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I am currently designing a CAN system for a 3.3 V board and I am looking for some insight regarding CAN transceivers. These are my goals from the CAN system:

  1. No influence on the CAN bus if in read-only mode.
  2. Terminating resistor - a unit may sometimes need a terminating resistor. Is there a method to overcome that?
  3. Voltage - there are not too many 3.3 V operated CAN transceivers. Is it worthwhile to look for one to save a regulator or is the special transceiver with higher cost and performance worth it?
  4. Security - the system is installed in a car. The main importance is that the system will do no harm either in receive-only mode and in trasmit mode.

What should I look for in the datasheet to accomplish these goals? Are there special methods I should look for and read about?

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  • \$\begingroup\$ Hi, I rewrote the question to talk about the methods to overcome the problems instead of looking for a component. i believe the solution can benefit anyone looking to build a CAN system. please consider reopening the question \$\endgroup\$
    – Charls Diven
    Commented Oct 14, 2013 at 11:21
  • \$\begingroup\$ CAN_H dominate calls for 3.5V \$\endgroup\$
    – user16222
    Commented Jan 19, 2014 at 10:32

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No influence on the CAN bus if in read-only mode.

The CAN controller which is (should be) integrated in your MCU most likely has a listen-only mode. When you set the controller in this mode, it will not ACK frames.

Terminating resistor - a unit may sometimes need a terminating resistor. Is there a method to overcome that?

The most convenient way is to put one such 120 ohm resistor on your board, in series with a jumper or similar, so that when the jumper is present, the resistor is connected between CAN Hi and Lo.

Voltage - there are not too many 3.3 V operated CAN transceivers. Is it worthwhile to look for one to save a regulator or is the special transceiver with higher cost and performance worth it?

I don't think 3.3V transceivers are more expensive. As usual, the price depends more on which brand and which supplier you specify, rather than the details of the actual IC. Though of course, if you specify some 48 pin QFN monster, it is going to cost you... I'm using TI's HVD232 which is small and affordable.

Security - the system is installed in a car. The main importance is that the system will do no harm either in receive-only mode and in trasmit mode.

This is all on the application level. There are many things to consider. For example, what happens if your MCU flips out in the middle of a CAN transmission, will it sink the whole bus or leave it gracefully?

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Unless you're building a CAN sniffer/snooper that only listens, there isn't really a "read-only mode". All other nodes on the CAN network simultaneously provide ACKs, check for collisions, and message validity. If you use a commercial CAN transceiver/controller combo there isn't much to worry about.

As far as termination goes, you should either know if you need a terminator or not; if you're tapping into an existing network then probably not. The cheap-but-hard-to-configure-on-the-fly method is to put a part on your board and populate it as needed. If the user needs to configure it, either add a switch (costly) or provide a separate resistor with an appropriate connector (also costly, unless you leave it up to them to source it/include it in their harness)

Some CAN transceivers are designed to be powered directly from the car's electrical system (e.g. Freescale, some of which also include an embedded regulator to power a microcontroller), others have other features...the combinations are too numerous to list. I would just look at offerings from several companies (TI, Microchip, Freescale, and literally every other semiconductor manufacturer, just click "Automotive" on their homepage) and find one that fits your criteria. Better yet, ask your supplier's applications engineer.

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  • \$\begingroup\$ That is not entirely correct. there are modes e.g. listen mode that only listen to the bus and does not interact. Also, although a transciever should have a very high impedance it is sometimes not enough, especialy when tapping to an existing system. i hoped to hear more on technology techniques and limitations regarding these problems i mentioned. Thanks for the reply though \$\endgroup\$
    – Charls Diven
    Commented Oct 15, 2013 at 8:37
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In regards to the terminating resistor, you will need it at the end of the bus to balance the impedance, but in my experience if the speed of the network is not too high (I've used it at 125kb/s), it works without the resistors. Also, apart from the 120 ohm resistor (standard termination), there is another method that improves EMC called split termination (the one I use), that involves two 60 ohm resistors and a capacitor: http://digital.ni.com/public.nsf/allkb/C03609ECFF16A14E86256E5A008293EA

I recommend also reading this application note on 3.3V CAN transceivers from TI: http://www.ti.com/lit/an/slla337/slla337.pdf

Finally, for ESD protection I use this CAN bus protection diode from NXP: http://www.nxp.com/products/automotive/discretes/esd_protection/PESD1CAN.html

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