Description
Demonstration circuit 2373A is a 65V, 3.5A micropower
synchronous step-down Silent Switcher® with spread
spectrum frequency modulation featuring the LT®8641.
The demo board is designed for 5V output from a 5.5V to
65V input. The wide input range allows a variety of input
sources, such as automotive batteries and industrial supplies.
The LT8641 is a compact, ultralow emission, high
efficiency, high speed synchronous monolithic step-down
switching regulator that consumes only 2.5μA of quiescent
current when output is regulated at 5V. Top and bottom
power switches, compensation components and other
necessary circuits are inside of the LT8641 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 shows the efficiency of
the circuit at 12V and 24V input in Burst Mode® operation
(input from VIN turret pin). Figure 2 shows the LT8641
temperature rising on DC2373A demo board under different
load conditions. The rated maximum load current is
3.5A, while derating is necessary for certain input voltage
and thermal conditions.
The demo board has an EMI filter installed. Under burst
and spread spectrum operation, the EMI performances of
the board (with EMI filter) are shown in Figure 3 and 4. The
red lines in Figure 3 and 4 are CISPR25 Class5 peak limit.
To achieve EMI/EMC performance as shown in Figure 3
and 4, the input EMI filter is required and the input voltage
should be applied at VEMI turret pin.
This board is suitable for a wide range of automotive,
telecom, industrial, and other applications.
The LT8641 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 DC2373A.