DESCRIPTION
Demonstration Circuit 2841A is a 42V, 15A synchronous
step-down Silent Switcher 2 with spread spectrum
frequency modulation featuring the LT8648S. 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 LT8648S is a compact, ultralow emission, high
efficiency, and high speed synchronous monolithic stepdown
switching regulator. The integrated bypass capacitors
optimize the fast current loops and make it easier to
minimize EMI emissions by reducing layout sensitivity.
Selectable spread spectrum mode further improves EMI
performance, making it perfect solution to the noise sensitive
applications.
Peak current mode control with minimum on-time of as
small as 25ns allows high step-down conversion even at
high frequency. The LT8648S switching frequency can be
programmed either via oscillator resistor or external clock
over a 200kHz to 2.2MHz range. The default frequency of
demo circuit 2841A is 400kHz.
The SYNC/MODE pin on the demo board DC2841A is
grounded (JP1 at BURST position) by default for low
ripple Burst Mode® operation. It can be configured into
different operation modes through JP1 and SYNC terminal
(Table 1).
Figure 1 shows the efficiency of the circuit at 12V input
and 24V input in force continuous mode without spread
spectrum. To get accurate efficiency measurement, measure
the input voltage at the VIN SENSE terminal and
measure the output voltage at the VO SENSE terminal.
Figure 2 shows the LT8648S temperature rising on
DC2841A demo board under different load conditions. The
LT8648S is assembled in a 7mm × 4mm LQFN package
with exposed pads for low thermal resistance. The rated
maximum load current is 15A, while derating is necessary
for certain input voltage and thermal conditions.