[DRA829] PCIe ref clock AC-coupling capacitor

Takeo Sekiguchi

Expert 3305 points

Other Parts Discussed in Thread: DRA829

Hello,

Is the AC coupling capacitor is required if clock source is DRA829?

If yes, I'd like to know the recommended capacitor value (of C154/C155 on p.54 of PROC079E2A(001)_SCH.pdf).

Regards,

Takeo

over 6 years ago

0 Stanislav Stilyanov over 6 years ago

TI__Mastermind 18400 points

Hi Takeo,

If DRA829 is the clock source for PCIe, then the following design is required:

The DRA829 clock buffer is HCSL type, requiring 50-ohm termination resistors to gnd at the far end. Tracks must be routed symmetrical and shielded (if possible) on the board.

Regards,

Stan

0 Takeo Sekiguchi over 6 years ago in reply to Stanislav Stilyanov

TI__Expert 3305 points

Hello Stan,

I want to confirm that the AC coupling capacitors are not required on PCB according to provided reference design (for DRA829 as clock source). Is my understanding is correct?

Regards,

Takeo

0 Stanislav Stilyanov over 6 years ago in reply to Takeo Sekiguchi

TI__Mastermind 18400 points

Hi Takeo,

PCIe clock output buffer is HCSL type. It requires 50-ohm resistors to gnd to operate properly. AC-coupling may be required on the clock receiver side if input buffer is not HCSL compatible or for other reasons. This, however, should be handled on the receiver side (PCIe daugther board), and not on the main board.

Regards,

Stan

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[DRA829] PCIe ref clock AC-coupling capacitor