N+1 ORing controller for -48V telecom and AdvancedTCA backplanes
The LTC4355IDE#PBF is an N+1 ORing controller from Analog Devices, designed to manage N-channel MOSFETs in -48V distributed power systems and AdvancedTCA® equipment. It handles a 48V or -48V supply rail and coordinates two input sources to one output, with a 300 ns turn-off delay that catches reverse-current faults before they reach the load. The controller itself draws 2 mA from the rail and does not integrate the power switch — you supply the external N-channel FETs, which keeps the heat off this 14-DFN package.
300 ns OFF delay — why it matters for the backplane
The 300 ns turn-off delay is the headline spec for this controller. When one input rail droops or shorts, the controller must open the FET before reverse current flows from the good rail into the fault. At 48V, every nanosecond of delay bleeds energy into the fault path. 300 ns is fast enough for most -48V telecom shelves; if your system demands even tighter timing, the LTC4355 family shares the same die but the package and temperature grade differ — the LTC4355HMS#PBF extends the operating range to 125°C, which matters for unventilated cabinets.