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TCAN1043HG-Q1: Duration of short circuit fault

Yunmiao Li
Prodigy 60 points
Part Number: TCAN1043HG-Q1

Tool/software:

Hi,

    For the TCAN1043HG-Q1 chip, considering the need for a short power supply test - such as a CANL short power supply, the bus voltage VCANH will increase rapidly, then what is the time for this voltage rise?
    In addition, how to evaluate the time that the chip enters sleep-mode due to short power supply test? Does it depend on the junction temperature?

Best wishes,

Yunmiao Li

  • 0
    TI__Guru 53575 points

    Hi Yunmiao,

    When one of the CAN signals is shorted to supply or ground, the unshorted signal line will follow the voltage of the shorted signal line due to the termination resistance connecting  the two. This is more of a characteristic of the CAN system and how much capacitance exists on each signal line and is largely independent of which CAN transceiver is used.

    The CAN transceiver can typically overcome the short with some regard on the non-shorted signal line, though the signal integrity will be greatly reduced. Driving a dominant signal during a short circuit event will likely have the CAN driver near or at its current limit so heating will occur - though this will not always lead to a TSD event as the CAN protocol will likely detect errors and cease communication attempts (go bus-off). Keep in mind this heating only occurs when the transceiver is actively driving a dominant signal - when the CAN driver is idle recessive or in any low-power mode including sleep mode then no current will be passing through the CAN driver and excess heating will not occur. While idle, CAN transceivers can withstand a bus fault indefinitely as long as the voltage remains within the absolute maximum rating of the CAN pins.

    Let me know if you have any more questions.

    Regards, 
    Eric Schott 

  • 0 in reply to Eric Schott1
    Prodigy 60 points

    Hi,Eric

        1. On the RXD, the resistor is usually pulled up to the VIO to stabilize the RXD's power-on state. Is it necessary to reserve this pull-up resistor?
        2. Generally, pull-down resistors are reserved in the nstb and EN terminals for stable state, so will this pull-down resistance affect the sleep and wake up of the chip?

    Best wishes,

    Yunmiao.Li

  • 0 in reply to Yunmiao Li
    TI__Guru 53575 points

    Hi Hynmiao,

    Yunmiao Li said:
      1. On the RXD, the resistor is usually pulled up to the VIO to stabilize the RXD's power-on state. Is it necessary to reserve this pull-up resistor?

    The pull-up resistor on RXD is to ensure that the signal is in a known state before the transceiver is powered-on. This does not impact the behavior of the transceiver itself. The MCU may be impacted by the RXD pin state during startup as it's possible that the signal could go from low-to-high when the transceiver is turned on when no pull-up is present. If the transceiver and MCU start up at the same time (share a power supply) this resistor is likely unnecessary. 

    Yunmiao Li said:
    2. Generally, pull-down resistors are reserved in the nstb and EN terminals for stable state, so will this pull-down resistance affect the sleep and wake up of the chip

    The biasing resistors on the mode control pins are generally a fail-safe mechanism - in the case where the MCU stops functioning and the transceiver's mode control pins go high-z, these external biases will control the state of the transceiver. We generally recommend this bias be nSTB = low and EN = high. This combination will bias the transceiver into Sleep mode - it's lowest power state. This will ensure that in such a fault case the node will have minimal impact on the rest of the system. 

    Regards,
    Eric Schott