The LTC4354IDDB#TRPBF from Analog Devices is a -48V source selector switch that drives an external N-channel MOSFET to replace a Schottky diode in OR-ing applications for redundant power feeds. It's designed for -48V distributed power systems and AdvancedTCA® equipment where two input sources must be combined with minimal forward drop and no reverse current flow. The part controls a 2:1 input-to-output ratio, meaning it selects between two -48V rails and passes the higher voltage to the load, blocking the lower one through the external FET.
700 ns turn-off — what it means for the -48V bus
The 700 ns delay time - OFF is the speed at which the controller can shut off the external N-channel MOSFET when it detects a reverse current condition. In a redundant -48V feed, a short on one rail must be isolated before the fault propagates to the healthy supply. That 700 ns window sets the upper bound on fault energy the MOSFET must absorb before the gate is pulled down — pick a FET with a gate charge low enough that the driver can pull it below threshold within that window. The 1.2 mA supply current is the controller's own draw, not the load current; the load passes through the external FET, so the 1.2 mA is a quiescent overhead that matters for standby efficiency in always-on telecom shelves.
Industrial temperature range and package
Rated for -40°C to 85°C operating temperature, this variant (IDDB suffix) covers the industrial range needed for outdoor telecom cabinets, base stations, and unheated equipment rooms. The 8-DFN (3x2 mm) exposed-pad package — supplier device package 8-DFN (3x2) — sits on a surface-mount footprint with a thermal pad that must be soldered to a copper plane for heat sinking. The exposed pad is the main thermal path; the DFN's small footprint suits dense line cards where board space is tight.
Sourcing and lifecycle
The LTC4354IDDB#TRPBF carries an active product status and is ROHS3 compliant. It's an in-production part from Analog Devices, available through independent distribution channels. For smaller quantities, the Cut Tape (CT) option is also listed.