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TIOS1015: Ringing on the output signal

ox
Prodigy 230 points
Part Number: TIOS1015
Other Parts Discussed in Thread: TIOS1025

Hi,

I plan to use the TIOS1015 in an industrial IO application.

There is a lot of ringing/overshoot present on the output signal when connected to a 15 m cable:

These voltages have been measurered at the end of the cable.The cable has a capacity of around 4 nF.

The ringing can be seen with a 560R termination resistance and with no termination resistance.

This is the configuration of the TIOS1015, there is also a 30V-TVS Diode present on the output Signal, not shown in the schematic:

Is this overshoot/ringing expected because of the high slew rate and the impedance of the cable?

Would you recommend add a series resistance on the output?

Does the Rlimit also adjust the slew rate of the output signal?

Thank you

Andreas

  • 0
    TI__Mastermind 32920 points

    Hi Andreas,

    Yes, the TIOS1015 has a very strong driver and a fast slew rate.  The ringing is due to the fast slew rate of the output driver sending a pulse of energy down the cable and reflecting back and forth.  The higher frequency content that makes up the fast slew rate sees the long cable as an unterminated transmission line.  Shortening the cable, or slowing down the slew rate to reduce this higher frequency energy is the only option.

    Unfortunately there are no adjustable settings on this device to reduce the slew rate, and your cable length is probably fixed as well.  So for this device, adding an RC filter is the  only real option and I would suggest both a series resistor and a capacitor if possible.

    We have developed a newer version of this device that is pin-to-pin compatible with the TIOS1015 with slower slew rates.  It is now available if you would like to try that device as well.  Switching to it may be a better solution if you can't easily add a resistor and capacitor to your output.

    The TIOS1025 is currently available in sample quantities and will be fully released in the next few months. https://www.ti.com/product/TIOS1025

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 230 points

    Hi Jonathan,

    ill try the TIOS1025