TUSB546-DCI: What's the normal behavior of DP AUX chanel when measure AUX eye diagram?

Simon Chang

Prodigy 40 points

Part Number: TUSB546-DCI

Our project uses the Type-C for usb3.1 and DP functions, but in the debugging process we found that

DisplayPort AUX channel eye diagram failed when AUX snooping disable (pin CAD_SNK PU to VCC).

We use GPIO mode control,

So,

1.Please help to check which AUX snooping should be enable or disable when measure eye diagram?

2.The result of eye diagram is different between AUX snooping enable and disable, please check which is normal?

AUX snooping disable, result failed:

AUX snooping enable((pin CAD_SNK by internal PD )., passed:

3. The eye diagram on AUX snooping enable seems unexpected though eye diagram show passed, the waveform ramp down consistance...

Thanks!

over 6 years ago

0 David (ASIC) Liu over 6 years ago

TI__Guru**** 157606 points

Simon

Can I please take a look at your schematic? Are you using differential probe for the AUX eye diagram measurement? If so, can you please put 0.1uF AC coupling capacitors on the differential probe?

Thanks
David

0 Simon Chang over 6 years ago in reply to David (ASIC) Liu

Prodigy 40 points

Hi David:

Yes, the differential probe P6248 with scope model: MSO72304DX were used for AUX exy diagram measured.

The schematic as attached.

Thanks!tusb546_schematic.pdf

0 David (ASIC) Liu over 6 years ago in reply to Simon Chang

TI__Guru**** 157606 points

Hi Simon

Since you are using differential probe, would you please put AC blocking caps on the differential probe or using high impedance probe without AC caps for the AUX eye diagram measurement?

Thanks

David

0 Simon Chang over 6 years ago in reply to David (ASIC) Liu

Prodigy 40 points

Hi David:

After put AC blocking caps on the differential probe and got good waveform as below:

No ramp down behavior..

Besides, could you let me know if AUX snooping should be enable or disable? And what’s discrepancy?

Thanks!

Simon

0 David (ASIC) Liu over 6 years ago in reply to Simon Chang

TI__Guru**** 157606 points

Simon

AUX snoop is used for power management. The TUSB546 snoops AUX writes to DisplayPort sink’s DPCD registers 0x00101 (LANE_COUNT_SET) and 0x00600 (SET_POWER_STATE) and will disable/enable lanes based on value written to LANE_COUNT_SET. The TUSB546 disables all lanes when SET_POWER_STATE is in the D3. Otherwise active lanes will be based on value of LANE_COUNT_SET. If you disable AUX snoop, then you lose this power management feature. Are you still see difference in AUX behavior when AUX snoop is enabled/disabled?

Thanks

David

0 Simon Chang over 6 years ago in reply to David (ASIC) Liu

Prodigy 40 points

Hi David:

Thanks for explain.

It looks like the same between enable/disable snooping. The key is to add AC block caps when use differential probe..

The issue fixed..And we will keep original design to disable AUX snooping.

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TUSB546-DCI: What's the normal behavior of DP AUX chanel when measure AUX eye diagram?