Demonstration circuit 2560A is a 18V, 10A synchronous step-down Silent Switcher®2 with spread spectrum frequency modulation featuring the LT8642S. The demo board is designed for 1.2V output from a 2.8V to 18V input. The LT8642S is a compact, ultralow emission, high efficiency, and high speed synchronous monolithic step-down switching regulator. The integrated bypass capacitors optimize all the fast current loops and make it easier to minimize EMI/EMC emissions by reducing layout sensitivity. Selectable spread spectrum mode can further improve EMI/EMC performance. Fast minimum on-time of 20ns enables high VIN to low VOUT conversion at high frequency.
The LT8642S switching frequency can be programmed either via a resistor or external clock over a 200kHz to 3MHz range. The default frequency of demo circuit 2560A is 2MHz. The SYNC pin on the demo board is grounded (JP1 at BURST position) by default for low ripple Burst Mode® operation. To synchronize to an external clock, move JP1 to SYNC and apply the external clock to the SYNC terminal. Spread spectrum mode and forced continuous mode can be selected respectively by moving JP1 shunt.
The demo board has an EMI filter installed. This EMI filter can be included by applying the input voltage at the VIN_ EMI terminal.
The LT8642S data sheet gives a complete description of the part, operation and application information. The data sheet must be read in conjunction with this demo manual for demo circuit 2560A. The LT8643S is assembled in a 4mm × 4mm LQFN package with exposed pads for low thermal resistance. The layout recommendations for low EMI operation and maximum thermal performance are available in the data sheet section Low EMI PCB Layout and Thermal Considerations.