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MAX3243: Only works normally when bps set to 9600

daniel
Genius 5095 points
Part Number: MAX3243

Hi Team,

We use MAX3243EC in our project, the issue is, it works normally when bps set to 9600, but it returns a code corrupt if set to any higher bps.

Also we use the same circuit as the recommended loopback test circuit in the data sheet. Could you give us some suggestion? Thanks

The fail waveform as below.

  • 0
    TI__Mastermind 25705 points
    Daniel,

    I'm sorry to hear your problem. What is your supply voltage, 3.3V or 5V? How're the extra capacitors configured? Is there any current limiting from the supply? What's the loading of the Dout? I'm looking forward to your answers.

    Regards,
    Hao
  • 0 in reply to Hao L
    Genius 5095 points

    Hi Hao,

    Here are the picture of 3243 to RS232 connector.

    The P3V3_STBY has no current limitation for 3243 chip.

    The COM loopback test will have the signal sent from TXD to RXD, so the loading of Dout is the Din of 3243.

    Thanks

  • 0 in reply to daniel
    TI__Mastermind 25705 points

    Daniel,

    To be honest, the schematic looks good to me. Can you double check your loop back connection? If the connector is DB9, usually pin 2 and pin 3 are shorted. You can refer to this article. When it goes to IC level, the Dout shorted with one of the Rin. Please let me know if it makes sense.

    Regards,

    Hao

  • 0 in reply to Hao L
    TI__Guru 62920 points
    Hi Daniel,

    I just wanted to check back in - have you had any luck in debugging this? I think Hao's comments about checking the connections makes sense, since if you have two different output lines shorted together you may see waveforms like this. (The combined output will be high if both outputs are driven high, will be low if both outputs are driven low, but could be at an intermediate state if the two shorted outputs are driving opposite one another.) It may help to debug if you probe the DIN lines along with the DOUTs to see if the "drooping" of the signals corresponds to a particular data pattern. It could also be useful to double-check the V+ and V- signals to see if they show the same behavior.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Genius 5095 points
    Hi Team,

    We change C564,C565,C566,C567 from 0.1uF to 0.47uF and the issue seems solved.
    Any reason about these capacitors affect the code corrupt?

    Thanks
  • 0 in reply to daniel
    TI__Mastermind 25705 points

    Daniel,

    Theoretically what matters is the capacitance ratio between the flying cap and the storage cap. You can refer to this post for the detail.

    To debug the issue, you can disconnect the loading from all Tout pins and check the voltage of V+ and V- pins. Without any loading, V+ and V- voltage should stay around 5.4V and -5.4V. You can also compare the V+ and V- voltage between two capacitor configurations. If they all look good, you might be able to figure out the cause by adding the loading back one by one.

    Please let us know if the information helps.

    Regards,

    Hao