Linear's LT3791 is a synchronous four-switch boost-buck LED drive controller that can make VIN higher, lower or equal to VOUT, with efficiencies as high as 98.5%, input voltage 4.7V ~ 60V, output voltage 0V ~ 60V, LED Current accuracy ± 6%, true color PWM and analog dimming, each IC input power is 100W or greater than 100W. Mainly used for car headlights / travel lights and general lighting.
Its continuous constant frequency and forced constant current mode architecture make it possible to adjust or synchronize the frequency from 200kHz to 700kHz. The top MOSFET switching cycle is not required during buck or boost operation. The device is 60V input, 60V output. The seamless conversion between the work area and the work area makes the LT3791 an ideal choice for LED drivers in automotive, industrial, and battery-powered systems.
LT3791 has input current monitor, LED current monitor, and LED open or short circuit protection when restarting or blocking.
Figure 1 LT3791 block diagram
Main features of LT3791
• 4-switch single-inductor architecture allows VIN to be above, below or equal to VOUT
• Synchronous switching: efficiency up to 98.5%
• Wide VIN range of 4.7V ~ 60V:
• Wide VOUT range: 0V ~ 60V (52V LED)
• ± 6% LED current accuracy: 0V≤VLED <52V
• True Color PWM and analog dimming
• LED current monitor output and input current regulation
• No Top MOSFET refresh during buck or boost
• During shutdown, VOUT is disconnected from VIN
• Open circuit or short circuit LED fault protection
• 100W or higher per IC
• 38-pin TSSOP with exposed pad
LT3791 application
• Car headlights / traffic lights
• General lighting
Figure 2 LT3791 efficiency 98% 50W (25V2A) buck-boost LED driver circuit diagram
Figure 3 LT3791 efficiency 98.5% 100W (33.3V3A) buck-boost LED driver circuit diagram
Figure 4 DC1666A demo board circuit diagram
Demo board DC1666A
The DC1666A demonstration circuit is a synchronous four-switch buck-boost LED driver controller. Its input voltage is 4.7V ~ 60V, and it can drive up to 2A and 25V LED. DC1666A has the function of PWM and analog dimming of LED string. When the LED string is moved, its OPENLED logo displays; when the output is shorted to GND, its SHORTLED logo displays. In both cases, the IC remains in control and has good protection.
DC1666A has very high efficiency, its switching frequency is 300kHz, and has a continuous conduction mode (CCM). Its synchronous four-switch topology has an efficiency of up to 98% when regulating 50W constant LED output current (boost and buck). The circuit can be varied for LED applications over 100W. An optional SYNC terminal is used to synchronize an external clock and CLKOUT terminal, and provides another converter and internal clock (LT3791) synchronization resources. Three detection resistors provide constant output current control and monitoring, peak switch current control, and DC input current limit and monitoring. Its ISMON and IVINMON outputs can tell users how much current flows through the output and input sense resistors. Small ceramic input and output capacitors to save space and cost. LED open circuit overvoltage protection uses an IC constant voltage regulation loop to limit the output (approximately 28.3V, if the LED string is turned on). For low input voltage operation, when the input voltage is lower than 6.5V, the CTRL pin voltage is reduced, and reduces the brightness of the LED and limits the peak switch current to limit the size of the inductor and switch. When VIN drops below 4.7V, UVLO turns off the LED. When the input rises above 57.6V, the overvoltage lockout function protects the switch off, and when VIN drops to 56.2V, it turns on again.
DC1666A PWM dimming is very simple. The PWM dimming MOSFET uses the input of the PWM dimming terminal to turn on and off the LED string. For the highest PWM dimming ratio, it is recommended to use 100Hz as the PWM dimming frequency. For information on PWM dimming ratio and performance, see the LT3791 data sheet in the Application Information section. Analog dimming is also very simple, using a simple CTRL terminal voltage source.
DC1666A can be modified to convert the board to higher or lower power, or to use an LED driver to a constant voltage regulator or battery charger.
The LT3791 data sheet gives a complete description of the operation and application information. The data sheet must be read with the user manual to understand the DC1666A circuit. The LT3791 is assembled in a 38-lead plastic TSSOP package with a heat-resistant reinforced floor mat. Correct circuit board layout is essential for thermal performance.
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