LMK04828: Output Frequency Variation

Santhana Krishnan T L

Part Number: LMK04828
Other Parts Discussed in Thread: LMX2582

Hi,

I am using PLL LMK04828 for generating 175MHz from CLKin frequency of 25 MHz with External VCXO of 100MHz. This 175MHz DCLKout has been given as input to LMX2582 PLL for generating 3500MHz.

I observed only 173MHz DCLKout at the output of LMK04828 PLL instead of 175MHz in PLL locked Status. But LMX2582 PLL is not locking with this 173MHz input.

Herewith I have attached the LMK04828 Configuration and LMX2582 Configuration file.

Kindly clarify for adjusting output frequency to out exactly 175 MHz?

over 6 years ago

0 Dean Banerjee over 6 years ago

TI__Mastermind 28001 points

Santhana,

I do not see the attachment.

If the 173 MHz is stable and you try to lock the LMX2582 to it, then it should lock, but you would expect the output frequency to be scaled by a factor of 173/175. However, if you program the LMX2582 before the 173 MHz is stable and then the 173 MHz signal stabilizes, the LMX2582 will be out of lock.

So my suspicion is that this 173 MHz is not stable when the LMX2582 is not being programmed.

What is the VCXO actual frequency. For instance, if PLL1 is not locked and the VCXO is actually operating at 100 x 173/175 = 98.85 MHz, then this would explain everything. In any case, you want to ensure that PLL1 is locked.

Regards,
Dean

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LMK04828: Output Frequency Variation