LTC7860/LTC7862 High-Efficiency Surge Stopper

Analog Devices' LTC7860 and LTC7862 are high-efficiency switching surge stoppers that protect loads from high voltage transients. The high-efficiency switching allows high output currents, small solution sizes, and high reliability. During an input overvoltage event, the LTC7860 controls the gate of an external MOSFET to act as a switching DC/DC regulator (PROTECTIVE PWM mode). The LTC7862 controls the gates of two external N-channel MOSFETs to act as a switching DC/DC step-down regulator. This maintains the output voltage at a safe value, allowing the loads to continue to operate through the input overvoltage event.

During normal operation (SWITCH-ON mode), the LTC7860 turns on the external MOSFET continuously, passing the input voltage through to the output. The LTC7862 turns on the top external N-channel MOSFET continuously, passing the input voltage through to the output, with minimal voltage drop. Using a fast peak current comparator, the LTC7862 also limits the maximum output current to protect against overcurrent and short-circuit faults.

An adjustable timer limits the time that the LTC7860 and 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 LTC7860 and LTC7862 restart. By strictly limiting the time in PROTECTIVE PWM mode when the power loss is high, the components and thermal design can be optimized for normal operation and safely operate through high voltage input surges and overcurrent faults. An additional PMOS can be added for reverse battery protection. The LTC7860 and LTC7862 were designed for telecom, automotive, and avionic surge protection applications.