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TLIN1028-Q1: MCU Reset and LIN Transceiver Sleep Mode

Bettina Lory
Prodigy 20 points
Part Number: TLIN1028-Q1
Other Parts Discussed in Thread: MSPM0L1306-Q1,

Hello

I have a question regarding your LIN transceiver TLIN1028-Q1 in combination with a MCU (MSPM0L1306-Q1).

As recommended in the transceiver data sheet, the ‘EN’ and ‘TXD’ lines are connected directly to the MCU.

We have now found that when the MCU is reset, the TXD signal drops faster than the EN signal and is therefore interpreted by the LIN transceiver as a sleep pattern. The LIN transceiver goes into sleep mode (nRST low, LDO off) and the MCU no longer has any supply voltage:

Thus, resetting the MCU leads to a transition to sleep mode, where an external LIN (wake-up) signal is required so that the MCU wakes up again and responds to LIN communication. In addition, the information about the reason for the reset is lost because there is no supply voltage in sleep mode.

Is it an intended behavior of the MCU-transceiver application that an MCU reset leads to a sleep state?

Best regards,

Bettina

  • 0
    TI__Mastermind 26826 points

    Bettina,

    In many cases, no, I've seen that reset is implemented such that the transceiver enters Standby mode, which as you mentioned is achieved by TXD = HIGH while EN = LOW. Is you MCU driving TXD low? Or is it becoming high-impedance? From systems that we see, TXD becomes high-impedance, so pull-ups present on TXD will ensure that it remains high.

    Best,

    Danny

  • 0 in reply to Danny Bacic
    Prodigy 20 points

    Hi Danny,

    Thank you for your suggestions.

    We thought of another solution: Putting a pull-up on the LIN enable signal, so that it is still high when the MCU is reset and thus no accidental transceiver sleep pattern is created. Since the LIN enable pin is a normal GPIO of the MCU it can then still be pulled low by software, in case sleep mode needs to be entered.
    Do you think this is a good solution as well (instead of a pull-up on the TXD line)?

    Cheers,

    Bettina

  • 0 in reply to Bettina Lory
    TI__Mastermind 26826 points

    Bettina,

    Yes, I think this can work for your system. It is common for designers to implement pull-ups and pull-downs as needed for components like this purely for the purpose of biasing them properly during start-up. Note that the EN pin has an internal pull-down of around 350kΩ. The TXD pin has an internal pull-up already (also around 350kΩ) so unless you expect leakage to overcome this pull-up, just placing your resistor on the EN line should be sufficient.

    Best,

    Danny