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TCAN1043A-Q1: VIO current in sleep mode

Piotr F.
Intellectual 2910 points
Part Number: TCAN1043A-Q1

TI Team, 

TCAN1043A-Q1 datasheet specifies 5uA max VIO supply current at sleep mode

For what TXD state is this values valiud?

My customer is concerned about TXD current source from VIO, taking into account TXD short to GND (in sleep mode).

Is this current source disabled in transciever sleep mode?

  • 0
    TI__Guru 53555 points

    Hi Piotr,

    The Vio pull-up on TXD remains active in sleep mode as long as Vio is supplied. This is done to ensure that TXD remains high for when the transceiver transitions to an active mode so a dominant signal is not inadvertently sent on the CAN bus when changing modes. Generally, this signal will have an external pull-up included or be held high by the MCU if it remains active, so the leakage from this internal pull-up will be negligible. In the case where the MCU pin is left in a high impedance state, the leakage will be very small as the transceiver pull-up is weak and the impedance from the MCU pin will be very large. If a fault case causes the TXD pin to be shorted to ground, this will cause up to 115µA additional current draw from Vio through this internal pull-up (TXD IIL). This short would also make CAN communication impossible from this node as the transmit signal will be stuck in the dominant state. 

    Let me know if you have any more questions. 

    Regards, 
    Eric Schott 

  • 0 in reply to Eric Schott1
    TI__Intellectual 2910 points

    In discussed example TXD pin of TCAN1043Q-Q1 transceiver is driven directly by microcontroller pin. Output driver of this uC pin is supplied from another domain.

    In low power mode of the product, VIO for CAN transceiver stays active, but supply for microcontroller output driver is deactivated. So current can flow from VIO, thru TXD pullup to microcontroller pin, thru it’s ESD protection diode (inside uC) to deactivated supply rail. According to datasheet, this current can be (3,3V-0,4V)/40k = 72,5uA. This leakage is problem for the system. 

    Do we have any TCAN1043xx device that can deactivate pullup in Sleep mode? 

    Or can you think of any solution to cut this leakage path? 

  • 0 in reply to Piotr F.
    TI__Guru 74252 points

    Piotr,

    Thanks for your patience, we will have a response for you after the Thanksgiving holidays.

    Regards,

    Eric Hackett 

  • 0 in reply to Piotr F.
    TI__Guru 53555 points

    Hi Piotr,

    Thanks for your patience over the holiday.

    Unfortunately there is not a way to disable this internal bias. Can the schematic for the customer system be shared? I would like to see how the loginc supplies are used in the system and how the TXD pin is connected to the MCU to see if there is a workaround we can recommend. Do you know what parts on the system are modifiable at this point? Are schematic changes, routing changes, or BOM changes possible? 

    Regards, 
    Eric Schott