What is the function of the Rs pin on the ADM3053?
The RS pin on the ADM3053 can be used to switch between normal high speed operation and a lower speed "slope control" mode on the CAN transceiver. The driver will have slower transitions in slope control mode to reduce EMI. The RS pin is connected directly to ground (Gnd2) for normal high-speed operation. For slope control mode, the RS pin can be connected to Gnd2 through a resistor, typically 47 kΩ.
A shielded cable is recommended for high speed operation (RS to Gnd2) to avoid EMI issues, whereas in slope control mode, the use of unshielded cable or a pair of wires is possible as EMI is reduced.
A typical plot for the ADM3053 driver slew rate versus the slope control resistor value (in kΩ) on the RS pin is shown below:
What is the expected state in case Rs input is left floated?
The RS pin on ADM3053 cannot be left floating, it must be pulled to ground (bus side) externally, either shorted for full-speed, or through a resistor (e.g. 47kΩ) for slew-rate limiting.
Left floating, there's no guarantee what operational mode the CAN transceiver will be in.
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