TUSB546A-DCI: DP AUX signal only have negative portion after TUSB546A

Phil Chen

Tool/software:

Hi Team,

Our design uses TUSB546A for USB-C DP Alt source function. We encounter a DP no display problem. After trace SBU and AUX signal from USB-C to TUSB546A, I found Source side output AUX/SBU to sink but sink replied signal AUX+ disappeared. Schematics and waveform as followed.

USB-C4-DP.pdf

5 months ago

0 Phil Chen 5 months ago

Prodigy 50 points

0 Vishesh Pithadiya 5 months ago in reply to Phil Chen

TI__Mastermind 38685 points

Hi Phil does the AUX also feed into the PD controller?

Can you share block diagram of the system + full schematic?

0 Phil Chen 5 months ago in reply to Vishesh Pithadiya

Prodigy 50 points

No, AUX/SBU just feed into TUSB546A.

This is block-diagram of this port.

0 Vishesh Pithadiya 5 months ago in reply to Phil Chen

TI__Mastermind 38685 points

Thanks for the info, its odd that we only see this issue on the negative path. Are able to see if there may be an issue in soldering? The P and N are muxed together so if we see one we should see the other.

0 Phil Chen 5 months ago in reply to Vishesh Pithadiya

Prodigy 50 points

We found this issue on many board, not dedicate on one board, Odd message could pass but even message blocked is not reasonable for soldering.

We also found another cable work well and it DC offset is different. AUX+ DC bias is ~4.38V, it is higher than ~1.5V of problem one.

This is ok cable's waveform between TUSB546A and MT8195.

0 Phil Chen 5 months ago in reply to Phil Chen

Prodigy 50 points

We found this failed cable have built-in chips and have unidirection. The marking of source and sink seems wrong. If we reverve connect this cable, the aux signal will become normal.

+1 Vishesh Pithadiya 5 months ago in reply to Phil Chen

TI__Mastermind 38685 points

Hi Phil,

Good find, yeas it seems that one cable used had an issue. The DC bias of the AUXp should be 3V and AUX- should be 0.3V. I'm not sure where the 4.38V is coming from, but it it enables the AUX to send across, it should be ok.

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TUSB546A-DCI: DP AUX signal only have negative portion after TUSB546A