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Other Parts Discussed in Thread: LMK03002CEVAL, LMK03002


We have a condtomer that is evaluating the  LMK03002 using the  LMK03002CEVAL.  This customer's application requires that the input to the  LMK03002 be turned off.  When the customer does this the  LMK03002 still outputs a signal.  Here are further details from the customer:

Step1:  We had programed the EVAL Kit Fout output @ 1680MHz, Osc port connected to an external source @ 70MHz.  We are also monitoring CLK0 -CKL3 output.
Step2:  Then we powered the board down for say 1 min,
Step3:  Power up the board again
We noticed

Step 4:  Switched on the Oscillator reference @ 70MHz and got the following output

Step5:  We re-programed the EVAL Kit vi UWIRE for Fout o/p @ 1680MHz,  Osc port still connected to an external source @ 70MHz.

Step6:  Switch off the Osc port still connected to an external source @ 70MHz.  Still have the following outpput:

Question: What's the VCO locking into after input ref is switched off

Thanks for your help.


John Wiemeyer


  • John,

    These results do not surprise me, although I am not sure if "powered down" means that the device is powered down via software or if power is completely removed from the device.   I'm going to assume that it means power is removed from all power pins.  One key point is that the VCO tuning range is actually divided into 128 different frequency bands.  Upon programming the N divider, a calibration is run to determine the proper band.  However, if the input frequeny is changed or taken away and the device is not programmed, then it gets stuck in the wrong band.  Now lets step through your adventures ...

    Step 3:     I am not sureif this device has a power on reset or not, but if you do not hit the reset bit, I am not confident what you might see.  Also, I have seen devices hold their programming information for a long time.  For instance, I have taken a device with no power on reset, changed a component, and plug it back to my spectrum analyzer and it still locks -- although it doesn't happen every time.  I suspect that maybe large bypass capacitors might hold charge.  Anyways, I'm not surprised that you see an output with no programming.    It looks to me like the VCO might be near the middle of the range.  If there was a power on reset, it would probably put the VCO in it's middle range.  I believe there are 128 frequency bands,so it's proably at band 64.  But since there is no input, it is going to tune to the lower end of that band.

    Step 4:  Signal is applied and it causes the device to push the VCO to the upper end of the tuning band it was in.  No programming is done, so VCO has no chance to re-calibrate to another band.  In any case, it looks to me that after the device was locked, which would be to the center of the VCO band it was in, the OSCin input signal looks to be perceived higher than 70 MHz, causing the VCO to go the the upper end of the VCO tuningband.   Might be noise or harmonics.  I don' t think that this OSCin pin self-oscillates with no signal attached.




    Step 5:   No surprise that the device locks after programming.

    Step 6:  I'm not sure what you mean by switching off the OSC port as I see no programnming word to power this off.  Perhaps you mean that you have the reference oscillator attached, but you are powering down the reference oscillator. 

  • Hi Dean,
    Thanks for the details you provided. I believe the customer's main concern was that there was an clock signsal comming out of the LMK03002 when the input reference clock is removed. They were concerned because in their applicaiton it is possible for the input reference clock to be removed and in this condition they wanted the output of the LMK03002 to stop toggeling. The data sheet provide an example how to disable the LMK03002 ouput using the lock signal. The customer is going to try that to determine if it will work in their application.
    Thanks for your help. Regards,John Wiemeyer
  • Keep in mind, by connecting GOE to the MUX output with lock detect, the Fout signal will not be impacted. Only the CLKouts.