Demonstration circuit 2674A is a 140V high efficiency
switching surge stopper featuring the LTC7862. The
board operates from an input voltage range of 8V to
140V, and provides a 8V to 34V output from 0A to 10A.
Its output voltage is programmed to be clamped at 34V
(typical) with a minimum ride-through duration of 500ms
to allow the load to operate through the input overvoltage
events. Its output current is limited to protect against
output short-circuit faults. A soft-start feature is utilized
to control its output voltage slew rate at start-up and input
voltage transients. This feature reduces current surge and
output voltage overshoot. The demonstration board is
able to achieve low insertion drop (210mV typical) by
utilizing the low RDS(ON) N-channel MOSFETs and low
DCR inductor. This board also includes optional reverse
polarity protection circuit which protects the downstream
loads up to −40V. The demonstration circuit is suitable
for a wide range of automotive, industrial, and telecom
applications.
The LTC7862 high efficiency switching surge stopper
protects loads from input high voltage transients. During
an input overvoltage event, the LTC7862 controls the
gate of two external N-channel MOSFETs and operate as
a switching DC/DC step-down regulator. The output voltage
is maintained at a safe level, allowing the loads to
continue to operate through the input overvoltage events.
During normal operation, the LTC7862 turns on the top
external N-channel MOSFET continuously, passing the
input voltage through to the output with minimal voltage
drop. The LTC7862 also limits the maximum output current
to protect against overcurrent and short-circuit faults.
A programmable timer limits the time that the LTC7862
can spend switching during an overvoltage, overcurrent,
or startup condition. When the timer expires, the external
MOSFETs are turned off for a cooldown period and
then the LTC7862 restarts. The timer limits how long the
LTC7862 can switch when the power loss is relatively
high, the components and thermal design can be optimized
for normal pass-through operation.
The LTC7862 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 DC2674A. Proper board layout is essential
for maximum thermal and electrical performance. See the
data sheet sections for details. The LTC7862 is available
in 20-lead TSSOP and QFN packages and two operating
junction temperature grades: industrial (−40°C to 125°C)
and high temperature automotive (−40°C to 150°C).
