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Original question:

TUSB217-Q1: Improve Signal Quality Margin for 4m USB 2.0 High Speed Cable with TUSB217

TUSB216EVM: entering shutdown intermittently

Ethan Rhodes
Prodigy 190 points
Part Number: TUSB216EVM
Other Parts Discussed in Thread: TUSB216,

I've been testing our USB 2.0 High Speed cable with 2x the TUSB216 devices and one of the devices will at times not start up. Instead it will enter shutdown mode. The exact behavior appears to be affected by the Boost level selected. 

Our setup is as shown below with the TUSB216EVM boards spliced into the 4m cable at both ends between the Hub on PCA E and connectors on PCA C. 

I am running usb signal quality eye diagrams with both TUSB216 devices held in reset and then enabled both at Boost 0 and then both at Boost 3 to determine boost capability of the part within our system.

What I noticed was that the TUBS216 near the hub in the middle of the cable would not always come up but would remain in shutdown as determined by the CD and ENA_HS pins in Table 1 of the datasheet. With Boost at 0 for both devices, sometimes both devices would start up and sometimes the one device would remain in shutdown. With Boost at 3 for both devices, sometimes both devices would start up and after a few seconds the device near the hub in the cable would then shutdown. At other times (with Boost at 3) the device near the hub in the cable would not come up at all but would remain in shutdown.

I have checked VCC ramp up times and Reset ramp up times to verify the datasheet specs were met and all appears within spec there. 

Do you have any ideas as to what is occurring here when the devices do not come up or do not remain enabled?

Thank you,

Ethan Rhodes

  • 0
    TI__Guru 64326 points

    Hi Ethan,

    Another way you can think of shutdown is as a Idle state where no boosting is enabled. It seems as if the both devices are having trouble entering test mode. The way the device enters test mode can vary depending on what is connected and what the part sees on DP and DM. Testing with two TUSB216 can be tricky at times. I recommend that you power externally both TUSB216s and connect them to your oscilloscope before the Hub 

    May I ask what your application is? Are you developing a active cable?  Typically complaint Hosts and Hubs can drive upto 5m of USB cable before needing a redriver. Two TUSB216 for 4m cable after a Hub may not be necessary to pass the far end eye diagram. 

  • 0 in reply to Malik Barton57
    Prodigy 190 points

    Hello Malik,

    Thank you for your response. I am running signal eye diagrams on live traffic in system so I am not attempting to put the TUSB216 into the test mode. I don't have any fixtures or firmware to engage the test mode. VBUS is staying at ~5V all the way to PCA C and PCA D. 

    I'm not quite sure I understand what you are recommending for where I connect to the oscilloscope. Currently, I am probing on PCA E and PCA D to look at far end eye diagrams.

    The cable being tested is an active 8m cable. We have significant attenuation of the USB signal at the mating connectors from cable plug to PCA C (not USB 2.0 connectors) so my intention was to see if a TUSB216 located on PCA C and (possibly) another TUSB216 located on PCA E could be set up to increase our signal quality margin significantly for both ends of the communication link. We may get away with a single part. 

    My concern is I don't know why the device is at times not boosting the signal and I don't have an explanation why this would be based on the datasheet.

    Thank you for your help.

    Ethan Rhodes

  • 0 in reply to Ethan Rhodes
    TI__Guru 64326 points

    Hi Ethan,

    I was under the assumption that you were using standard USB 2 test fixtures and setup. How are you generating the USB 2 data from the Host? Are there consistent transactions occurring on the bus? Potentially the bus may be going into a Idle state causing TUSB216 to turn off boosting. I do recommend using the USB 2 Test packets to measure the eye diagram of the system. This is what is used in USB 2 HS compliance. In this mode the USB Host will constantly send out test packets and TUSB216 will always enable boosting in this test mode.

    Are you using a high impedance probe when probing the DP/DM lines directly? In this setup TUSB216 will need to see USB 2 HS enumeration of a downstream device of hub to enable it boosting. Probing with a low impedance probe will affect the HS enumeration (& termination) seen by TUSB216. 

    I have tested a similar active cable application with two TUSB216 at either end of a 10m cable. In this case I used the standard USB 2 test packets. You can see any example eye diagram in the thread linked below.

    https://e2e.ti.com/support/interface/f/138/t/873193

  • 0 in reply to Malik Barton57
    Prodigy 190 points

    Hello Malik,

    I am using the following setup and browsing live traffic according to Keysight's recommended setup for measuring signal quality.

    Our final implementation would likely put a TUSB216 on PCA C between the cable plug/receptacle and the interboard connection to PCA D and possibly another TUSB216 on PCA E between the Hub and captive cable connection. We would like to provide margin above just a passing eye diagram to account for cable variance.

    My concern has been that the TUSB216 will shutdown with 2 parts in series and particularly with higher boosts without my knowledge of what is occurring. If there is anything you could point me to in order to verify on the TUSB216 IC as to why it sometimes does not stay enabled I would be more comfortable, particularly if it is some setup issue that wouldn't occur in a final design. 

    Example far end eye diagrams are shown below for only the TUSB216 near PCA C enabled.

    PCA E with Boost 3:

    PCA D with Boost 3:

    Example far end eye diagrams are shown below with both TUSB216 devices enabled.

    PCA E with Boost 3:

    PCA D with Boost 3:

    Thanks, 

    Ethan

  • 0 in reply to Ethan Rhodes
    TI__Guru 64326 points

    Hi Ethan,

    Since both redrivers are relatively close to one another you and you are using boost 3, there is a too much boosting on the bus. I would recommend using Boost level 2 instead.