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LMK04828BEVM: OSCin options

Kurt Peters
Prodigy 235 points
Part Number: LMK04828BEVM


In SNAS605AR - March 2013 Revised Dec 2015, there is a major heading: 10.2.2 "Driving CLKin and OSCin Inputs."

That being said, both sub paragraphs only contain references to CLKin.  The last one referencing the possibility to single-ended DC couple into the part. Do the paragraphs apply to both OSCin and CLKin?  More specifically, we have a single-ended input for OscIn that is too hot, but only have a 50 Ohm to ground and decoupling capacitor before the OSCin + pin (AC coupled).  The negative differential is AC coupled to ground.  Is it possible to DC couple the input as shown in Figure 24 and replace the AC coupling capacitor with a resistor to decrease the input voltage to something acceptable so we're not overdriving the part? Do you have any other suggestions to reduce the input voltage? Is it possible to use the single-ended output of a CVHD-950X-100 into the OSCin input?

I didn't notice any register settings to set the OSCin to bipolar.

Regards,

Kurt

  • 0
    TI__Mastermind 28590 points
    Hello Kurt,

    Any of figure 20, 21, 22, and 23 could be used with OSCin or CLKin, provided the input amplitudes are met according to the datasheet.

    There is no OSCin_TYPE and is intended for AC coupling only, so figure 24 is not valid for OSCin.

    On our EVM we use a series 100 ohm resistor at source to create a voltage divider with the 50 ohms to ground. Could you use an ~15 pF capacitor for your AC coupling cap to create a voltage divider with your 50 ohm to ground?

    73,
    Timothy
  • 0 in reply to Timothy T
    Prodigy 235 points

    Thanks for the reply Timothy.  I am not understanding your comment about the 15pF cap.  How would that work, exactly?

    For the single-ended operation, I'm assuming the Voscin on page 11 is right, and not to use pg 10 Vclkin, even though the high is the same (2.4 V) , the low isn't (0.25 or 0.35 V vs. 0.2 V)....?