What this -48V hot swap controller does on a backplane
The LTC4252CCMS-1#PBF is a single-channel hot swap controller designed for -48V supply rails — the standard voltage in telecom and datacom central-office equipment. It lets you insert a line card into a live backplane without glitching the shared -48V bus or damaging the card's input capacitors. Because it has no internal switch, you pair it with an external N-channel MOSFET that handles the inrush current. The controller ramps the gate voltage to limit the surge, then holds the FET fully on once the output is stable.
Programmable protection and fault response
Four programmable features — current limit, fault timeout, overvoltage protection (OVP), and undervoltage lockout (UVLO) — let you set the safe operating window for the card. The latched fault behaviour means the controller shuts off and stays off after a fault; it does not auto-retry, so a sustained short on the card does not cause repeated power cycling. The controller itself draws 900 µA from the -48V rail, which is negligible compared to the load current the external FET switches.
Housed in a 10-lead MSOP with 0.50 mm pitch, the LTC4252CCMS-1#PBF fits a compact footprint on the line-card edge near the -48V input connector. The 10-TFSOP and 10-MSOP share the same 3.00 mm body width, so the same PCB layout accepts either package variant.