DEMO MANUAL DC2575A LT8391AIFE 60V 2MHz Synchronous Buck-Boost LED Driver DESCRIPTION Demonstration circuit DC2575A is a 60V 2MHz synchro- Small ceramic input and output capacitors are used to nous buck-boost LED driver featuring the LT8391A. It save space and cost. The board is designed with capaci- accepts an input voltage from 4V to 60V and drives a tors on both sides of the synchronous switches for a single string of LEDs up to 16V at 1.5A. DC2575A runs at reduction in radiated EMI. The open LED overvoltage 2MHz switching frequency without spread spectrum, but protection uses the ICs constant voltage regulation loop spread spectrum frequency modulation (SSFM) can be to regulate the output to approximately 18V if the LED + enabled with a simple jumper. SSFM spreads the switch- string is opened. There is a protection diode from LED ing frequency from f to f +25% for reduced EMI. to GND to prevent negative ringing during a short-circuit SW SW with long wires. DC2575A uses AEC-Q automotive-approved components such as power MOSFETs, diodes, input and output capaci- Undervoltage lockout can be adjusted on the circuit with tors and inductors. a few simple resistor choices. The LT8391A has a wide input voltage range down to EMI filters and gate resistors on the demo circuit reduce 4V and up to 60V. It has adjustable switching frequency this high power converters EMI below CISPR 25 Class 5 between 600kHz and 2MHz. There is a simple jumper limits. This is intended for automotive applications where option for external frequency synchronization, spread CISPR 25 EMI standards are observed. In non-automotive spectrum frequency modulation, or neither. applications, the EMI may not be as important and the input and output filters, as well as the gate resistors can The LT8391A can be PWM dimmed with an external PWM be removed for higher efficiency. Please note the optional signal and an internally-generated PWM signal. DC2575A EMI components in the parts list. SSFM is also used to has a jumper that can be set to switch between internally- reduce EMI and is not necessary in applications where generated PWM signal, externally-generated PWM signal, EMI is not important. and no PWM signal (100% on). It can be analog dimmed with a control voltage on either of its two control pins. The LT8391A data sheet gives a complete description of + LT8391A features both open LED and short LED (LED to the part, operation and applications information. The data GND) protection as well as a fault output flag. sheet must be read in conjunction with this Demo Manual for demonstration circuit DC2575A. The LT8391AIFE is When run with both PWM dimming and spread spectrum, assembled in a 28-lead plastic TSSOP (FE) package with the spread spectrum aligns itself with the PWM signal for a thermally-enhanced ground pad. Proper board layout flicker-free operation. is essential for maximum thermal performance. See the data sheet sectionLayout Consideration. Design files for this circuit board are available at DEMO MANUAL DC2575A QUICK START PROCEDURE Table 1. Typical Performance Summary for DC2575A LT8391A PARAMETER CONDITIONS MIN TYP MAX Input Voltage PV Range Operating V 16V 4V 60V IN LED Switching Frequency (f ) R3 = 59.0k, JP1 = NO SSFM/SYNC 2.0MHz SW Spread Spectrum (SSFM) Frequency Range JP1 = SSFM ON f f 1.25 SW SW I R2 = 0.056 7.0V < PV < 60V V 16V 1.5A LED IN LED R9 = 90.9k, R10 = 113k V range R5 = 1M, R6 = 54.9k 4.8V 16V LED Open LED Voltage V R5 = 1M, R6 = 54.9k 18.2V OUT Typical Efficiency (100% PWM DC) PV = 13V, V = 16V, I = 1.5A 92% IN LED LED Internally-Generated PWM Dimming Range JP2 = INT, JP3 = INT 1/128 100% Internally-Generated PWM Dimming Frequency JP2 = INT, JP3 = INT R30 = 301k, R3 = 59.0k 488Hz Peak Switch Current Limit Boost Region R1 = 0.006 8.3A Peak Switch Current Limit Buck Region R1 = 0.006 8.3A PV Undervoltage Lockout (UVLO) falling R7 = 383k, R8 = 165k 4.3V IN PV Enable Turn-On (EN) Rising R7 = 383k, R8 = 165k 5.1V IN Demonstration circuit 2575A is easy to set up to evaluate 7. Observe the LED string running at the programmed the performance of the LT8391A follow the procedure: LED current. 1. With power off, connect a string of LEDs that will run 8. To change the brightness with analog dimming, sim- with forward voltage less than or equal to 16V (at ply attach a voltage source to either the CTRL1 or + 1.5A) to the LED and LED banana jacks on the PCB CTRL2 terminal and set the voltage between 0V and as shown in Figure 1. 1.5V. See data sheet for details. 2. Connect the EN/UVLO terminal to GND. 9. To change brightness with external PWM dimming, set JP2 to EXT/ON and JP3 to EXT. Attach a 3V rect- 3. Set JP2 to EXT/ON and JP3 to ON for 100% always- angular waveform with varying duty cycle to the PWM on LED operation. Set JP1 to NO SSFM/SYNC to run terminal. without SSFM. 10. To change brightness with internally-generated PWM 4. With power off, connect the input power supply to the dimming, set JP2 to INT and JP3 to INT. Adjust the PV and GND banana jacks. Make sure that the DC IN setting of the VR1 variable resistor with a small flat- input voltage will not exceed 60V. head screwdriver to toggle between 0% and 100% 5. Turn the input power supply on and make sure the PWM dimming duty cycle in 1/128 steps. voltage is between 4V and 60V for proper operation. 11. To enable spread spectrum frequency modulation, set 6. Release the EN/UVLO-to-GND connection. JP1 to SSFM ON. dc2575af 2