Demonstration circuit 2865A is a synchronous 4-switch buck-boost LED driver featuring the LT8393. This demonstration circuit drives a single string of LEDs up to 70V at 300mA. DC2865A runs from an input voltage of 9V to 18V as-built and is capable of 4VIN to 60VIN if UVLO is adjusted. It runs at 350kHz switching frequency and features spread spectrum modulation (SSFM) which spreads the switching frequency from fSW to fSW + 25%. Both analog and PWM dimming are featured. DC2865A features undervoltage lockout (UVLO) set at 7.9V with 1.4V hysteresis for turn-on.
The LT8393 has an adjustable switching frequency between 350kHz and 2MHz. The SYNC jumper also allows external frequency synchronization.
The LT8393 can be PWM dimmed for accurate brightness control with an external PWM signal and an internally- generated PWM signal. DC2865A 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 CTRL pin.
When run with both PWM dimming and spread spectrum, the spread spectrum aligns itself with the PWM signal for flicker-free operation.
The LT8393 features both open LED and short LED (LED+ to GND) protection as well as a fault output flag.
Small ceramic input and output capacitors save space and cost. The open LED overvoltage protection uses the IC’s constant voltage regulation loop to regulate the output to approximately 70V if the LED string is opened.
The input and output EMI filters on the demo circuit reduce the EMI of this power converter. This is intended for automotive applications where CISPR25 Class 5 standards are observed. Additionally, gate resistors and grounded shield can be added on the demo circuit for further EMI reduction if necessary. In non-automotive applications, where EMI may not be as important, the input and output filter can be removed for higher efficiency.
The UVLO voltage, LED current, output voltage range, switching frequency, brightness control, and SSFM can all be adjusted with simple modifications to the demonstration circuit.
The LT8393 data sheet gives a complete description of the device, operation and applications information. The data sheet must be read in conjunction with the demo manual for DC2865A. The LT8393JFE is assembled in a 28-lead plastic TSSOP package with a thermally enhanced GND.
