Demonstration circuit 2711A is a 42V, 1.5A synchronous step-down regulator featuring the LT8608S. The demo board is designed for 5V output from a 5.5V to 42V input. The wide input range allows a variety of input sources, such as automotive batteries and industrial supplies. The LT8608S is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator with the second-generation Silent Switcher® structure that minimizes EMI and reduces PCB layout sensitivity. LT8608S consumes only 3μA of quiescent current when output is regulated at 5V. Top and bottom power switches, compensation components and other necessary circuits are inside of the LT8608S to minimize external components and simplify design.
The SYNC pin on the demo board is grounded by default for low ripple Burst Mode® operation. Move JP1 to PULSE SKIPPING position can change the operation mode to pulse-skipping operation. Once JP1 is on SPREAD SPECTRUM position, VCC is applied to the SYNC pin for low EMI spread spectrum operation. To synchronous to an external clock, move JP1 to SYNC and apply the external clock to the SYNC turret. Figure 1 in the demo manual shows the efficiency of the circuit.
The demo board has an EMI filter installed. The radiated EMI performances of the board (with EMI filter) are shown in Figure 2 and Figure 3 in the demo manual. The red lines in Figure 2 and Figure 3 are CISPR25 Class 5 peak limit. To use the EMI filter, the input should be tied to VEMI, not VIN. An inductor L2, which is shorted on the board by default now, can be added in the EMI filter to further reduce the conducted emission.
The LT8608S data sheet gives a complete description of the part, operation and application information. The data sheet must be read in conjunction with the demo manual for DC2711A.
