DC2019B: 5V @ 4A, 5.8 ~ 42V in

Demonstration circuit 2019B is a 42V, 4A micropower synchronous step-down Silent Switcher™ featuring the LT®8614. The demo board is designed for 5V output from a 5.8V to 42V input. The wide input range allows a variety of input sources, such as automotive batteries and industrial supplies. The LT8614 is a compact, ultralow emission, high efficiency and high speed synchronous monolithic step-down switching regulator. The integrated power switches and inclusion of all necessary circuitry reduce the components count and solution size. Special Silent Switcher architecture minimizes EMI/EMC emissions. Ultralow 2.5μA quiescent current in Burst Mode® operation achieves high efficiency at very light loads. Fast minimum on-time of 30ns enables high VIN to low VOUT conversion at high frequency.

The LT8614 switching frequency can be programmed either via oscillator resistor or external clock over a 200kHz to 3MHz range. The SYNC pin on the demo board is grounded 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 turret. Once JP1 is on SYNC position, a DC voltage of higher than 3V can be applied to the SYNC turret for pulse-skipping operation.

Figure 1 shows the efficiency of the circuit at 12V input in Burst Mode operation (input from VIN turret pin). Figure 2 shows the LT8614 temperature rising on DC2019B demo board under different load conditions. The rated maximum load current is 4A, while derating is necessary for certain VIN and thermal conditions.

The demo board has an EMI filter installed. The EMI performance of the board (with EMI filter) is shown in Figure 3. The red line in Figure 3 is CISPR25 Class 5 peak limit. The figure shows that the circuit passes the test with a wide margin. To achieve EMI/EMC performance as shown in Figure 3, the input EMI filter is required and the input voltage should be applied at VEMI turret pin.

The LT8614 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 2019B. The LT8614 is assembled in a 3mm × 4mm plastic QFN package with exposed pads for low thermal resistance. Proper board layout is essential for both low EMI operation and maximum thermal performance. See the data sheet sections, “Low EMI PCB Layout” and “High Temperature Considerations.”