• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 48 subscribers
  • Views 129 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS8509: Digital Inputs Maximum Transient Ratings

Naiden Spasov
Prodigy 70 points

Part Number: ADS8509

Hello,

I have a design with an ADS8509 A/D where due to non-optimal PCB layout the input voltage at R/Cbar input overshoots to 6.5V for about 5ns after a rising edge. HyperLynx signal integrity  simulations with the proper ibis models show about 12mA of current flowing into the R/Cbar input during these overshoots for ~5ns.

Do ADS8509 digital inputs tolerate this transient input current for 5ns? If so what is the maximum transient current that can flow into a digital input, through an ESD clamp diode and into a positive or negative power rail for short period of time (like 5ns or so)?

Thanks,

Naiden Spasov

  • 0
    TI__Expert 8310 points

    Hello Naiden, 

    6.5V on a digital pin, or any pin aside the Rxin pins is outside the Absolute Maximum Ratings for this device and would not be recommended for use in such conditions.  

    Is this happening on a currently functional system?  Does this overshoot happen after every single rising edge or is it infrequent?

    Best regards, 

    Yolanda

  • 0 in reply to Yolanda Gonzalez
    Prodigy 70 points

    Hello Yolanda,

    This does not happen on a currently functional system. I consider a BOM change for an existing product that would result in the above mentioned overshoots happening on every rising edge.

    Thanks,

    Naiden

  • 0 in reply to Naiden Spasov
    TI__Expert 8310 points

    Hello Naiden, 

    So the overshoot is unavoidable? or a requirement for your system? Could you please explain a bit more about your system? 

    We have some devices that have an absolute max rating at 7V, but it would still not be recommended for extended use in those conditions. The recommended supply limit for extended use is typically ≤5.5V for digital supplies. Typically for non-analog input pins the absolute maximum current for a lot of our devices is ±10mA, but again, this would not be a recommended state for extended use. 

    Is there a chance of a BOM or schematic change to limit the current and voltage into this pin? 

    Best regards, 

    Yolanda