• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 2050 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.

LMK5B12204: Single ended LVCMOS Output Level + 50ohm termination

Nir Alon
Intellectual 640 points
Part Number: LMK5B12204


Hello all,

Assuming VDDO_x is 3.3V, what would be the single ended voltage swing (pk-pk) when driving a 50ohm termination?

Output frequency is 32MHz

I'm measuring about 1.1Vp-p with the above condition, is this what should I expect?

Thanks!

Nir

  • 0
    TI__Genius 16765 points

    Hi Nir,

    The LMK5B12204 should have VDDO_x = 1.8 V for full swing LVCMOS outputs. Using VDDO_x > 1.8 V for LVCMOS would result in reduced swing outputs. I expect such behavior from your setup.

    Regards,

    Jennifer

  • 0 in reply to Jennifer Bernal
    Intellectual 640 points

    Hi Jennifer,

    I've seen this data, it doesn't specify if the LVCMOS driver is terminated with 50ohm or not.

     

    Is this the way the measurement was taken? 

    Best regards,

    Nir

  • 0 in reply to Nir Alon
    TI__Genius 16765 points

    Hi Nir,

    I see your confusion.

    • The LVCMOS driver does not require 50 ohm termination. 
    • Yes, Figure 8-1 shows the test setup used to gather the LVCMOS spec in the datasheet. That is, using a Hi-Z probe.

    Regards,

    Jennifer

  • 0 in reply to Jennifer Bernal
    Intellectual 640 points

    Hi Jennifer,

    Regarding the Hi-Z probe test condition - understood.

    By the way, the LVCMOS driver requirement for a 50ohm termination is per application.

    It's not whether the driver needs termination or not, it is depends on the trace length.

    For a relatively short trace length, it is ok not to put 50ohm termination at the receiver side - by doing so you get the full signal1.8V swing:

    If the trace is relatively long, this will cause signal reflection, then it is necessary to add termination - by doing so you get half of 1.8V swing (In my measurement I used 50ohm termination and measured about 1Vp-p signal swing):

    Best Regards,

    Nir