Switching surge stopper protects against transients of over 200V

March 05, 2015 // By Graham Prophet
LTC7860 is a high-efficiency switching surge stopper with overvoltage and overcurrent protection for high availability systems.

During normal operation the LTC7860 turns on an external P-channel MOSFET continuously to pass the input voltage through to the output with minimum conduction loss. During an input overvoltage condition, the LTC7860 controls the external MOSFET to operate as a high efficiency switching DC/DC regulator to protect critical downstream components by limiting the output voltage and current.

High efficiency switching protection is extended in output current capability and reduced power loss during transients and faults. Supply voltages surge when the load current changes abruptly in long inductive power busses. The situation is aggravated in automotive applications by the energy stored in the alternator inductance, causing an elevated and extended voltage surge during a load dump. The power handling capability of a surge stopper is limited by the power lost in the protection device. In a linear surge stopper, the power capability is determined by the size of the pass MOSFET, while in a switching surge stopper the power capability is determined by conversion efficiency. Due to its lower power loss, a switching surge stopper can operate through longer input voltage surges at higher output current than a linear solution.

The LTC7860 has an input voltage operating range of 3.5V to 60V, which can be extended with external circuitry up to 200V and higher. An external fault timer capacitor configures the limited time spent in overvoltage mode and keeps the switching surge stopper below a safe peak operating temperature when power loss is at its highest levels. The fault timer reduces system cost and size by optimising component selection for normal mode rather than overvoltage transient and fault conditions.

In MIL-STD-1275 applications the LTC7860 protects devices operating from a 28V vehicle power bus which can reach as high as 100V for up to 500 msec. The LTC7860 is suitable for industrial, avionics and automotive power applications including ISO7637, as well as positive high voltage distributed power Hot Swap systems.

In a thermally enhanced 12-lead MSOP package, prices start at $2.95 (1,000). Four temperature grades are available, with operation from -40°C to 125°C for the extended and industrial grades, a high temp automotive grade of -40°C to 150°C and a military grade of -55°C to 150°C.

Linear Technology; www.linear.com/product/LTC7860

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