Analog Devices LT8640 | Demoboard DC2202A

Description

Demonstration circuit 2202A is a 42V, 5A micropower synchronous step-down Silent Switcher® with spread spectrum frequency modulation featuring the LT®8640. The demo board is designed for 5V output from a 5.7V to 42V input. The wide input range allows a variety of input sources, such as automotive batteries and industrial supplies. The LT8640 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. Selectable spread spectrum mode can further improve EMI/EMC performance. Ultralow 2.5μA quiescent current in Burst Mode® operation achieves high efficiency at very light loads. Fast minimum on-time of 40ns enables high VIN to low VOUT conversion at high frequency.

The LT8640 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 (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 turret. Spread spectrum mode and pulse-skipping mode can be selected respectively by moving JP1 shunt. Figure 1 shows the efficiency of the circuit at 12V and 24V input in Burst Mode operation (input from VIN turret pin). Figure 2 shows the LT8640 temperature rising on DC2202A demo board under different load conditions. The rated maximum load current is 5A, while derating is necessary for certain input voltage and thermal conditions.

The demo board has an EMI filter installed. The EMI performance of the board (with EMI filter) is shown on Figure 3. The red line in Figure 3 is CISPR25 Class 5 peak limit. The figure shows that the circuit passes the testwith 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. An inductor L2, which is a 0Ω jumper on the board by default now, can be added in the EMI filter to further reduce the conducted emission

The LT8640 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 2202A. The LT8640 is assembled in a3mm × 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 Thermal Considerations and Peak Output Current.

More information

• Datasheet
• IC product information