AM67A: PCIe reference clock

Kanae

Part Number: AM67A
Other Parts Discussed in Thread: BEAGLEY-AI, LMK3H0102, AM67

Tool/software:

Hi Support Team,

Please clarify the following questions from our customer considering AM67A.

(1) Regarding SERDES1_REFCLK0_P/N The BeagleY-AI board is configured to use the internal clock as the PCIe reference clock.
　However, since there seems to be an errata in the SERDES internal clock, is it necessary to use an external clock?
　Considering the use of 8.0 GT/s, there are many restrictions such as the inability to use SSC, so it seems safer to use an external clock.

(2) In case of using an external clock, the AM67x Evaluation board uses the LMK3H0102.
　The LMK3H0102 datasheet states that it supports LP-HCSL output, but is AC coupling via a capacitor unnecessary
when inputting to the SERDES1_REFCLK0_P/N of AM67A74?
　Similarly, when connecting the LP-HCSL clock output of the LMK3H0102 to the reference clock input of a PCIe device,
　is AC coupling also unnecessary?

In the customer's board design, the Hailo-8L PCIe device (BGA) from Hailo is directly connected to the board.

Best Regards,
Kanae

1 month ago

0 Robert Eschler 1 month ago

TI__Guru 52265 points

1 - yes AM67A has several errata items related to PCIe and specifically clocks. I can't say is necessary to use external clock - that is dependent on how you are using PCIe and if the errata items will impact you. But certainly some of the work-arounds for the issue(s) involve using an external refclk.

2 - No in-line capacitor is required. LMK3H0102 can be connected directly to AM67 and PCIe connector/peripheral.

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AM67A: PCIe reference clock