Hot Swap controller for -48V telecom backplanes
The LTC4251IS6#TRMPBF is a single-channel Hot Swap Controller from Analog Devices, designed for -48V applications. It manages inrush current and provides fault protection for boards plugged into a live backplane, preventing glitches and damage on the upstream supply. Operating from a -75V to -43V supply rail, it draws only 800 µA from the bus, keeping the quiescent load negligible in a typical telecom shelf where dozens of line cards share a -48V feed.
TSOT-23-6 footprint and board integration
Housed in a 6-lead TSOT-23-6 package (SOT-23-6 Thin), the part mounts on a standard surface-mount footprint. The small outline suits dense line-card layouts where board real estate is tight, but the thermal dissipation is managed externally since the controller does not carry the load current itself — it drives an external N-channel MOSFET.
Programmable protection and fault handling
The controller integrates a programmable circuit breaker, current limit, fault timeout, overvoltage protection (OVP), and undervoltage lockout (UVLO). These are set with external resistors and capacitors, letting the board designer tune the response to match the load capacitance and the upstream breaker coordination. A latched fault response means that after a fault event (overcurrent or overvoltage), the controller shuts off the external MOSFET and stays off until the input power is cycled or the ON pin is toggled — a deliberate choice for systems where automatic retry could mask a persistent fault.