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TCAN3414: Low power CAN transceiver with high impedance receiver output

Chuck Jenkins
Prodigy 100 points

Part Number: TCAN3414
Other Parts Discussed in Thread: SN74LVC1G125-Q1

We are looking for a CAN transceiver (3.3V) that has a low power enable but also tristates the receiver output.  The TCAN3414 or SN65HVD234DR both have low power disables but the receiver output is still an active output.  Our product wants to parallel a 485 and CAN transceiver and we need both the input and bus sides to disable with the enable input.

  • 0
    TI__Guru 61717 points

    Hi Chuck,

    Please see below as Z for CANH and CANL indicates the output will tristate. You may also consider TCAN1057AV-Q1 (also accepts 3.3 V on VIO), where silent mode ensures the outputs are in high impedance, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 100 points

    Thank you Michael for the prompt response.  It is not the output drivers we are concerned with. It is the RXD output from the receiver to the uP that is the issue. Both of the parts mentioned have enables that disable the drivers but not the RXD output pin. This is usually set high when these parts are disabled.  We are paralleling the transceiver 485/CAN inputs and outputs.  The TI 485 transceivers do shut down the receiver output when disabled but not the CAN transceivers. Product suggestion. Put both a 485 and CAN transceiver in one package.

    I currently use one of the TI level translators to perform the decoupling of RXD from the 485 RXD so that both can live on the uP serial input.  Translators are perfect for this even when level translation is not needed but we want to reduce cost.

  • 0 in reply to Michael Ikwuyum
    Prodigy 100 points

    The TCAN3414 has the statement that the receiver is completely shut down indicating that the RXD pin would be high impedance?

    7.3.1.8 SHDN (Shutdown) The SHDN pin is only applicable to TCAN3414 and is used to put the device in ultra-low power mode. SHDN pin has an internal pull-down resistor on-chip, so if the pin is left floating, the device is in normal mode or standby mode depending on the state of STB pin. Pulling SHDN pin high externally puts the device in shutdown. All blocks (including low power wakeup receiver) are disabled in this mode. SHDN pin has higher priority compared to STB pin.

    In the later paragraph the state of the RXD pin as an output is stated. It does not tristate when in shutdown.

    7.4.4 Shutdown Mode This is the lowest power state of TCAN3414. All internal blocks including CAN driver, main receiver and low power wake-up receiver are switched off and bi-directional CAN communication is not possible. Wakeup over CAN bus is also not possible in this mode. CAN bus pins are weakly biased towards GND and RXD is high in this state,

  • 0 in reply to Chuck Jenkins
    TI__Guru 61717 points

    Hi Chuck,

    I see, thanks for the context. Unfortunately this is not the case for CAN transceivers and would forward your feedback internally. If you may, please share more information on the business impact such as volume, timelines, etc.

    Please further note that CAN transceivers typically leave RXD driven to the recessive / high level when in standby / shutdown modes to help keep RXD active for wake-up features. Hence, should not behave like RS-485. I.e., by design, RXD gets its inputs from the differential CANH / CANL with states, recessive or dominant.

    • To get CANH / CANL to be in high impedance (for RXD to reflect such), you would have to place the device in the protected mode similar to table 7-1.
    • If not feasible, you may  use a simple low cost tri-state gate (SN74LVC1G125-Q1 for example) or switch between the TCAN RXD and uP RXD pins to ensure the MCU sees Hi-Z when CAN is disabled and the gate turned off, thanks.

    Best Regards,

    Michael.