• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 375 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.

Inquiry for LMK04828

Takanori Yuzawa
Intellectual 1490 points
Other Parts Discussed in Thread: LMK04828

Hi team

1. Clock input for OSCin
Customer try to choose reference clock (31.25MHz) for OSCin and this application is not DualPLL.
Datasheet of LMK04828 is described below. In this case, is it possible to input 3.3VCMOS (0-3.3V) with ACcouple?

7.1 Absolute Maximum Ratings
VINmax :VCC + 0.3 V

Electrical Characteristics
PLL2 REFERENCE INPUT (OSCin) SPECIFICATIONS
VOSCin (Input Voltage for OSCin or OSCin* AC coupled; Single-ended )
2.4 Vppmax

2. CLKin
If this application is not used CLKin0/CLKin1/CLKin2, should CLKin be open or connect 100ohm with ACcouple?
And also, could you let me know recommend register setting when CLKin0/CLKin1/CLKin2 and PLL1 are not used

Best Regards,
Takanori Yuzawa

  • 0
    TI__Mastermind 28560 points

    Hello Takanori-san,

    I suggest for OSCin, you use a voltage divider on the CMOS input.  This is how we connect a 3.3 V CMOS output VCXO to our OSCin.  Using 100 ohm series near VCXO output, AC coupling capacitor.  50 ohms to ground near IC, then AC coupling to IC.

    • The reason for the first AC coupling capacitor is to prevent the CMOS output from having a low impedance path (150 ohms) directly to ground.
    • The reason for the second AC coupling capacitor is to prevent the 50 ohms to ground from grounding the OSCin input.

    The 50 ohms at destination gives good RF termination at load, unlike traditional CMOS which uses source termination with series resistance to equal 50 ohms looking backward into driver.  Note, we used 100 ohms in this case so the source output impedance is > 50 ohms.

    ----

    CLKin can be left floating.  These pins will be powered down.  For production reasons, I still recommend placing a small amount of copper trace on unused pins so that the solder fillet re-flow flows the same all around the IC.  This can help keep the IC level during reflow.

    73,
    Timothy