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TLIN2029-Q1: TLIN and digital isolator communication issue

Giada De Crescenzo
Prodigy 10 points
Part Number: TLIN2029-Q1

Tool/software:

Goodmorning TI support team,

I am facing troubles when trying to communicate with TLIN2029 and digital isolator (SI8631AB-B-IS1). I attached my SCH.

as you can see, I add a 10kOhm R pull up, otherwise RXD pin will remain always LOW.

LIN_TX, LIN_EN and LIN_RX are directly connected to MCU

in this way, the device is communicating, LIN_OUT is between 0 and 12V as I post here below:

What is strange, is that the device is working correclty with MCU for a few times, then it stops working and LIN_OUT pin seems always stuck to GND.

RXD is high = 5V, LIN_RX = 3.3V in recessive state.

in the past, I used to have this SCH and all works fine.

LIN_TX, LIN_EN and LIN_RX are directly connected to MCU.

what do you think?

thank you in advance!

Giada

  • 0
    TI__Guru 51066 points

    Hi Giada,

    RXD is high most likely due to the pull-up to 5V. Note that B3 should be an input and A3 and output to the MCU I.e., RXD is an output going into B3 and out of A3 into the MCU.

    However, the first schematic shows LIN_RX as an input into A3 I.e., should A3 and LIN_RX be an input or an output? Also note that the working schematic shows otherwise where LIN_RX is now an output.

    Hence, I suspect contention issues and would recommend to verify - observing scopes of VSUP, LIN_OUT, RXD, TXD, LIN_EN, as well as the isolator pins during power up to failure and may also try to temporary bypass the isolator to double confirm with the same operation from the MCU, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 10 points

    Hi Micheal, thank you for the fast reply.

    Yes, I know LIN_TX is an output from MCU. please don't consider the port direction in the SCH, I know it could be written with another symbol, but I was struggling with errors in OrcadX, and in this way it works!

    in the meantime I switched OFF alla the supplies and PC. turn all ON again and now the communication works! What do you think? Maybe is better to add an RC to EN1 and EN2 to delay the enable of U8 only when is completely supplied by both 3V3 and 5V_ISOL?

  • 0 in reply to Giada De Crescenzo
    TI__Guru 51066 points

    Hi Giada,

    I am unsure if the isolator requires the sequence and could not determine such by going through the data sheet and would recommend to ensure the power supplies are stable just to be safe, prior to communicating similar to your feedback and may include pull-ups as well on the EN pins, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 10 points

    why you suggest to add a pull up on EN pin? It works fine, I checked it!

    Power supplies are stable as well. Do you have other suggestions?

  • 0 in reply to Giada De Crescenzo
    TI__Guru 51066 points

    Hi Giada,

    If it works fine, no concerns.

    The suggestion was to avoid situations where the isolator device enables itself prior to the supply rails and I/Os are stable, causing glitches or unpredictable cases such as this case i.e., for a more controlled startup behavior if any power-up / power-down sequence is needed, thanks.

    Best Regards,

    Michael.