CDCM6208: Is the VDD_PRI_REF connection to VDD necessary when using only the secondary input

katsuhiro.a.fujimoto

Part Number: CDCM6208

We use only secondary input for xtal input and VDD_PRI_REF is left open, and PLL is not locked.

Do we have to connect VDD_PRE_REF to VDD if we don't use the primary clock input?

0 Kadeem Samuel over 2 years ago

Fujimoto-san,

Is the REF_SEL pin pulled high? If this pin is pulled low, then the PRI_REF inputs are selected for the PLL.
Please see this post for guidance on connecting the inputs when unused: https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/283561/termination-of-unused-clock-inputs-on-cdcm6208

Thanks,

Kadeem

0 katsuhiro.a.fujimoto over 2 years ago in reply to Kadeem Samuel

Hi Kadeem,

Thank you for your replay. The REF_SEL has been pulled high since we tested at the first time, which means the secondary input has been selected.

We continued to investigate the issue on our side and found giving power to VDD_PRI_REF was needed even if we did not use the primary input.

Best,

Fujimoto

0 Kadeem Samuel over 2 years ago in reply to katsuhiro.a.fujimoto

Fujimoto-san,

Thank you for letting us know. I will record this so that we can update the datasheet with this information.

Thanks,

Kadeem

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