RS3-4812S (945-2000-5-ND) is a DC DC power supply made by Recom Power that converts 36 to 72VDC down to 12V with a maximum output of 250mA. There is also a remote on/off feature. This post aims to clarify details about the recommended circuit setup for the remote on/off features.
Remote Control is Almost Always Optional
Most DC DC converters or any kind of power supply that have a remote on/off feature is completely optional. The datasheet would typically indicate if you have to tie the control pin to ground or give specific instruction if you don’t plan to use it if the infrastructure/topology requires it.
The datasheet for this part has a diagram showing two setups on page 3.
There is a possible source of confusion here, which one do you use? Instead of being conflicting information, this is just explaining that you can incorporate remote control in two ways. The first is the recommended method of using the built in control pin with a ~68 ohm resistor and a 1N418 (or equivalent) diode with a control voltage that ranges from 5-12VDC. If no voltage (or high impedance) is applied to Vctrl, it will remain on. It will turn off if there is a voltage present.
The second method shows a way to accomplish a similar behavior without using the CTRL pin. This method appears to have a Vctrl signal, a 10k resistor, and some kind of MOSFET or similar transistor on the -Vin line. If the Vctrl voltage goes high, it would turn on, if it goes low, it would turn off. Think of this as an “inverted” operation compared to the first method.
You don’t have to incorporate the control pin though, if left open, it will still function normally.