The EVAL-LT3964-1-AZ evaluation circuit is a 36V synchronous dual Light-emitting diode (LED) driver with I2C featuring the LT3964-1. It drives two channels of LEDs at 1A when VIN is between 9V and 36V. EVAL-LT3964-1-AZ runs at 2MHz switching frequency. Its two channels can drive separate LED strings, which can have different currents, voltages, or dimming ratios. It can be controlled with I2C communications, or it can be run in non-I2C mode with proper ADDR pin settings. It is protected against both open and short LED conditions and reports the faults. In I2C mode, faults can be enabled or disabled. Up to 8 different EVAL-LT3964-1-AZ can be placed on the same I2C bus with unique addresses. A serial interface is available when connected to a DC2026C Linduino® One demo circuit.
The LT3964-1 has an input voltage range from 4V to 36V. It has two independent 1.8A, 40V bucks with internal, synchronous 40V switches for high efficiency and small size. It has an adjustable switching frequency between 200kHz and 2MHz. It can be synchronized to an external source or programmed with a clock output (CLKOUT). The PWMTG high-side PWM MOSFET drivers assist with short-circuit protection and versatility. Although the evaluation circuit is optimized for just two LEDs per channel, it can be altered to be buck regulators with as high as 33V of LEDs if VIN is high enough and circuit components are changed appropriately.
In non-I2C mode, each channel can separately be PWM- and analog-dimmed by placing a PWM signal or CTRL voltage on the provided turrets. In I2C mode, each channel can be dimmed to up to 8192:1, and analog dimmed to a high ratio using serial communications.
Small ceramic input and output capacitors are used to save space and cost. The open LED overvoltage protection uses the IC’s constant voltage regulation loop to regulate the output to approximately 8.1V if the LED string is opened.
Undervoltage lockout can be adjusted on the circuit with a few simple resistor choices. The output voltage (overvoltage protection) can be adjusted by changing the feedback resistors for higher string voltages. Other components may also need to be changed to accommodate higher voltages.
The LT3964-1 data sheet gives a complete description of the device, operation, and applications information. The data sheet must be read in conjunction with this user guide for EVAL-LT3964-1-AZ. The LT3964RUHE-1#PBF is assembled in a 36-lead plastic 5mm × 6mm QFN package with a thermally enhanced ground pad. A proper board layout is essential for maximum thermal performance. Refer to the datasheet Layout Considerations section.
