• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 20 subscribers
  • Views 172 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.

LMX2572EVM: LMX2572EVM parts values

chris svanberg
Prodigy 250 points
Part Number: LMX2572EVM

The data line resistance values for R5, R8, R9, R16, R19, R20, R22 are all 12Kohm, which I'm trying to understand. With the input capacitance of the digital input pins, I would think this would limit the max bus speed.

The EVAL board is running quite slow so no problem here of course, but to meet the 75MHz speed I think this would be a problem.

Could you recommend a different value, or the inclusion of an integrated RC filter with ESD protection like the NUF6406MNT1G , AOZ8175DI or similar?

  • 0
    TI__Expert 5110 points

    Hello Chris,

    I understand your concern, this resistor and capacitance would be forming a low pass filter. The reason why we place these resistors here are to ensure we do no backdrive the device through SPI.

    It is possible to replace these resistors with low resistances and making sure to plug the SPI in after the Vcc - also to ensure SPI is removed before Vcc.

    Hopefully this helps!

  • 0 in reply to Aaron Black
    Prodigy 250 points

    Interesting design choice.

    The "back feed" could have been prevented if the 3.3V from the companion LMK61PDOA2 board was used on the connector on the EVAL board.
    I added 0R Ohm jumper R21 on the LMK61 board to allow 3.3V to the ribbon connector, then a thin wire from the EVAL pad to the 3.3V input, which could have been done by TI.
    Alternatively a bus switch could have been used that would engage the data pins once the 3.3V becomes active. SN74CB3Q16244DLR

    10K is series with a fast data line is not optimal.