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TIOL1115EVM: Noise on L+

Mira Kim
Prodigy 40 points
Part Number: TIOL1115EVM
Other Parts Discussed in Thread: TIOL1115

I am using the TIOL 1115 EVM along with a IO Link Master from TEConcept.

I have an M12 cable connected to the Master and I cut the other end and stripped the wires to connect the L+, C/Q, and L- lines to the EVM in the TB2 socket (AMP connector where you put in wires and screw in to tighten them in place).

I've noticed that the L+ line is gets noise on every rising edge and falling edges of the C/Q line by almost 100 mV. I am using the LDO to supply 5V to an MCU, so I can't have this much inconsistency. I've tried to research on what the problem could be, and it seems like the wires may be experiencing electromagnetic interference because they are not shielded?

The way TIOL 1115 EVM is designed, if I want to input all three lines (L+, C/Q, L-), I need to connect the wires to TB2 socket, and I don't know if it's possible to have them "shielded" so the L+ line does not get bothered by the C/Q line. Does anyone have any ideas on how to fix this? Did anyone else have this issue?

  • 0
    TI__Mastermind 33220 points

    Hi Mira,

    What is the voltage level you are applying on L+ ? Also, you said you are concerned with the L+ voltage level because you are using the internal 5V LDO to supply your MCU.  Have you monitored the 5V for any variation when CQ switches?  I am not sure from your description whether the 5V level is being affected as well.

    There could be some EMI coupling in the cable because it is not shielded, but it sounds more like a current starve behavior to me that could be fixed by adding some additional decoupling capacitors, or larger valued capacitors on L+.  When you switch the value of C/Q, you are either connecting or disconnecting the C/Q line to L+ which will allow current to flow or stop flowing between L+ and C/Q.  Since L+ is essentially a power supply line, it's current source will have to increase or decrease the current to hold the voltage stable.  This will take some amount of time for L+ source to detect the current change and respond accordingly and I suspect you are seeing the voltage fluctuate as a result.  If this is the case adding some additional capacitors on the EVM should help source the extra current needed during this transition and stabilize the L+ voltage seen at the pin of the TIOL1115 device.  Different cables can create different inductive loads and require different amounts and types of decoupling to offset that inductance.  Small value capacitors will be able to source additional current quickly, but do not have a lot to give.  Larger value capacitors are slower to respond to the current changes but can source larger amounts of current before they become discharged.  Having a mixture of small and large value capacitors in parallel close to the load (in this case the TIOL1115) is usually a good idea.

    Regards,

    Jonathan