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UCC5606: SCSI Interface shutting off during cold temperatures.

RuggedEngie
Intellectual 375 points
Part Number: UCC5606

Hello,

We are verifying this product works down to 0C and we have been seeing SCSI interface failures around this temperature. The system current begins to bounce around (~0.5A to ~0.8A) and the SCSI device is no longer detected. I am not sure the UCC5606 is at fault here but I wanted to verify our design is okay. Questions below:

  • Any reason this device would not function properly around 0C? Is there an internal cold temp shutdown?
We use 3 UCC5606 for termination of wide SCSI bus. 
  • We tie the /DISCNCT pin of each device to TERMPWR through a 0ohm resistor (Rd).
  • We do not chain each /DISCNCT pin together before connecting to TERMPWR

Compare to UCC5606 datasheet pg5, figure 2.

  • 0
    TI__Guru**** 159871 points

    With /DISCNCT pin connected to TERMPWR through 0ohm resistor, output is 110ohm.

    With UCC5606 not being daisy chained, it is possible that there is delay in enable or power down each device. Is it possible that you can tie them together as an experiment?

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Intellectual 375 points

    Hi David,

    I have not been able to perform that experiment yet. I should note the SCSI interface works fine at room temp.

    We did notice yesterday that we only provide TERMPOWER from the SCSI Host only. Meaning TERMPOWER is sourced from only one place and not at the end of the SCSI Bus near the SCSI device. Keeping that in mind, our legacy product used the terminator chip UCC5614 and it observed no issues. With this current design we switched to the UCC5606 chips. The only difference I can tell between these chips is the reversed logic on the Disconnect pin (DISCNCT.) One thing that is concerning however, is that the input current for the disconnect pin is orders of magnitude different between the two chips. 

    • UCC5606 datasheet pg4 - Disconnect input current is 30-50uA
    • UCC5614 datasheet pg4 - Disconnect input current is 30-50mA

    This is a significant difference and I am wondering if one is incorrect (typo?) Could it be likely we are maxing out our current from our single TERMPOWER source with the new chip? Or could there be some other difference between the chips causing our issue? 

    I think I noted above the we do notice our current meter bouncing around 0.5A to 0.9A during the failure event.

  • 0 in reply to RuggedEngie
    TI__Guru**** 159871 points

    Mark

    For UCC5606, the Disconnect input current should be in uA, mA is the typo on the UCC5614 part.

    Thanks

    David