[SOLVED] How to switch digital communication?

[brightidea]

Hello guys, I am new to this forum and this is my first post.

I am in desperate need of some advice / direction regarding a circuit design problem I am trying to overcome.

I need a mechanism, preferable a suitable IC or suggestions on a combination of transistors to allow a microprocessor to switch (make or break a connection) a digital communication line.

More specifically, a CAN-BUS line.

As you may know, the CAN lines are bi-directional. I don't see a basic NPN / PNP transistor as being suitable for this task.

My most recent attempt involved the usage of 2xSPST NC analog switch (TS3A4741). This attempt failed miserably. It would seem that that off mode of this switch, is a "high impedance state". The CAN communication signal is still passing through.

I look forward to any suggestions you may have.

TIA

 

[albert22]

Some CAN bus transceivers as the NCV7341 have an enable input that allows to disable the outputs. So there will no need for an external switch. I think that is the best solution unless you are stuck with a particular transceiver without sleep mode.

 

[brightidea]

Thank you for responding Albert.

I have mocked up a basic diagram showing what I need. The CAN transceiver is not applicable because the issue is not about controlling the flow into the MCU. I need a mechanism that will allow me to break the connection of another node from the bus.

Any thoughts?

How do I implement that switch?

 

[albert22]

This chips disable the CAN bus driver. Not the flow to the MCU. So nothing should be going to the other node when you put the transceiver into standby or sleep mode.

Here is another can bus transceiver.
https://www.ti.com/lit/ds/symlink/sn65hvd230.pdf

Unpowered Node Does Not Disturb the Bus
...
The circuit of the SN65HVD230 enters a low-current standby mode during which the driver is switched off and
the receiver remains active if a high logic level is applied to pin 8. The DSP controller reverses this low-current
standby mode when a dominant state (bus differential voltage > 900 mV typical) occurs on the bus.
The unique difference between the SN65HVD230 and the SN65HVD231 is that both the driver and the receiver
are switched off in the SN65HVD231 when a high logic level is applied to pin 8 and remain in this sleep mode
until the circuit is reactivated by a low logic level on pin 8.
...
When the driver circuit is deactivated, its outputs default to a high-impedance state.

So I still think that you dont need the external switch. The only exception could be protecting the bus from a catastrophic failure of the transceiver that could tie the bus.
Anyhow.
The switch that you selected (TS3A4741) seems suitable for your purposes because it has low on resistance (.7v) and suits current needs (100mA) and low leakage. But take care with the max voltage at the analog inputs that is only 3.6v. May be the problem that you have is that you are exceeding that with the can bus voltages.
Try to select a switch with similar Ron and imax > 70mA but more input voltage swing or even a small signal relay.
Hope that this helps.

 

[brightidea]

Albert, thank you for taking the time to help find a solution to my issue, However, you still don't understand what I am trying to do.

The way CAN transceivers work is you connect CANH and CANL to the bus and then connect TX_RX to your CAN controller. I have several controllers and transceivers in my circuit. What I am trying to do is break the physical connection of the bus to an external device on the CAN BUS, which is outside of my circuit. However, when my MCU goes off line, I need to restore that physical connection. In the real world a simple physical switch would accomplish this task , but I need a digital electronic method of accomplishing this.

I think I am going to try a small relay.

 

[albert22]

brightidea,
A relay with no doubt will work ok.
What I was trying to say is that the transceivers that I mentioned place the CANH and CANL into high impedance state thus disconnecting from the can bus. Same as physical disconnection.
If you dont have access to the transceivers or they dont have the enable/disable pin, then an external switch is the only solution.
Sorry if I still not understand your requirements. I wish you luck.

 

[brightidea]

I want to close up this thread for future searches. I ended up experimenting with a small ic/solid state relay. It seems to be working perfectly.

Thanks for your help.