The single bidirectional channel handles both positive and negative transients, so you place one device across the rail rather than two back-to-back Zeners.
Clamping voltage and the headroom decision
The 64.5 V clamp at 9.7 A peak pulse current sets the let-through voltage that the downstream circuitry must survive. If your rail is 48 V nominal, the 16.5 V headroom between rail and clamp is tight for a 60 V-rated downstream FET — you'll want to verify the FET's avalanche capability or step to a higher-voltage device. On a 36 V rail the margin improves, and a 60 V-rated component has comfortable room.
Rated for junction temperature from -55°C to 150°C, the SMBJ40CA-TR covers the full industrial temperature band and extends into automotive under-hood zones without derating. The DO-214AA (SMB) surface-mount package keeps the footprint small — about the size of a 1206 resistor — and the MSL rating is typically Level 1, meaning no bake required before reflow if stored dry.