data sheet. uses the ICs constant voltage regulation loop to limit the Design files for this circuit board are available at output to approximately 28.3V if the LED string is opened. DEMO MANUAL DC1666A p erformance s (T = 25C) A PARAMETER CONDITION VALUE (TYPICAL) Input Voltage PV Range* Operating 4.7V to 60V* IN Switching Frequency R12 = 86.6k 300kHz I CTRL = Float, 7V < PV < 57.6V 2.0A LED IN V Range R7 = 1M, R9 = 44.2k 9.5V < V < 25.5V LED LED Open LED Voltage R7 = 1M, R9 = 44.2k 28.3V Typical Efficiency Boost Region PVIN = 20V, V = 25V, I = 2A 97.5% LED LED Typical Efficiency Buck-Boost Region PVIN = 24V, V = 25V, I = 2A 96.8% LED LED Typical Efficiency Buck Region PVIN = 30V, V =25V, I = 2A 97.3% LED LED Undervoltage Lockout (Falling Turn-Off) R13 = 332k and R6 = 115k 4.7V Undervoltage Lockout (Rising Turn-On) R13 = 332k and R6 = 115k 5.7V Overvoltage Lockout (Rising Turn-Off) R11 = 54.9k, R19 = 1M 57.6V Overvoltage Lockout (Falling Turn-On) R11 = 54.9k, R19 = 1M 56.2V Peak Switch Current Limit Boost Region RS = 0.004 11A Valley Switch Current Limit Buck Region RS = 0.004 10A * The guaranteed input voltage range of the LT3791 is 4.7V to 60V. Overvoltage lockout is set externally at 57.6V on this demo circuit to protect the 60V MOSFETs M1 and M2. Overvoltage lockout is adjustable. dc1666af 2 ummary