Hello,
Usually, we connect an external relay in this manner:
Note: if you use different power supplies for TRB245 and relay, their ground wires must be connected together.
Note: some relays have internal protection diode D. When connecting such relay you mustn’t mix up coil contacts. If you mix up the relay coil contacts you might cause permanent damage to the open collector output.
I hope it helps
Regards,
Mellow