• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 33 subscribers
  • Views 143 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.

DS80PCI402 ENSMBUS pin

Chris Peacock
Prodigy 40 points

I'm working on a design which requires 4 of these repeater devices over 2 links (2 per link). Under normal operation these will be getting the link configuration settings from a resistor array shared between both repeaters, but during initial testing and bring up I would like to manipulate the smbus registers on the devices to work out the optimal settings for the resistor pattern.

I would like to be ale to switch to smbus mode on the fly so have put down a 2 pin header (no jumper under normal usage) for each link where the trace connected to the ICs will have a 499r pull down to GND, and then when fitting a jumper to the header I would enable smbus mode.

I've run the calculations and to meet the voltage level required for this mode I will require a 10.2r pull up. I have a concern that I will be overloading the pin. An example of what I'm looking at doing is below, is this solution acceptable or should I find another solution to this?

  • 0
    TI__Mastermind 29655 points

    Hi Chris,

    Thanks for posting. I believe that your solution for a voltage divider should be acceptable, since the choice of resistance for the pull-up and pull-down resistors make sense with the device's 4-level input to fit logic 1's and 0's when two repeaters are on the line. I don't believe this configuration will overload the pin.

    I understand that the ultimate design is to have the ENSMB pin tied low by default without a jumper. However, would it be possible for you to make a 3-pin configuration where ENSMB is connected to the center pin and the pull-down and pull-up resistors are attached to the lower and upper pins, respectively? You could then just leave the jumper on the lower pin as the default. Would that work for you, too? See attached:

     

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Prodigy 40 points

    Thanks Michael,

    This was the original arrangement I was going to use, however the header will not be fitted during production so having a permanent pull down is a requirement. If there are no concerns over the current into the device then I will go with the option I originally proposed.

    Thanks again,

    Chris