DC2345A: 2A @ 25V Max, 4 ~ 60V in

Demonstration circuit 2345A is a 60V synchronous 4-switch buck-boost LED controller with spread spectrum featuring the LT®8391 LED driver. It accepts an input voltage from 4V to 60V and drives a single string of LEDs up to 25V at 2A. DC2345A runs at 400kHz switching frequency without spread spectrum, but spread spectrum frequency modulation (SSFM) can be enabled with a simple jumper.SSFM spreads the switching frequency to fsw ±15% for reduced EMI.

The LT8391 has a wide input voltage range down to 4V and up to 60V. It has adjustable switching frequency between 150kHz and 600kHz. There is a simple jumper option for external frequency synchronization, spread spectrum frequency modulation, or neither.

The LT8391 can be PWM dimmed with an external PWM signal and an internally-generated PWM signal. DC2345A 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 either of its two control pins. LT8391 features both open LED and short LED (LED+ to GND) protection as well as a fault output flag.

When run with both PWM dimming and spread spectrum, the spread spectrum aligns itself with the PWM signal for flicker-free operation.

Small ceramic input and output capacitors are used to save space and cost. The board is designed with capacitors on both sides of the synchronous switches 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 29.7V if the LED string is opened although it may reach 32V peak during transient from running LEDs to open. There is a protection diode from LED+ to GND to prevent negative ringing during a short-circuit with long wires.Undervoltage lockout can be adjusted on the circuit with a few simple resistor choices.

There is an EMI filter on the input of DC2345A. This filter has a 3.2uH inductor and two 4.7?F capacitors. It is effective in reducing the conducted EMI in the AM band to pass CISPR25 class 5 regulations. When run with SSFM, DC2345A has low conducted EMI.

The LT8391 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 DC2345A. The LT8391EFE is assembled in a 28-lead plastic TSSOP (FE) package with a thermally enhanced ground pad. Proper board layout is essential for maximum thermal performance. See the data sheet section 'Layout Considerations'.