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TCAN4550: Vsup and VIO voltages

eytan dahan
Prodigy 80 points

Part Number: TCAN4550

Tool/software:

Hey , 

We use in our design the TCAN4550 and supply it with 2 different power sources for Vsup(12V) and VIO(3.3V)

We have in our design the possibility to turn off the 3V3DC_P via switch with Fet as below 

We found that when we turn OFF the VIO only (Vsup is still 12V)  , we still see a voltage on the 3V3DC_P (~1V) 

Only after disconnecting the TCAN4550 , VIO become 0 as we expected.

This voltage can come from the Data signals (are PU to 3V3DC_P) or via the VIO.

1. Do you have an idea why its happening ?

2. It is ok to turn OFF the VIO when Vsup is still 12V ?

  • 0
    TI__Mastermind 36191 points

    Hi Eytan,

    The VIO supply is used for two purposes.  The first is as a reference voltage for the Digital IO (SPI) level shifter circuits and this voltage should match the MCU.  The second purpose it to supply the crystal/clock circuit on the OSC1/2 pins.

    It is OK to remove the VIO voltage when the device is being placed into Sleep Mode because doing so disables the high-speed (OSC) clock which powers the digital core and MCAN controller.  The SPI communication with the MCU is also disabled.

    When the device enters Sleep Mode, the default configuration of the nWKRQ will cause it to output 3.6V that comes from an internal supply sourced from the VSUP supply.  I see there is a 10k pull-up resistor R1263 between the nWKRQ pin and the 3v3DC_P which could be the source for the voltage you are seeing on VIO.  The nWKRQ pin can be programmed to be an open-drain that requires an external pull-up resistor to the VIO supply which would prevent the pin from outputting 3.6V in Sleep Mode.  I would suggest verifying the configuration of the nWKRQ pin and either make sure it is an open-drain, or remove the 10k pull-up resistor R1263.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 80 points

    Many thanks , 

    Indeed the voltage we see is from this Pin nWKRQ , so we have a current flow through the PU resistor R1263 and the serial resistor R3901.

    If this functionality is not in use , can this pin be floating ? (Removed R1263 and R3901)

  • 0 in reply to eytan dahan
    TI__Mastermind 36191 points

    Hi Eytan,

    Yes, if nWKRQ pin is not needed in the application, the pin can be left floating and R1263 and R3901 can be removed.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 80 points

    Great many tanks