Questions About Using the ADG3304

  Good morning.  I have a customer experiencing a problem with a SPI bus that is going through ADG3304s for level translation.  The bus works fine before they activate the power domain which contains the ADG3304s at which point the bus get very messy and even starts oscillating uncontrollably at times.  They have the following questions:

          1)  They have seen different results when they remove the ADG3304s completely and when we tri-state it.  What is the resistance of I/Os

          during the high-impedance state?

               Rich's Note:  I have sent them information on the output impedance (6k +/-30%) during operation contained in another post.  I am

               assuming that the impedance should be on the order of megaohms but wanted to confirm for the customer.

 

          2)  Their application has two ADG3304s back to back with a long trace in between (please see the attached block diagram).  Is this an

          acceptable use case?

         

SPITopology.pptx
  • 0
    •  Analog Employees 
    on Aug 29, 2013 9:08 PM

    Hi flyerrap18,

    Answers to your questions below:

    1. Yes the high impedance state will have an impedance of MΩ.
    2. The long trace could be an issue as it would add more stray capacitance and other loading effects. This is what is causing the oscillations. The parts are speced to drive specific loads and the long distance may exceed these loads. For best operation the two parts should be close together.

    If you have nay further questions let me know.

    Regards,

    Joe

  •      Joe,

         Thank you for the prompt response.  I have forwarded the information onto the customer.  Thank you.

         Richard A. Pensabene