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LMK04133 preset CPout1 voltage level

Other Parts Discussed in Thread: LMK04133

Hi Team,

One of my customer use LMK04133.
They consider LMK04133 "free running" before input clock insert to CLKin for PLL1.
In this case, LMK04133 operate with VCXO and PLL2 only, but output usually stable.
Recently, they changed VCXO that more larger VCO gain value and they found unexpected offset in VCXO frequency and LMK04133 output frequencies not exactly set that they targeted.
If input clock insert to CLKin and activate PLL1, CPout1 level go up to control tune of VCXO and LMK04133 generate exactly output frequencies that they designed.

However they want to stable output from LMK04133 without input clock to clkin.
Can LMK04133 preset CPout1 to 1.65V without input to PLL1?
Can it possible?
Thank you.

Best Regards,

  • I'm afraid the LMK041xx does not have this capability. The LMK0480x and LMK0482x families could do however however because they have holdover support.

    Perhaps if they tri-state the PLL1 charge pump, then the VCXO will simply drift and stop after leakage makes it reach it's end state. Otherwise they would have to use some external circuit to force the voltage, then turn it off. The external circuit would cause some sort of leakage which could increase PLL1 phase detector spurs.