N-channel MOSFET switch stops 150V transients

August 08, 2018 // By Nick Flaherty
Analog Devices has launched a high efficiency switching surge stopper with overvoltage and overcurrent protection for high availability systems.

The Power by Linear LTC7862 drives an N-channel power MOSFET stage. During normal operation, this passes the input voltage through to the output with minimal conduction loss. When an input overvoltage condition occurs, the device starts switching as a high efficiency DC-DC regulator, protecting downstream components by limiting the output voltage and current.

The LTC7862 builds on popular linear surge stoppers such as the LTC4363 by offering high efficiency switching protection to extend output current capability and reduce power loss during transients and faults. Supply voltages surge when the load current changes abruptly in long inductive power busses and the situation is aggravated in automotive applications by the energy stored in the alternator’s 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 circuit. 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. The lower power loss means a switching surge stopper can operate through longer input voltage surges at higher output current than a linear solution.

The LTC7862 has an input voltage operating range of 4V to 140V, 150V abs max. 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 saves system cost and size by allowing component selection to be optimized for normal mode rather than overvoltage transient and fault conditions. 

In MIL-STD-1275 applications the LTC7862 protects devices operating from a 28V vehicle power bus, where this bus voltage can reach as high as 100V and last up to 500ms. The LTC7862 also fits into industrial, avionics, and automotive power, including ISO 7637. 

The LTC7862 is available in 20-Lead 4mm × 5mm


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