• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 20 subscribers
  • Views 116 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.

Original question:

LMK04832: is 560 ohm resistor required for AC coupled LVDS

LMK04832: Two questions about LMK04832 & LMK04828

APPLO ZHANG
Intellectual 300 points
Part Number: LMK04832
Other Parts Discussed in Thread: LMK04828,

Hi: 

Question 1:  Can one LMK04828 DCLKoutX drive LMK04832 CLKin0 with DC-coupled differential LVDS signaling?

Question 2:  560 ohm resistor is required in LMK04828 when using AC coupling LVDS. Is it also require in case of LMK04832?

Thanks!

  • +1
    TI__Mastermind 30270 points
    APPLO ZHANG said:
    Question 1:  Can one LMK04828 DCLKoutX drive LMK04832 CLKin0 with DC-coupled differential LVDS signaling?

    LMK04828 LVDS common-mode voltage is 1.2V, which is lower than the LMK04832 default input stage biasing (about 1.7V). The lower common mode of LVDS is enough to degrade performance in some cases. However, LMK04828 HSDS-8mA common mode voltage is nominally almost exactly the LMK04832 default input stage biasing - this could be DC-coupled without issues.

    You do still need 100Ω differential termination for LMK04828 HSDS-8mA when DC-coupled.

    Also, DC-coupling the LMK04832 input can affect the timing accuracy of the LOS detector. If you are not using PLL1 and automatic clock selection (which requires PLL1) on LMK04832, then this LOS accuracy issue doesn't affect your use case.

    APPLO ZHANG said:
    Question 2:  560 ohm resistor is required in LMK04828 when using AC coupling LVDS. Is it also require in case of LMK04832?

    No, LMK04832 outputs do not require the 560Ω resistor between P/N output pins for a DC current path on startup. The LMK04832 output driver design is modified to prevent this issue.

    If you DC-couple LMK04828 HSDS-8mA to LMK04832 input along with 100Ω termination resistance, the 560Ω resistor is not required on the output of the LMK04828 (since the 100Ω DC-coupled termination serves the same purpose of a path for current between P/N output pins on driver startup).