LMK04832: Trying to generate 3.2GHz

Corey Hahn60

Part Number: LMK04832
Other Parts Discussed in Thread: ADC08DJ3200

Trying to program a LMK04832 to output 3.2GHz on ClkOut2 using LVPECL2.0. I have attached a TICS Pro project for the part. When I divide by 2 from 3.2Ghz internal VCO i can measure a great 1.6GHz on ClkOut2. BUT if I attempt to divide by 1 and and output 3.2GHz I get an ugly ~1.066 GHz on the output. How do I get 3.2GHz output?LMK04832_TICSProject.zip

over 6 years ago

0 Shawn Han over 6 years ago

TI__Genius 9920 points

"Bypass Div".
The LMK04832 does support LVPECL20 and LVPECL16 modes, but best performance is achieved with CML outputs in bypass mode.
When in bypass mode the even clock output may only be CML.

0 Corey Hahn60 over 6 years ago in reply to Shawn Han

Prodigy 220 points

Do i need to use CML and this bypass mode to reach 3.2GHz? I was hoping not to. Is there a section in the datasheet/user guide that outlines this?

0 Corey Hahn60 over 6 years ago in reply to Shawn Han

Prodigy 220 points

In the end I am looking to drive an ADC08DJ3200 clock input with this output. What do you suggest my interface passives schematic look like between CML and the input clock of the ADC?

0 Corey Hahn60 over 6 years ago in reply to Shawn Han

Prodigy 220 points

5148.LMK04832_TICSProject.zip I am still unable to get 3.2GHz out. I have attached my tics pro project. I can get lvpecl20 @1.6GHz to work correctly, but when i turn on clock divide bypass and change to cml, it goes away. No clock, not even a wrong frequency clock.

0 Shawn Han over 6 years ago in reply to Corey Hahn60

TI__Genius 9920 points

1, Search "only be CML" in datasheet.

2, Refer to LMK04832 EVM user guide,

There is a schematic shows CML output termination circuits, which need two inductors and a 20 Ohm resistor to pull up to Vcc, as below figure.

3, After AC coupling caps, you can set a new bias for ADC. Double check ADC's bias range and VID range (or Vinpp range).

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LMK04832: Trying to generate 3.2GHz