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TIOL111: Power supply sensitivity

Paul Dye
Prodigy 180 points
Part Number: TIOL111

Hi, we were recently doing a supply voltage test where we were varying the input voltage to L+ to confirm that our overall design is ok over the range 18 to 30V.

What was found was that when L+ was 30V but the CQ line was still at 24V (we couldn't vary this) the comms were lost. When L+ was wound back down to around 24V, comms were re-established.

I can't find anything in the datasheet which would explain why this would happen but suspect the chip doesn't cope when L+ and CQ do not have similar voltage levels applied.

Can anyone confirm and explain this?

Thanks very much!

Paul

  • 0
    TI__Mastermind 19360 points

    Hi Paul,

    This is an interesting question and I don't have enough information about how you are running your test and what you are using to communicate with the TIOL111.  I'm also not sure if you are implying that you are having errors only when the TIOL111 is in receive mode (EN = LOW) or when trying to transmit data as well (EN = HIGH).  I am unable to duplicate your results and the TIOL111 is designed to work as you desire. 

    With the L+ supply voltage equal to 30V, I applied a signal to CQ, varied it's amplitude from 0V to L+ (30V) and monitored the RX pin.  I have verified that the signal applied to CQ is received and output on the RX pin when the amplitude is as low as approximately 12V for the device I tested.  The Receiver Input Threshold V(THH) range is 10.5V to 13V.  Only when the amplitude fell below the threshold (<12V) was there no signal present on RX.  There should be no problem with your ability to receive a signal with 24V amplitude on CQ when L+ is at 30V. 

    I also verified that I was able to observe a signal on CQ when the EN pin was set to High and a signal was applied to the TX pin.  The signal on CQ amplitude was approximately L+ (30V) as expected.

    You do not indicate exactly how you are running your test, and what you are trying to communicate with, but I find no fault with the TIOL111's ability to communicate under your desired conditions with L+ = 18V to 30V and CQ signal set to 24V.  I also don't know if you are seeing communication error when the TIOL111 is receiving data or transmitting data. 

    Could the communication error be with the other side of the link and the inability of that device to operate greater than 24V?  Can you provide any additional information about your system, or more specific descriptions of when you are seeing the error and how the TIOL111 is configured at that time such as EN = High/Low, scope shots of the waveforms on RX, TX, CQ, L+ etc. that would help isolate the source of the communication error?

    I don't think this is a device error and I suspect there is something else in the system or test setup that is causing this issue.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 180 points

    Hi Jonathan,

    Thank you very much for the effort you put into looking into this, I apologise for not responding sooner.

    The test was run using a common USB to IO-Link master (I won't mention the brand).

    The master steps up the voltages to 24V.

    Within the cable from the master I disconnected the 24V supply L+ and powered it from a bench top supply. I connected the grounds of the bench top supply and the ground on the IO-Link side of the USB master. The CQ line from the USB Master was untouched.

    I was monitoring the communications using a PC application and also the product we are testing has an LED to indicate that comms were lost.

    It could be that the issue is with the USB master not being able to cope with comms messages which would have been higher than it's supply voltage.

    Now you have confirmed that the TIOL111 can operate in this way I think it likely that the issue is with the USB master.

    I will do some more investigation and come back to you if we have more difficulties.

    Thank you for your efforts on this.

    Regards

    Paul