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TCAN1051V-Q1: Simplest possible BOM for a listen-only application

Harald Ilg
Genius 3060 points
Part Number: TCAN1051V-Q1
Other Parts Discussed in Thread: TCAN330, SN65HVD233-Q1, TCAN1051

Hy,

we are realizing a listen-only CAN application (OBD CAN logger). We are planning to use the TCAN1051V-Q1 as physical interface.

We assume, that we do not need a common mode choke. Correct?

Can we go without ESD diodes?

The rest of the system can handle a voltage up to 3.6V. Do we really need a 5V supply for the transceiver?

Best regards

Harald

  • 0
    TI__Guru 62910 points
    Harald,

    Yes, a 5 V supply is needed for the transceiver to properly function. Unless your application has very stringent EMC requirements, though, neither the common mode choke or TVS diodes should be needed. These components aren't needed for operation but are sometimes used to improve EMI filtering and transient immunity. The TCAN1051V-Q1 was designed and tested to meet the requirements of most major automotive OEMs without using these components.

    We do have 3.3-V-powered transceivers available as well. You may want to look into SN65HVD233-Q1 (for example) if you need to eliminate the 5-V rail. TCAN330 may be of interest as well given the small-package (SOT23) availability, although the lower absolute maximum voltage range supported on the CANH/CANL pins (+/- 14 V) may be considered too low for OBD applications.

    Regards,
    Max
  • 0 in reply to Max Robertson
    Genius 3060 points

    Hy Max,

    thanks for your precise response. And thanks for pointing us to the 3V types of CAN transceivers. However it seems cheaper to realize a 5V rail than using the more expensive TCAN330. And as you said the limited common mode voltage might be a risk.

    Another question: There is different types of transceivers: One with silent mode, one without. What is the difference between:

    1) Use a CAN transceiver without silent mode and tie the TX pin to 1 (not connect to TX of controller)

    2) Use a CAN transceiver with silent mode and tie Silent mode pin to active?

    Best regards

    Harald

  • 0 in reply to Harald Ilg
    TI__Intellectual 2090 points
    Good question Harald.

    From an electrical perspective, there is no difference between forcing the transceiver output Recessive through tying TXD high (#1), and through placing the device in Silent Mode (#2). Both cases possess the same power consumption from the 5V supply in the TCAN1051. The only perceivable difference is whether there will ever arise a case where your controller may override the strength of the TXD pull-up in #1, and thus introduce an unwanted dominant on the CAN bus. However, in your case, this doesn't seem like a plausible risk.

    In that case, if you are comfortable with tying TXD high to force the Recessive (#1), then you may want to consider the TCAN1042, which possesses a low power Standby Mode. In this case, you may act as a listen-only application in Normal Mode, and then you may conserve power if at any time you want to transition to Standby Mode. You will want to keep in mind that RXD may still toggle in Standby Mode with "filtered" CAN bus inputs, but you should be able to handle these in your software implementation from the controller side.

    One other note, if you do opt for the TCAN1042 and tie the TXD pin high, then any change to a full transceiver functionality in the future will require a hardware change on the TXD pin (removing the pull-up), whereas if you go with option #2 and use Silent Mode, then a change in the future to a full transceiver will only require a software change of the control pin (S).

    Do these options make sense?

    Thanks,
    Max Megee
    TRX Applications
  • 0 in reply to Max Megee
    Genius 3060 points

    Hy Max,

    thanks for your response. We definitely will stay in listen-only mode, in fact we need to prove with hw desgin documentation that we won't be able to send at any time. So tying TX to VDD seems like a good option. We won't even connect tx pin of controller.

    With that background: Is there still a need for the 5V power supply? We actually simply tested to supply the CAN transceiver with 3.3V and it seems to work fine. What measurements do you recommend to perform to assure that the transceiver works well in all conditions with a 3.3V power supply? Might it affect the common mode voltage? Temperature? Derating?

    Best regards

    Harald

  • 0 in reply to Harald Ilg
    TI__Intellectual 2090 points
    Harald,

    If you choose to use the TCAN1051(V), then you will be unable to operate the device at a 3.3V supply rail, since the VCC supply under-voltage threshold is set at 3.6V. The TCAN1051 will then enter a protected state, and no CAN messages will pass through the receiver.

    However, there is an interesting case if you decide to implement a 3.3V supply rail with the TCAN1042V. This device has a VIO and VCC rail, but you can supply both of these pins from the common 3.3V supply.

    As we discussed above, the TCAN1042V has a Standby Mode, which implements a low power receiver. This receiver can process bit-widths greater than 1.85us, so for lower speeds it could act as a CAN Bus listen-only mode. This receiver is also supplied off of the VIO pin, which supports lower voltage rails down to as low as 1.3V.
    The VCC pin will once again detect an under-voltage condition for the VCC rail, but TCAN1042V is unique in this case. The TCAN1042V allows Standby Mode to remain functional during UV-VCC if VIO still has power. Thus the listen-only functionality through the low power receiver remains active.

    To sum up, you can implement a low power, low speed (~500Kbps or less) listen-only application if you just want to hook up a 3.3V rail the VCC and VIO pins on the TCAN1042V.
    Otherwise, you will need to supply a 5V rail to the TCAN1051(V).

    Best Regards,
    Max Megee