Electronics > Projects, Designs, and Technical Stuff
CAN Tranceiver 3.3V
lollandster:
--- Quote from: SparkyFX on June 06, 2019, 08:42:46 pm ---The transceiver needs to be able to drive the bus dominant state to have a difference between lines of 0V - against all other recessive nodes (which output a 2.5V, high impedance, difference) and with adequate slew rate, low ringing/overshoot. In recessive state the transceiver just needs to keep the voltage level in presence of the termination resistors.
The thing is you layout the network, not just one node, to operate to certain limits (within its baudrate, wire length).
--- End quote ---
Are you guys deliberately trying to confuse me by making it sound more complicated than it is?
I found application note from TI (http://www.ti.com/lit/an/slla337/slla337.pdf) that agrees with Linear Technology. I'll quote:
--- Quote from: http://www.ti.com/lit/an/slla337/slla337.pdf ---3 CONFORMANCE TESTING
The TI SN65HVD23x 3.3V CAN families have been successfully tested by the internationally recognized third party communications and systems (C&S) group GmbH to the GIFT/ICT CAN High-Speed Transceiver Conformance Test. This testing covers a homogeneous network of all 3.3V transceivers and a heterogeneous network where four out of sixteen CAN nodes are the 3.3V transceiver and the remaining twelve CAN nodes are a mix of three other “golden” reference, non TI 5V CAN transceivers. Both TI 3.3V CAN transceiver families successfully passed this testing with no findings and the certificates of authentication were issued.
--- End quote ---
--- Quote from: http://www.ti.com/lit/an/slla337/slla337.pdf ---5 SUMMARY
3.3V and 5V CAN transceivers are interoperable because High Speed CAN physical layer uses differential signalling that is the same for a 3.3V and 5V CAN transceiver. In addition both the 3.3V and 5V CAN transceivers have the same wide common mode range accommodating not only the typical signalling but also providing wide margin for ground shift potential. For systems that can benefit from the advantages of 3.3V transceivers, such as simplified power supplies and lower power consumption they offer clear advantages in their use either in a homogeneous 3.3V CAN network or in a mixed 3.3V and 5V CAN network.
--- End quote ---
EDIT: The data logger is black box, so unless I put a probe to it, I don't know much about it. It's a HBM Quantum MX840.
Yansi:
I am sorry if my response was confusing to you. But I have clearly stated I think, that the transceiver gives zero f*cks whether the rest of the network uses transceivers powered from 5 or 3V, as long as the input signal will be within its common mode voltage limits, which are as I have stated always wider than the supply voltage.
lollandster:
--- Quote from: Yansi on June 06, 2019, 09:06:07 pm ---I am sorry if my response was confusing to you. But I have clearly stated I think, that the transceiver gives zero f*cks whether the rest of the network uses transceivers powered from 5 or 3V, as long as the input signal will be within its common mode voltage limits, which are as I have stated always wider than the supply voltage.
--- End quote ---
Yes, your explanation was clear and agreed with what I read (which is why I pressed the thanks button). What confuses me is that your peers don't agree. Since I don't know your backgrounds I don't know who to trust.
I will now stop being confused and trust TI and LT/analog (and by extension you). Thanks.
SparkyFX:
--- Quote from: lollandster on June 06, 2019, 08:59:45 pm ---Are you guys deliberately trying to confuse me by making it sound more complicated than it is?
--- End quote ---
I wish there was a simpler way to express it, but with CAN or differential signaling, forget the concept of low = 0 and high = 1.
Any node can be master, so any other node needs to be able to override (e.g. during message id transmission or during ACK), hence this is better called dominant/recessive state. Which brings the electrical characteristics into focus.
lollandster:
--- Quote from: SparkyFX on June 07, 2019, 05:51:53 pm ---
--- Quote from: lollandster on June 06, 2019, 08:59:45 pm ---Are you guys deliberately trying to confuse me by making it sound more complicated than it is?
--- End quote ---
I wish there was a simpler way to express it, but with CAN or differential signaling, forget the concept of low = 0 and high = 1.
Any node can be master, so any other node needs to be able to override (e.g. during message id transmission or during ACK), hence this is better called dominant/recessive state. Which brings the electrical characteristics into focus.
--- End quote ---
Yes, I know all the basics about how this stuff works and I know that all this stuff gets complicated fast). What I mean you may be over-complicating is implementing the IC. I may have been slightly frustrated and defensive when I wrote some of my previous replies. Sorry. I just want to concentrate on the software.
To summarize.
As long as the IC is implemented as detailed in the data sheet and all other nodes follow the standard, it shouldn't matter if the IC is 5V or 3.3V (from a practical viewpoint). The bus cable should be impedance matched with the termination resistors. The cable should be a twisted pair. Grounded shielding is optional. A common mode split termination can be used to reduce EME, but will increase current consumption when transceivers with different common mode voltages (which is likely to be my scenario).
If you think my summation is wrong to the point that I may get in trouble, please let me know. I will start drawing the first schematic layout now. This is a private project so I will open source everything and probably post it somewhere on the forum for review/criticism when I have the first draft ready.
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