CAN bus must always be resistor shunted (terminated)

[zenerbjt]

Do you agree that even if you are only using a CAN bus to port a simple low frequency signal such as eg a low frequency PWM (speed control signal) being sent to an 3 phase BLDC inverter …then you still need a termination resistance shunting the CAN bus?

We are using the TCAN332 CAN transceiver.

TCAN332 CAN tranceiver

https://www.ti.com/lit/ds/symlink/t...tCh0Sbg_lEAAYASAAEgJymPD_BwE%26gclsrc%3Daw.ds

 

[rjenkinsgb]

Yes.
The driver ICs are only switches and without the terminating resistors the bus voltages will not return to the idle state quickly.
It may work without termination for short busses but could be erratic and sensitive to noise.

CAN interface ICs are specifically for the CAN network protocol and are not really suitable for other data. They may not work at all or may be erratic.

If you want a general driver/receiver system for sending such as a PWM waveform, you are far better off using RS422 or RS485 type bus interface ICs. They still need termination for anything other than short cables, but are active in both logic states rather than relying on the termination for one state.

 

[zenerbjt]

CAN interface ICs are specifically for the CAN network protocol and are not really suitable for other data. They may not work at all or may be erratic.

Thanks...i'm now getting that sinking feeling. There was an assumption that we could just send a unipolar PWM signal by shovelling it through a CAN transceiver and off we go.....so we could be making things like noise even worse now?

 

[rjenkinsgb]

Possibly. CAN is a rather weird system in some ways, it's intended to tolerate more than one device attempting to drive the bus without harm, hence the resistor to return it to the idle state rather than an active drive to both states.

The driver ICs also have some form of time limiting to prevent a faulty node from blocking the bus; an improper signal may cause the driver to disable itself.

RS-485 uses a balanced and terminated bus; the drivers are usually bidirectional with enable, similar functionality to the CAN ones you are looking at.
It may not be too much work to drop an appropriate one of those in, instead?

eg.

https://datasheets.maximintegrated.com/en/ds/MAX14775E-MAX14776E.pdf