• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 33 subscribers
  • Views 130 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

SN55116: 8 internal resistor

JOHN DOOLEY
Prodigy 30 points
Part Number: SN55116

We are using SNJ55116J differential line transceiver. we use the A-B input, one input has the option 130 ohm termination at pin 6 which we do not use. 

There is an internal resistor of 8K ohms sourced from Vcc to pull up the input on pin 7. Our circuit has a voltage dived network setup to prove 500 mV at pin 7. When the application was designed, I don't think the engineers took into consideration the internal 8K to Vcc. This pushed 5 500mV reference up to 600mV and varies from IC to IC. I get inconstant result when replacing IC's across date codes. 

My question is:

What is the tolerance of the Nominal 8K internal resistance?

Has the SNJ55116J been revised over the years which might change this 8K resistance pull up? 

  • +1
    Guru 263840 points

    The pull-up and pull-down at the input form a voltage divider. Only their ratio matters, so they are not designed to be precise.

    The maximum II(rec) specification implies that the resistor cannot be smaller than 6111 Ω. You can assume that the tolerances are similar to those of the termination resistor (which has specified minimum and maximum values).

  • +1
    TI__Mastermind 45867 points

    Hi John,

    We don't have a tolerance specified on that resistor - as Clemens mentioned the ratio is what is most important - also as previously noted in this thread the minimum value based on datasheet specifications would suggest 6111 Ohms. 

    The closest approximation would most likely be the RT resistor tolerance which based on datasheet would have a tolerance (assuming nominal of 130) of  approximately

    +28.5% / -41% - and this figure is most likely worse tolerance than 8k nominal resistor (as the negative tolerance magnitude is apprx. -23.6% and |-23.6%| < |-41%| ). 

    There most likely will be a decent amount of variability - so what you are seeing seems to be more or less expected. 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson