CDCM6208: Single-end input clock

Kazuki Itoh

Genius 9175 points

Part Number: CDCM6208

Hi team,

When inputting single-end clock to secondary reference input, how should I terminate SEC_REFN?

Should it be pulled down with 1kOhm resistor?

Also, should PRI_REFN be pulled down with 1kOhm as well?

Regards,

Itoh

over 2 years ago

0 Timothy T over 2 years ago

TI__Mastermind 28540 points

Hello Itoh-san,

Please leave the unused input pin open.

73,
Timothy

0 Kazuki Itoh over 2 years ago in reply to Timothy T

TI__Genius 9175 points

Hi Timothy-san,

https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/283561/termination-of-unused-clock-inputs-on-cdcm6208

In the above thread, it is mentioned that unused pin can be pulled up/down with 1kOhm resistor.

Is it different if the single-end clock is used?

Regards,

Itoh

0 Timothy T over 2 years ago in reply to Kazuki Itoh

TI__Mastermind 28540 points

Hello Itoh-san,

You are correct. I found in another thread the advice to leave open. Let me double check. Certainly with the pull-up/pull-down you cannot go wrong as you can always leave the components un-populated.

73,
Timothy

0 Timothy T over 2 years ago in reply to Timothy T

TI__Mastermind 28540 points

Hello Itoh-san,

It is not required to place any other components with driving CDCM6208 single ended. The only requirements are the Vih/Vil levels listed in the datasheet.

When unused and the input buffer is powered down, there is no need for any biasing, the inputs can be left floating.

If the input is used, but no clock present, the inputs do have hysteresis to prevent chattering as listed in the datasheet. Only if you have excessive noise what would exceed the hysteresis level would the addition of pull-up/pull-down on opposite pins be of any use. You would want to put the pull-down on the pin which is biased at the lower level - which I'm not sure off-hand which pin that is.

73,
Timothy

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CDCM6208: Single-end input clock