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TLIN1021-Q1: question about the pull on of the LIN bus

zhiyuan zhang
Intellectual 620 points
Part Number: TLIN1021-Q1

Hello Expert,

    Why should we add a 1k pull up in the LIN bus for the master LIN application?

    What happened if this pull up change to 2k,0.5k ,open or something else?

    And if the reverse protect diode is shorted, what happened on the communication?

   Another question,why there should be a pull-up resistor on RX but no on TX?

  • 0
    TI__Mastermind 28530 points

    Hi Zhiyuan,

    1. Because this is specified in the LIN standard specification. LIN uses an open-drain line, so it needs to be pulled up for a valid high-level voltage.

    2. Again this is from the LIN specification. It needs to be exactly 1 kΩ pull-up. The pull-up resistor needs to be small enough so that rising edges are fast enough, and large enough so that no power is wasted. The 1 kΩ value is chosen so that these parameters are correct for the LIN protocol.

    3. If there is a loss of power at the ECU level, the device has extremely low leakage from the LIN pin, which does not load the bus down. 

    4. RXD uses open drain output structure therefore VOL level is based upon external pull-up to VCC (microcontroller supply voltage). If RXD on MCU, or LIN transceiver, has an internal pull-up, then that external pull-up resistor is not required. TXD has already integrated a weak pull-down resistor.

    Regards,

    Sean Guo