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I am looking for a widely available CAN Bus transceiver for a project. I have sorted by availability and found two options that seem to satisfy my criteria. However, they both have an extra pin that I do not completely understand the function of, so to my question:

For the SN65HVD266, what is the deal with the VRXD pin? It seems to me like it is some sort of level-shifting pin, but I am confused as it is described as a "Supply pin". In the typical application schematics, the VRXD pin is connected to the 3V voltage regulator, and also the VCC of the MCU, why is this?

The other transceiver is the MCP2562FD, which has a VIO pin, that seems to function in a similar way to VRXD, but here I am also confused by the description.

Could someone please clarify the function of these pins, and how I should connect them when using this transceiver with an ESP32-S3 MCU?

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3 Answers 3

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"Vrxd" is the logic level supply. I guess they named it that way since it only powers the RX pin (the TX signal is driven by the MCU).

The CAN signals require 2.5V +/- 1V so at least 3.5V. This is no problem to achieve if the part is supplied with 5V. Classic CAN transceivers work with 5V logic levels on RX and TX and 5V supply. One example of this would be the MCP2551.

When there is only 3.3V supply available and the MCU requires 3.3V levels, one option is to use 3.3V supply on the transceiver and then tweak the CAN logic levels to 2.5V +/- 0.8V. On example of this would be the SN65HVD230 family.

Yet another option is to provide 5V supply to the transceiver but a variable supply to the logic levels. That's how both the parts you link work. The advantage of this is that you don't have to tweak the CAN logic levels in questionable ways, while at the same time allowing a 3.3V MCU to communicate directly with the transceiver. Most modern transceivers seem to have picked this option.

As for choosing between SN65HVD266 and MCP2562FD, that should be easy. SN65HVD266 is an older part with overall worse protection. Also Microchip is a well-known vendor, while TI is... not recommended for new design, by yours sincerely at least.

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  • \$\begingroup\$ And alas, neither of these parts are available for purchase in the real world because of the on-going semiconductor market psychosis. This includes, but is not limited to, a complete and utter collapse of Microchip and TI logistics chains. Pretty much all CAN transceivers are hard to purchase right now, since the automotive companies have gone bananas and stockpile extreme amounts of them... for the same rational reasons as why everyone started stockpiling toilet paper at the outbreak of Covid 19... \$\endgroup\$
    – Lundin
    Commented May 12, 2023 at 14:28
  • \$\begingroup\$ Thank you very much for your insightful reply @Lundin. Seems like the MCP2562FD is the option to go for then :) I don't recognize what you say about accessibility though. Digikey currenly have 123 825 pcs of the MCP2562FD (8SOIC) in stock, so I don't see this as an issue. \$\endgroup\$
    – eidetech
    Commented May 12, 2023 at 16:13
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    \$\begingroup\$ @eidetech Yeah the SO8 is available but not the DFN. I have both packages in my products and the DFN has barely been available at all during the past 3 years. I'd always go with SO8 if there's board space. \$\endgroup\$
    – Lundin
    Commented May 15, 2023 at 8:08
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CAN is a 5V bus but your MCU may work at 3.3V or 1.8V or whatever and it may not be compatible with 5V at all.

The CAN chips are supplied with 5V supply voltage for the CAN bus, and with another supply voltage for MCU side digital IO which is used to communicate with same voltage levels as the MCU IO pins.

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  • \$\begingroup\$ Thank you very much. Clear and simple explanation. \$\endgroup\$
    – eidetech
    Commented May 12, 2023 at 16:14
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SN65HVD266

VCC = 4.5 V .. 5.5 V
VRXD = 2.8 V .. 5.5 V and VRXD ≤ VCC + 0.3 V

With VRXD the RXD output level can be shifted according to the operating conditions above.
The digital inputs are always 5 V and 3.3 V compatible.
A common use-case would be to connect VRXD to 3.3 V if you have to interface this CAN transceiver to a 3.3 V MCU.

MCP2562FD

VDD = 4.5 V .. 5.5 V
VIO = 1.8 V .. 5.5 V

VIO is the supply pin for all digital pins (that is TXD, RXD and STBY).
This CAN transceiver for example can be used to interface to a 1.8 V or 3.3 V MCU.
Typically you'll instead want to use a MCP2561FD if you don't need the level-shifting property.

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  • \$\begingroup\$ "Typically you'll instead want to use a MCP2561FD if you don't need the level-shifting property" Ideally I'd like to have the SPLIT pin and 3.3V levels both if I could. I wonder why they force their customers to pick one or the other - is the automotive industry still insisting on 5V only? \$\endgroup\$
    – Lundin
    Commented May 12, 2023 at 14:35
  • \$\begingroup\$ @Lundin We've recently switched to the TCAN1057AV CAN Transceiver. It has a VIO pin. And on page 20 they're describing split-termination. (I'm not sure if this kind of split-termination is on-par to CAN transceivers with dedicated SPLIT pins.) \$\endgroup\$
    – Velvet
    Commented May 12, 2023 at 14:40

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