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HD3SS3220: DFP doesn't power up.

Part Number: HD3SS3220
Other Parts Discussed in Thread: TPD8S300

I have inherited a design from another engineer who has now left the company.

It is a single board with 2x USB-C UFP and 2x USB-C DFP

Basically, one of the UFPs passes through to one of the DFPs but goes via a Pair of HD3SS3220 muxes in order to allow for any cable orientation at each port. (so 4 possible cable orientations).

(Each UFP and DFP port also has TPD8S300 for port protection)


Each DFP also has a TPS26600 (eFuse) to switch the DFP power on, and portect against power surge, but only when required. Ie the power won't be switched through from UFP to DFP until a device is detected on the DFP.

However the issue I am seeing is that the DFP power never gets switched on. As I understood it, the CC lines on the DFP should be such that it switches the ID line of the HD3SS3220 (mux) which I then use to drive the enable signal of the TPS26600 (eFuse) however this is not happening.

I can supply full schematics and board layout files in PDF or Altium format, but the UFP->DFP is just one part of a much more complex board.

Can anyone explain why the ID line of the HD3SS3220 is not being assetred (low) when a device is connected to the DFP?