SN65DSI84-Q1: Eye diagram poor but output is normal

Zirui Su

Expert 5340 points

Part Number: SN65DSI84-Q1

Hi team,

My customer has encountered a strange issue:

During the eye-diagram test, the LVDS output 0 and output 1 have very poor eye-diagram which are NG:

The strange thing is the output content is normal without issue and here is customer's schematic design:

Please kindly help to analyze the issue and tell us why the eye-diagram is poor, this not only happened on single chip but other chips also have the similar phenomenon that LVDS 0 and LVDS 1 have poor eye-diagram with normal display, thank you.

over 3 years ago

0 David (ASIC) Liu over 3 years ago

TI__Guru**** 177301 points

Hi,

Can I take a look at their layout? Are there any significant difference in the routing of the 4 LVDS channels?

1. Have they tried to swap the probe and see if the issue follows the probe or the channel?

2. Please also double check the DSI84-Q1 thermal pad solder coverage and make sure there is sufficient coverage.

3. You can also try to reflow the DSI84-Q1 and see if it solves the issue.

Thanks

David

0 Zirui Su over 3 years ago in reply to David (ASIC) Liu

TI__Expert 5340 points

Hi David,

I will provide you about their SN65DSI84Q1 layout to you.

David (ASIC) Liu said:
eflow the DSI84-Q1 and see if it solves the issue.

What do you mean about the 'reflow'? Sorry for not quite sure about this method, could you please kindly help to explain this more specifically? Thank you.

0 David (ASIC) Liu over 3 years ago in reply to Zirui Su

TI__Guru**** 177301 points

HI,

Basically you heat and melt the solder again to see if it can create a better solder connection between the thermal pad and the PCB ground.

Thanks

David

0 Zirui Su over 3 years ago in reply to David (ASIC) Liu

TI__Expert 5340 points

Hi David,

Yes they swap the probe and even change the oscilloscope for their test. Here is their SN65DSI84Q1 layout please kindly review it:

The dotted circle is the LVDS line：

0 David (ASIC) Liu over 3 years ago in reply to Zirui Su

TI__Guru**** 177301 points

Hi,

Would you please accept my friendship request? Looking at the screen shot, I don't see an issue with the LVDS routing. But I would like to take a detailed look at the actual layout file.

You can send me the actual layout file in a private message once you accepted my friendship. Can you also send me the actual eye diagram test report?

Thanks

David

0 Zirui Su over 3 years ago in reply to David (ASIC) Liu

TI__Expert 5340 points

Hi David,

Could I send the file to your e-mail? Maybe we could discuss it via e-mail later, thank you.

0 David (ASIC) Liu over 3 years ago in reply to Zirui Su

TI__Guru**** 177301 points

Hi,

I sent you my contact email, please check.

Thanks

David

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SN65DSI84-Q1: Eye diagram poor but output is normal