Analog Devices LT3932 | Demoboard DC2286A

Description

Demonstration circuit DC2286A is a 36V, 2A synchronous 2MHz buck LED driver featuring the LT®3932. It drives one or two series LEDs at 1A when VIN is between 9Vand 36V, and can run down to 4VIN with a single LED (if UVLO is adjusted). DC2286A runs at 2MHz switching frequency. Spread spectrum frequency modulation (SSFM) can be enabled with a simple jumper, reducing EMI. DC2286A comes with low EMI features including optimized layout, SSFM, and input and output filters. It passes CISPR 25 class 5 conducted and radiated EMI. It is protected against both open and short LED conditions and reports the faults. The LT3932 has an input voltage range from 9V to 36V. It has 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 SSFM for low EMI. The PWMTG high-side PWM MOSFET driver assists with short-circuit protection and versatility. Although the demo circuit is optimized for one or two LEDs, it can be altered to have as high as 33V of LEDs if VIN is high-enough and circuit components are changed appropriately. The LT3932 can be PWM dimmed with an external PWM signal or an internally-generated PWM signal. DC2286A has a jumper that can be set to switch between internally-generated PWM signal, externally-generated PWM signal, and no PWM signal (100% on). It can be analog dimmed with a control voltage on its control pin. When run with both PWM dimming and spread spectrum, the spread spectrum aligns itself with the PWM signal for flicker-free operation. All registered trademarks and trademarks are the property of their respective owners. Small ceramic input and output capacitors are used to save space and cost. The board is designed with tiny, high frequency capacitors on both sides of the VOUT pins for a reduction in radiated EMI. The open LED overvoltage protection uses the IC’s constant voltage regulation loop to regulate the output to approximately 7V if the LED string is opened. There is a protection diode from LED+ to GND to prevent negative ringing during a short-circuit. The output current can be monitored through the ISMON output pin. Undervoltage lockout can be adjusted on the circuit with a few simple resistor choices. There is an EMI filter on the input of DC2286A. There is also a small ferrite bead output filter. These filters, combined with proper board layout and SSFM are effective to help the PCB pass CISPR 25 class 5 conducted and radiated EMI. Please follow the recommend layout and four-layer thickness of DC2286A for low EMI applications. The LT3932 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 DC2286A. The LT3932EUFD is assembled in a 28-lead plastic 4mm × 5mm QFN package with a thermally enhanced ground pad. Proper board layout is essential for maximum thermal performance. See the data sheet section "Layout Considerations".

More information

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