DS125BR401A Issue

Ian, 

CHA settings EQ=03 and VOD=AF are the maximum settings.  I don't know the losses of your motherboard or AIC, but it seems that lower EQ and VOD could improve the system response.

I would start with EQ=01 and VOD=AB.  I generally expect the CPU and endpoint to begin any link training with Tx Preset 7 which already has a significant amount of boost.

Regards,

Lee 

Dear Lee, 

We using lower EQ and VOD but the result no any change. Would you pls help to double confirm schematic is fine?

Thanks, Ian.

Hi Ian,

I looked at the schematic and it looks fine. I noticed that VDD_SEL is tied to GND with a 1k resistor, and this can be replaced by a zero Ohm. However, this should not affect the way the redrivers behave.

I am wondering if your settings are being programmed correctly. Can you send us a register dump of the settings for one of these redrivers (for example, a register dump of the 0xB0 device)? In particular, I want to double-check that Reg 0x06[3] = 1 to enable the changes to EQ, DEM, and VOD settings to be active.

Thanks,

Michael

Dear Michael,

We did 2 experiments with different setup as at attach.

Customer's application block as SKU1, DS125BR401 in Riser board, eye will be margin.

In SKU2, we move DS125BR401 to NVME Card, eye will be perfect and is very good.

I send schematic and layout yesterday is Riser Card, it looks good for schematic and layout.

Do you have idea what cause worse eye diagram?

Thanks, Ian.

Hi Ian,

I don't think I received the schematic.  Which DS125BR401A inputs are connected to the MB PCIe Slot Tx signals?  The DS125BR401A B-side inputs are more sensitive to the device setting and placement within the overall channel.

Thanks and Regards,

Lee