DS320PR822: Use DS320PR822 as a clock mux

Maxime BOEHM

Part Number: DS320PR822

I'm currently testing a prototype board with DS320PR822. I use this part for PCIe Gen3/4. I also use this part as a clock (100MHz) mux but it is not working. I configured the redriver on "non PCIe signals" using RX_DET function tied to L0 level, and other signals are in the expected state. The input signal is correct but nothing can be plot on the output.

Here an extract from the schematic:

TThanks for your support.

2 months ago

0 Gregory Kobyakov 2 months ago

TI__Genius 10940 points

Hi Maxime,

I can help look over the schematic. How are the MODE and PD pins currently strapped in your application? Also, to confirm, there is no signal at all being output from TX channels on the device?

Best regards,

Greg

0 Maxime BOEHM 2 months ago

Prodigy 40 points

Hi Gregory,

Thanks for your interest. PD is connected to GND and MODE is tied to GND using a 1kR resistor.

I checked on the scope

- (IN) CLK1_GEN_100M_PCIE+/- is 100MHz / 900mV peat-to-peak.

- PD is low.

- SEL is low.

- (OUT) CLK_100M_PCIE_MXM+/-: nothing (low)

...

Maxime

0 Gregory Kobyakov 2 months ago in reply to Maxime BOEHM

TI__Genius 10940 points

Hi Maxime,

Thanks for checking. i will check internally and will get back to you.

Best regards,

Greg

0 Gregory Kobyakov 2 months ago in reply to Gregory Kobyakov

TI__Genius 10940 points

Hi Maxime,

There are few things I would like to verify:

Is the input signal AC-coupled?
Is the device confirmed to be supplied 3.3V via VCC, and is following datasheet power supply recommendations
Are you able to successfully read/write device registers?

Best regards,

Greg

0 Maxime BOEHM 2 months ago in reply to Gregory Kobyakov

Prodigy 40 points

Gregory,

Is the input signal AC-coupled? There are no coupling caps on the PCIe clock (according to the PCIe standard).
Is the device confirmed to be supplied 3.3V via VCC, and is following datasheet power supply recommendations? Powered in 3.3V, power supply recommendations have been followed. I have other DS320PR822 but for PCIe signals and they are working well.
Are you able to successfully read/write device registers? No we are in Pin Mode.

+1 Gregory Kobyakov 2 months ago in reply to Maxime BOEHM

TI__Genius 10940 points

Hi Maxime,

This device expects a AC-coupled signal input on its RX channels. The device is designed with a particular common mode voltage in mind, so a lack of AC-coupling caps will affect this.

Best regards,

Greg

0 Maxime BOEHM 2 months ago in reply to Gregory Kobyakov

Prodigy 40 points

Hi Gregory,

This explains why it is not working... In the datasheet, it's not clearly mentionned that only AC coupled signals are expected on DS320PR822.

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DS320PR822: Use DS320PR822 as a clock mux