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).