High efficiency switching surge suppressors provide protection against transients of 200V and higher

     Linear Technology Corporation introduces the LTC7860, a high-efficiency switching surge suppressor with overvoltage and overcurrent protection for high-availability systems. During normal operation, the LTC7860 is continuously connected to an external P-channel MOSFET to transfer the input voltage to the output with very low conduction losses. In the event of input overvoltage, the LTC7860 protects critical downstream components by limiting output voltage and current by controlling this external MOSFET to act as a high-efficiency switching DC/DC regulator.

     The LTC7860 is based on our popular linear surge suppressors, such as the LTC4363, which provide high-efficiency switching protection to extend output current capability and reduce power loss during transients and failures. In a long inductive power bus, power supply voltage surge occurs when the load current changes suddenly. In automotive applications, the energy stored in the alternator inductors will aggravate this further and cause higher and longer lasting voltage surges during load throwing.

     The power handling capability of a surge suppressor is limited by the power loss in the protection device. In a linear surge suppressor, the power capacity is determined by the size of the transmission MOSFETs, while in a switched surge suppressor, the power capacity is determined by the conversion efficiency. Switching surge suppressors have lower power losses than linear solutions, so they can operate at longer input voltage surge times and higher output currents.

     The LTC7860 has an input voltage operating range of 3.5V to 60V and can be extended to 200V and beyond with external circuitry. An external fault timer capacitor is responsible for configuring the limited time spent in overvoltage mode and keeping the switch surge suppressor below a safe peak operating temperature when the power loss is at its highest level. The fault timer optimizes component selection for normal modes rather than overvoltage transients and failure conditions, thereby reducing system cost and size.

     In MIL-STD-1275 applications, the LTC7860 provides protection for devices operating on a 28V automotive power bus with a potential voltage of up to 100V and lasting up to 500ms. The LTC7860 is ideal for industrial, avionics and automotive power applications, including ISO7637, as well as positive and high voltage distributed power Hot Swap™ systems.

     The LTC7860 is available in a heat-resistant enhanced 12-lead MSOP package for $2.95 per tablet. The device is available in four temperature grade versions, with extended and industrial temperature grade versions operating in the temperature range from -40 °C to 125°C, high temperature automotive temperature grade versions operating in the temperature range from -40 °C to 150°C, and military temperature grade versions operating in the temperature range from -55 °C to 150°C.