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TCAN1462-Q1: Is there an issue of using VIO at 5V with a seperate VCC 5V line?

Matthew Pole
Intellectual 340 points
Part Number: TCAN1462-Q1

Hi, due to protection and power restrictions I have 2 x 5V lines. 1 that goes directly to supply the main MCU and the other is a switching reg that is for my transceivers. All of the documentation I see if for different voltages for VIO implementation, can I use if with the 5V from regulator going to VCC and the 5V that supplies the MCU going to VIO to make sure it matches MCU voltage exactly?

Also, should I change my switching regulator to 5.1V instead of 5V to make sure VCC is over VIO?

Thank you!

  • 0
    TI__Guru 53555 points

    Hi Matthew,

    The Vio and Vcc supplies are completely separate domains so there is no requirement that the Vcc is greater than Vio. The configuration that you mention here with the Vio supply sharing the supply with the MCU is prefered so that the references for these digital signals always matches. The only thing I will note is that the device will use the Vio supply to power the low power receiver while in standby mode over the Vcc supply, so you may see more power draw from this pin than Vcc in this state. Other than ensuring the ground references for both supplies are the same, I don't have any other a-typcal considerations to recommend for this configuration.

    Let me know if you have any more questions. 

    Regards, 
    Eric Schott

  • 0 in reply to Eric Schott1
    Intellectual 340 points

    Hi Eric,

    Thank you for the response!

    So what happens if VIO is above VCC? Are there any issues? Also, VCC and VIO will be down at 0V if the transceiver is in standby.

    Just to confirm. I have 4 transceivers on my PCB (2 for CAN and 2 for IsoSPI). Would you suggest what I have mentioen above? 2 5v voltage sources (As my main one only enough current for the MCU). 1 to supply the MCU and all of the 4 transceivers VIO pins and the second to supply VCC pin of all 4? And that both supplies can be 5V instead of VCC being 5.1V and VIO being 5V to make sure VCC is above VIO?

    Many thanks!

  • 0 in reply to Matthew Pole
    TI__Guru 53555 points

    Hi Matthew, 

    There is no issue if Vio is above Vcc. This is an expected use case when the transceiver is in standby mode and only powered by Vio when Vcc may be powered off entirely. 

    If both Vcc and Vio are at 0V, the transceiver will be in an off state and will be unable to recognize wake events. Vio is required for the low power receiver to recognize wake events on the CAN bus and indicate to the MCU using the RXD pin. 

    Having a separate 5V for your digital domain (MCU and Vio supplies) and for your analog domain (Vcc for analog transceiver supply) is a common solution for many applications. There is no requirement for TCAN1462 to have different actual voltages at these supplies, so both Vcc and Vio can be 5.0V supplied by different voltage regulators. 

    Regards, 
    Eric Schott

  • 0 in reply to Eric Schott1
    Intellectual 340 points

    I have seperate wake up sources away from the transceivers so should be ok with the voltage always being dropped when the device it put to sleep. I assume constant 5.1V on VCC is ok? As my switching reg will be 5-5.1V

    One last thing then, would I be better to just use a non-VIO device then? Or is it good practice with a seperate supply to use the VIO option just to link it to MCU suppy as a fail safe? Thanks again for the help!

  • 0 in reply to Matthew Pole
    TI__Guru 53555 points

    Hi Matthew,

    The supply input of 5.0V - 5.1V is within the recommended operating range of the transceiver, so there is no issue supplying the device in this way. 

    In this case I think that the separate Vio input would be a better solution. This will ensure that the digital voltage references for the MCU and transceiver remain the same even during undervoltage or overvoltage conditions on either rail. The non-V device's are more applicable to applications where there is only one 5V rail for all supplies or where pin 5 is needed for some other purpose (with a NC option not interfering here). 

    Regards, 
    Eric Schott