LT8645S is an 8-A, 65-V input-capable
synchronous step-down switching regulator. It features the Silent Switcher
2 architecture, uses two internal input capacitors as well as internal
BST and INTVCC capacitors to minimize the area of the hot loops.
Combined with controlled switching edges and internal construction with an
integral ground plane and the use of copper pillars in lieu of bond wires, the step-down
regulator reduces EMI/EMC emissions. The improved EMI/EMC performance is not
sensitive to board layout, simplifies design and reduces risk even when using
two layer PC boards. The LT8645S can pass the automotive CISPR25, Class 5 peak
EMI limits with a 2 MHz switching frequency over its entire load range. Spread
spectrum frequency modulation is also available to lower EMI/EMC levels


LTC_LT8645S Silent Switcher _apr2017


regulator’s synchronous rectification delivers efficiency as high as 94% and
the input voltage range targets dual cell transportation, and 48 V automotive
and industrial applications. The internal high efficiency switches can deliver
up to 8 A continuous output current to voltages as low as 0.97 V. The regulator’s
Burst Mode operation offers 2.5 µA of quiescent current, suitable for automotive/
transportation always-on systems, which need to extend operating battery life.

regulator maintains a minimum dropout voltage of only 60 mV (at1 A) under all
conditions, enabling it to excel in scenarios such as automotive cold-crank.
Furthermore, a fast minimum on-time of only 40 ns enables 2 MHz constant
frequency switching from a 24-V input to a 2.0 V output, enabling designers to
optimize efficiency while avoiding critical noise-sensitive frequency bands.
The 32-lead, 4 x 6 mm LQFN package and high switching frequency keeps external
inductors and capacitors small.

The LT8645S uses internal top and
bottom high efficiency power switches with the necessary boost diode,
oscillator, control and logic circuitry integrated into a single die. Low
ripple Burst Mode operation maintains high efficiency at low output currents
while keeping output ripple below 10 mVP-P. For applications
requiring the lowest noise operation, the LT8645S can be programmed to run in
pulse-skipping mode. Its switching frequency is programmable and synchronizable
from 200 kHz to 2.2 MHz. For more information on the Analog Devices/Linear