LT8645SA

The evaluation circuit EVAL-LT8645SA-AZ is a 65V, 8A synchronous step-down second generation Silent Switcher^® with spread spectrum frequency modulation featuring the LT8645SA. The evaluation board is designed for 5V output from a 5.6V to 65V input. The wide input range allows a variety of input sources, such as automotive batteries and industrial supplies. The LT8645SA 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. Ultralow quiescent current in Burst Mode® operation achieves high efficiency at very light loads. Fast minimum on-time of 40ns enables high V_IN to low V_OUT conversion at high frequency.

The LT8645SA switching frequency can be programmed either through oscillator resistor or external clock over a 200kHz to 2.2MHz range. The default frequency of EVAL-LT8645SA-AZ 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. Select the spread spectrum mode and forced continuous mode (FCM), respectively, by moving the JP1 shunt. Figure 1 in the User Guide shows the efficiency of the circuit at 12V input and 24V input in Burst Mode operation (input from V_IN terminal to bypass the EMI filter). Figure 2 shows the LT8645SA temperature rising on EVAL-LT8645SA-AZ board under different load conditions. The rated maximum load current is 8A, while derating is necessary for certain input voltage and thermal conditions. Low switching frequency can extend the output load capability by reducing the power dissipation. Figure 3 in the User Guide shows the temperature rising at 400kHz switching frequency.

Please see the User Guide for the full description.