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TUSB321AI: CC pins are not working well

Benedek Bús
Prodigy 10 points
Part Number: TUSB321AI
Other Parts Discussed in Thread: HD3SS3212, TUSB321

Hi,

We have a project where we use your TI products for USB-C connector (TUSB321AI, HD3SS3212).

We have a problem with the behaviour of the CC1 and CC2 pins of the TUSB321AI.

We want to use the IC only in DFP mode, so there is no 887k pull-up on the VBUS_DET pin. The CURRENT_MODE pin is unconnected.

(https://www.ti.com/lit/ds/symlink/tusb321ai.pdf?ts=1710414592628&ref_url=https%253A%252F%252Fwww.ti.com%252Finterface%252Fusb%252Fproducts.html)

 

There are two different measurement results:

Case 1

I tried different USB C converters (e.g. USB C - USB A conv.), flash drives…

We measured 0V on one CC and 0.4V on the other. We do not understand why one CC goes down to 0V. We expect 5V here instead of 0V. The 0.4V is correct because we left the CURRENT_MODE pin unconnected. DIR output is always set correctly.

(https://www.ti.com/lit/ds/symlink/tusb321ai.pdf?ts=1710414592628&ref_url=https%253A%252F%252Fwww.ti.com%252Finterface%252Fusb%252Fproducts.html)

 

We tried to put the 887k PU on the VBUS_DET pin, then the previous 0V CC signals go up to 5V. What could be the reason?

 

I also made a scope plot of the behaviour of the CCs (cc1-cc2.png attachment).

 

 

Case 2

We plugged an Active cable into our USB-C connector and left the other end of the cable free.

In this case one CC is always 80mV and the other is always 5V. We think that the measurement result is correct in this case considering the following diagram.

 

(Adding USB-C to your Carrier Board Design - Part 1 (toradex.com))

 

Best regards,

Benedek

  • 0
    TI__Mastermind 22185 points

    Hi Benedek,

    Thanks for reaching out. Can you share the schematic for your design?

    If you'd like to share it privately, you can direct message me through E2E by accepting my friend request.

    Benedek Bús said:
    We measured 0V on one CC and 0.4V on the other. We do not understand why one CC goes down to 0V.

    What is the voltage level on the CC pins when nothing is attached to the port? For a DFP only, this should be 5V on both CC1 and CC2.

    Does this image show the CC1/2 lines at device attachment? If not, can you show the CC lines at attachment?

    Best,

    Shane

  • 0 in reply to Shane Hauser
    Prodigy 10 points

    I send you the schematic by direct message.

    The voltage level is 5V on the CC pins if nothing is attached. The scope plot was taken at the time of attachment when the CC lines go down.

  • +1 in reply to Benedek Bús
    TI__Mastermind 22185 points

    Hi Benedek,

    The schematic doesn't show the full connection to the type-C port, but the 321 implementation looks ok.

    Benedek Bús said:
    DIR output is always set correctly.

    If DIR is set correctly, then your connection should be enumerating. This shows that the 321 is detecting the orientation.

    Benedek Bús said:
    We measured 0V on one CC and 0.4V on the other. We do not understand why one CC goes down to 0V. We expect 5V here instead of 0V.

    When the CC pins detect a device, one of the lines (either CC1 or CC2) will be chosen for orientation and communication between the DFP and the UFP. This CC line will drop to a lower voltage and communicate the current mode. This is the 0.4V line you are seeing.

    The other CC line is not used for communication, and the pullup is disabled in our device. You can see in the datasheet how both lines respond to attachment. This looks similar to the waveform you've shown

    Benedek Bús said:
    In this case one CC is always 80mV and the other is always 5V. We think that the measurement result is correct in this case considering the following diagram.

    In an Active cable connection, the other CC line will be used for VCONN. The TUSB321 will sense the termination (Ra) on the unused CC line and determine that VCONN should be provided. This pulls the unused CC line to 5V, which gives power to the active cable that is plugged in. I agree that this behavior seems correct.

    Benedek Bús said:
    We tried to put the 887k PU on the VBUS_DET pin, then the previous 0V CC signals go up to 5V. What could be the reason?

    This is interesting. Do you mean that the unused CC line is going to 5V instead of 0V? I would expect the other CC line to go low if there is not an active cable connected. If you could show the waveform of CC1/2 at device attachment with VBUS_DET and without VBUS_DET populated, that would be helpful.

    Can you show how the VBUS is controlled in your schematic? If the VBUS is always on, there could be an adverse affect on VBUS_DET.

    Best,

    Shane

  • 0 in reply to Shane Hauser
    Prodigy 10 points

    Hi Shane,

    Thank you for your help. Based on the figure above we now understand how the IC works. The VBUS_DET measurement is no longer relevant for our project. Thank you again!