CDCEL913: Spread spectrum clock modulation parameters

Mike DeKoker

Part Number: CDCEL913

Hello,

We are currently evaluating the CDCEL913 for use in one of our designs and are interested in the spread spectrum clocking feature. We've got the CDCEL913PERF-EVM evaluation module and SSC is working just fine. However, section 9.2.1 of the datasheet makes specific references to a couple of modulation control parameters that I cannot find further details for. Specifically, the modulation frequency and shape. I see no reference to these parameters in the Clock Pro software, nor the device registers. Is this a documentation error or can I hopefully just twiddle some undocumented register bits? Does anyone have any feedback or experience with these features? If it's relevant, we're planning on controlling the part via I2C.

Thanks for your time.

over 7 years ago

0 Alan O over 7 years ago

TI__Mastermind 32575 points

Please refer to this forum post, which is also valid for CDCEL913:
e2e.ti.com/.../120597

0 Mike DeKoker over 7 years ago in reply to Alan O

Prodigy 40 points

This is great information, thank you. That explains the modulation frequency. Do you have any information regarding the modulation shape? Figure 16 in data sheet refers to sawtooth, hershey, and sinusoidal shapes.

0 Alan O over 7 years ago in reply to Mike DeKoker

TI__Mastermind 32575 points

It is triangular. The datasheet was just mentioning about other SSC modulation shapes that exist in general and was not intended to be specifically for this device.

Alan

0 Mike DeKoker over 7 years ago in reply to Mike DeKoker

Prodigy 40 points

Upon a deeper dive into the data sheet I suspect that modulation shape is affected by tugging on Vctrl in a VCXO-based setup. Can anyone confirm?

0 Mike DeKoker over 7 years ago in reply to Alan O

Prodigy 40 points

Understood. Thank you, sir!

Clock & timing

Clock & timing forum

CDCEL913: Spread spectrum clock modulation parameters