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Diode-OR controller has lower loss than Schottky diodes

Posted: 30 Aug 2007 ?? ?Print Version ?Bookmark and Share

Keywords:Schottky OR-ing diodes? power supply? voltage diode?

The LTC4357 from Linear Technology Corp. is a single high-voltage ideal diode-OR controller that offers a simple, low-loss replacement to the Schottky OR-ing diodes in multiple, N+1 redundant, power supply applications and high availability systems.

The new device controls an external n-channel MOSFET to perform the function of a low-forward voltage diode. This provides a lower loss path compared to the Schottky diode. In high-power applications, it not only provides a more efficient solution but also preserves board area by eliminating the need for heat sinking. The LTC4357 controls the forward voltage drop across the MOSFET to ensure smooth switchover from one path to another without oscillation or reverse DC current.

The LTC4357 single diode-OR can be used in applications where multiple power supplies are paralleled to provide load-sharing. In N+1 redundant systems, an additional supply is added to safeguard the system in the event one of the N supplies fail. It is necessary to OR the supplies together to provide isolation for live insertion and removal of converters onto the power bus and to provide isolation from the bus during a hard short. If the power source fails or is shorted, the LTC4357 ensures a fast 0.5?s turn-off to minimize reverse current transients.

The LTC4357 can also be used to safeguard against reverse voltage events, providing reverse input protection to downstream electronics. Additionally, it can be configured with a Hot Swap controller and hold-up capacitor to provide input supply hold-up for a period of time after a loss of input power. This enables continuing system operation without resetting or rebooting due to brief interruptions of input power.

The wide operating range of 9-80V supports diode-OR applications with two positive supplies such as a 12V distributed bus architecture or the return paths of two negative supplies such as in -48V AdvancedTCA (ATCA) applications. The LTC4357 tolerates fast dV/dt transients during insertion, providing immunity to latchup.

Specified over the commercial and industrial temperature ranges, the LTC4357 is offered in 2mm x 3mm 6-lead DFN and 8-lead MSOP packages. Available today, pricing begins at $1.70 each in 1,000-piece quantities.

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