What the -48V rail and 300 ns turn-off mean for a redundant supply
The LTC4355HMS#PBF is an N+1 ORing controller designed for -48V distributed power systems and AdvancedTCA® platforms — the standard backplane voltage in telecom and central-office equipment. It drives an external N-channel MOSFET to OR two input supplies, so if one rail drops or shorts, the other holds the load without a diode drop eating into the -48V margin. The 300 ns turn-off delay means the controller reacts to a fault fast enough to prevent reverse current from the good rail bleeding into the failed one — critical in a -48V system where the load capacitance can hold several joules. The 2:1 input-to-output ratio handles two feeds, typical of a dual-feed AdvancedTCA shelf.
The 16-MSOP package (3.00 mm width, 0.118" body) is a compact footprint for a crowded backplane card; the 16-TFSOP case code is the same mechanical outline. No internal switches — the controller drives an external N-channel MOSFET, so the designer selects the FET that matches the load current and thermal budget. The 2 mA supply current is the controller's own draw; the FET gate drive comes from the -48V rail through an internal charge pump, so no separate bias supply is needed.