CDCM9102: Provide input clock of PCIe interface for DSP c6678

Amy Luo

Part Number: CDCM9102

Hi team,

When the output clock of CDCM9102 is LVPECL level, Voh min (2.12V) is slightly less than VIH min (2.135V) of LVPECL level of c6678 input interface. Can this be connected directly?

If use CDCE62002, it should be able to connect directly. However, CDCM9102 is dedicated to PCIe. I'm rather confused about which one to choose.

Best Regards,
Amy Luo

over 3 years ago

0 Amin Eshraghi over 3 years ago

TI__Expert 6140 points

Hi Amy,

What device is the "c6678"?

CDCM9102 for a 3.3V supply provides:

Vol max of 1.75V (with Vol min of 1.3V)
Voh min of 2.12V (with a max of 2.57V)

If the spec is indeed 2.135V then yes, the 2.12V would be marginal. But I don't know the device to confirm this. However since CDCM9102 Voh is dependent on the VDDx supply, an approach can be to increase that to meet the minimum.

CDCM9102 for a 3.4V supply provides:

Vol max of 1.85V (with Vol min of 1.4V)
Voh min of 2.22V (with a max of 2.67V)

Thanks and regards,

Amin

0 Amy Luo over 3 years ago in reply to Amin Eshraghi

TI__Expert 6890 points

Hi Amin,

Thank you for your reply.

The DSP is TMS320C6678ACYPA25. I found this value in the table on page 6 of the document "Clocking Design Guide for KeyStone Devices". I do not know if I have a wrong understanding of this parameter.

Clocking Design Guide for KeyStone Device:www.ti.com.cn/.../sprabi4

0 Amin Eshraghi over 3 years ago in reply to Amy Luo

TI__Expert 6140 points

Hi Amy,

I would go off of the datasheet values in https://www.ti.com/lit/ds/symlink/tms320c6678.pdf?ts=1598656653328&ref_url=https%253A%252F%252Fwww.ti.com%252Fstore%252Fti%252Fen%252Fp%252Fproduct%252F%253Fp%253DTMS320C6678ACYPA25

Thanks and regards,

Amin

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CDCM9102: Provide input clock of PCIe interface for DSP c6678