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DS10CP154A Failsafe Operation

David Escandon
Expert 2175 points
Other Parts Discussed in Thread: DS10CP154A

TI Team,

I would like to get some clarification on the operation of the DS10CP154A 4x4 cross-point switch. In particular, I would like to know your recommendations on how to connect unused inputs.

According to Application Note AN-1194, the recommended approach for internally terminated lines is to generate a external bias voltage using a pullup and pulldown resistor of 8k and 5k respectively.

Could you confirm that this is indeed the best approach to handle unused inputs for this device. Thanks.

-David

  • 0
    TI__Expert 5175 points

    Greetings:

    Please advise what you are wanting to protect from, is it preventing noise switching and  additional power in the input, or is the part set up more for say a 4 channel buffer and the concern is over a channel that is enabled without an input applied?  Understanding the use case better, might change the recommendation.

    Since this is a 4x4, the unused channels are ignored by the switch settings.

    If the part is used in SMBus mode, additional functionality is obtained and the smartPWRD mode can be used shutdown the unused IN and OUT stages.

    If there is concern over a unused channel and it is enabled, the external failsafe pull up (plus to VCC) and pull down (minus to GND) can be used.  Select resistors to set the desired VOS and VID.  Typically a 1k up and down will work for most applications.  They can be raised if too strong or too much bias current.

    Best Regards;

    John Goldie

    DPS APPS / SVA

     

     

  • 0 in reply to John Goldie
    Expert 2175 points

    John,

    Thanks for your response. I have additional information I would like to provide you to see if your recommendation will change one way or the other.

    • For the unused input, I am looking for information on how/if they should be connected. We will never switch to the unused input (input #2), but I want to understand whether I need to provide any biasing or protection for the unused input. This is really about preventing any damage or unwanted operating conditions.

    •  For the three inputs we are using, two of them are driven from devices whose outputs are high impedance until configured by a processor. I want understand whether we need to provide any protection against this, especially as one of these is input #0, which is selected by default on power up. The concern is really that we will not cause any damage to the part, as this will not be a normal use case, just what happens for a couple of minutes during each boot.
    -David
  • 0 in reply to David Escandon
    TI__Genius 13475 points

    David

    The concern with unused inputs on LVDS is that if they are floating near the threshold, then the part will be switching internally which 1) generates noise, and 2) burns extra power.  Given your explanation, I would bias the unused input as John suggested so that it doesn't create issues, and I would not worry about the three other inputs that you are using since having these at the high impedance state is not the normal use case.

    Mark