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ISO7731: output pulse

Ivy Jin
Expert 3145 points
Part Number: ISO7731

Hi team,

My customer found a issue about ISO7731DWR, could you please help review and give some suggestions? Thank you.

The problem is the waveform on the output side OUTC(5pin) and the input side are inconsistent, with a large number of 300ns pulses on the output side .The customer is trying to replace the chip with a new one and the issue still occurs.

However, this issue does not occur when the customer changed the ISO7731 with Nsi8231 or CA-IS3731.

Have you seen similar problems before? Could you please help give some comments? Thanks!

Below is the schematic and PCB layout.

Thanks!

Regards,

Ivy

  • 0
    TI__Mastermind 19815 points

    Hello Ivy,

    Thank you for reaching out. We have seen issues like this before, to make sure, please confirm the points below.

    1. Is this behavior only on OUTC?
    2. Is the same behavior seen on both devices?
    3. I am assuming that yellow is INC and Green is OUTC? If this is not the case, please label the scope traces.
      1. Please provide a scope shot of the Input and the Output channel? 
      2. What is the pulse width of the input (yellow channel)?
      3. If possible, could you provide an input/output channel with a 50Mbps signal? 

    Best,
    Andrew

  • 0 in reply to Andrew Jackiw
    TI__Expert 3145 points

    Hi Andrew,

    1. Yes, only on OUTC

    2. Yes

    3. Yes, the yellow is INC and the Green is OUTC.

    The customer tested it again and found this issue is related to the EN pin.

    When the EN pin is High, the output signal is normal, and when the EN pin is open, the issue will happen.

    Could you please give some comments? Is it possible that the EN has been disturbed due to layout?

    Thanks!

    Regards,

    Ivy

  • +1 in reply to Ivy Jin
    TI__Mastermind 19815 points

    Hi Ivy, 

    Given the information, I suspect that the device is fine. In noisy environments it is possible to see issues when EN is left floating. This would make sense if the enable pin is being intermittently toggled with noise and the device is returning to its default state.

    I would recommend tying this pin to VCC in order to prevent this.