TPS65994AE: Simple USB-C Alternate Mode Displayport

Hi Tim,

Thanks for reaching out on E2E!

The users guide has the schematic of the EVM in section 9 from Figure 9-1 through Figure 9-7. The layout of the EVM is displayed in section 10.

EVM Users Guide: https://www.ti.com/lit/ug/slvubm1c/slvubm1c.pdf?ts=1660689504558&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FTPS65994QFNEVM

With regards to not using the USB data and USB-C PD, are you referring to disabling them in the GUI, or are you trying to leave the pins relevant to these functions floating in your schematic? 

Thank you,

Kevin

Hi Kevin,

Thanks for your reply. Alas, the schematic images in the Userguide are sufficiently blurry to be un-readable hence my reason for asking whether the actual PDF schematics are available.

What I'm trying to implement is Displayport Source (or DFP if you prefer) over USB-C. Indeed, I only want to do Displayport over USB-C and will not be supporting any USB functionality unless I absolutely have to.

What I don't understand/know how to implement is the HPD functionality which is conveyed between Sink and Source across USB PD messages on the CC line.

I far as I'm aware, the TPS65994AE will decode HPD and apply it to a GPIO, however, there is also a question over whether I need to support HPD at all if I'm sending only Displayport data over the USB-C connector.

Kind regards .... Tim

Hey Tim,

Let me reach out to my team and see what I can gather for you!

I will get back to you soon!

Thank you,

Kevin

Hi Kevin,

Thanks for the lead to this App Note; quite useful. Ironically, although not pertaining to the TI device I originally asked about, the TPS65987D is probably a better fit for my particular application. I'm still trying to digest exactly what if any intermediate circuitry might be required between the physical USB-C receptacle and the DFP_D pins inside the fabric of the FPGA.

I've implemented circuitry for the AUX IN/OUT/EN and a switch to facilitate cable flip. I still need to establish whether the GPOI of the TPS65987D will control the OE and FLIP of this AUX_N/P switch. I have however added a TPD8S300 for port protection.

However, this may all be getting ahead of myself here; as before all this becomes pertinent, the PD controller needs to negotiate a PD contract. As all the circuitry on the FMC card is powered from the FMC 12V supply, I don't require any incoming power from the VBUS pin. Furthermore, as the design intent is to only plug this into a monitor (as I'm only trying to send DisplayPort data) there's a pretty good chance that the monitor won't require any current from VBUS either.

To your knowledge, if I leave the VBUS pins of my USB-C receptacle floating, will the TPS65987D be able to successfully be able to negotiate a PD contract (if no power is required in either direction) thus allowing the device to move onto Alternate Mode configuration?

Kind regards,

Tim

Hi Kevin,

The TPS65987D seems a better fit for my application and have decided to adopt it.

I've read datasheets and EVK user guides and looked at reference schematics .... which seem to cover the PD part of the circuitry well. I believe I now have a solution for the power circuitry part of the TPS65897D including VBUS routing as a default 5.0V DFP_U. All being well, this should allow sufficient PD negotiation to move onto Alt Mode operation.

Looking at the schematics for the TPS65987EVM, I note connector J2 denoted as expansion connector which seems to contain the various controls that I also need for DP Alt Mode operation. Are you able to provide schematics for an DP Alt Mode board that plugs into this connector?

Alternatively, perhaps you have a reference design specifically targeted at DP over USB-C in Alt Mode?

From the TPS65987EVM schematics I assume that the TPS65897D is able to create the SBU1/SBU2 FLIP signal (GPIO1) and the HPD signal (GPIO3). I don't understand however the functionality either behind or in front of the SSMX_DP (GPIO0) or SSMX_USB3 (GPIO2) signals? How are they used to control DP Alt Mode?

I can find no reference across the TI webpages that details more precisely the connection of the four Alt Mode signals and the associated circuitry for them to facilitate DP Alt Mode over USB-C. The app note SLVAE16A informs of device configurations but doesn't actually go into circuit details.

Are you able to shed light or share reference designs for this function?

Kind regards,

Tim

Hi Tim,

I will get back to you tomorrow!

Thank you,

Kevin

Hi Kevin,

It's been a few days .... do you perhaps have an update for me?

Kind regards,

Tim

Hi Tim,

Apologies I haven't had a chance yet!

I have reached out internally and will get back to you once I have an answer to your question.

Thank you,

Kevin