• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 21 subscribers
  • Views 393 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.

LMK00105 - Output noise issue in the customer board

Hiroshi Katsunaga
Mastermind 6480 points
Other Parts Discussed in Thread: LMK00105

Hello,

My customer have a question about LMK00105.

The conditions of the customer as follows.

[Conditions]

 CLKin / CLKin* = LVDS, DC Coupling input

VDD = 3.3V

[Q]

When the state of the LVDS source is Tri-State,  the noises occurs from the outputs of LMK00105 in the customer board.

I attached an example.

This is not the periodic noises.

In this case, the states of CLKin and CLKin* looked Logic High. 

Please teach me what is considered as a cause of the noises.

 

Regards,

Hiroshi Katsunaga

 

  • 0
    TI__Mastermind 32575 points

    Here is one possibility:
    Because the differential inputs are not driven by the tri-stated LVDS driver, the 100-ohm differential termination at the input would "collapse" the internal input offset voltage between CLKin and CLKin*.  Any noise from the system could cause the input and outputs to switch.  Output switching noise from the LVCMOS outputs (or other noise transients from other nearby circuitry) could couple to the input stage and cause the output to chatter or oscillate.

    If the customer wants to avoid noise couping on the inputs from causing chatter when the LVDS driver is tri-stated, they need to maintain some offset voltage between the differential inputs of LMK00105.  This could be done by using AC coupling caps in-between the 100-ohm termination resistor and CLKin/CLKin* input pins; this way, the termination cannot collapse the device's built-in input offset voltage.

    Regards,
    Alan