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ISOUSB211: Schematic Review Request

Peter Grinalds
Prodigy 150 points
Part Number: ISOUSB211

Tool/software:

Hello TI team,

I have design a system that will act as single board computer shield. The ISOUSB211 serves as an isolator between the SBC and the usb peripheral. I am able to connect directly to the peripheral from the SBC, but when routed through the ISOUSB211 I am not getting any pass-through. Would you kindly take a look at the schematic and let me know of any issues you see?

Best,

Peter

  • 0
    Prodigy 150 points

    For further clarification, the 3 voltages listed (5VPi, 1V8_Pi, and 3V3_CTD) are all externally generated. V1P8V2 and V3P3V1 are assumed to be internally regulated.

  • 0 in reply to Peter Grinalds
    TI__Genius 11655 points

    Hi Peter, 

    I took a brief look into this but was not able to tell anything from the schematic.

    Can you please describe the issue you were experiencing in more detail?

    Please give me an additional time to look into this as well.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    Prodigy 150 points

    Hello Aaditya,

    Thank you for taking a look at it. 

    My understanding is that upon a correct startup the isolator should act as a passthrough for USB 2.0. However when I power everything on and connect usb to the primary side, the secondary side is not detected as a usb device. Is there something I need to do to "start it up"? Any perspective is welcome.

    Thank you!

    Peter

  • 0 in reply to Peter Grinalds
    TI__Genius 11655 points

    Hi Peter, 

    Thank you for the description. 

    After looking at the PCB layout you have included, I noticed that there are traces running underneath the ISOUSB211 device. Generally, we highly recommend keeping traces away from underneath the isolator. When traces run underneath the isolator, the creepage/clearance of the isolator is essentially decreased, which decreases the isolation rating as well. This is described in more detail in the "Layout Description" section of the datasheet. Please see the image below as an example of keeping no traces underneath isolator:

    This may not fix the issue you are experiencing, but it will definitely help with the performance of the isolator. 

    I will discuss with my team regarding the information you have provided and give some more suggestions. Have you tested with multiple units?

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    Prodigy 150 points

    Hi Aaditya,

    Thank you for the information. I will be sure to more closely follow the layout guidelines on my next revision. In comparison, I also notice that the host USB device is connected to DD- and DD+ while the peripheral is on UD- and UD+ in the snip that you shared. Is this important or is the unit bidirectional? In my case, the host/peripheral is on opposite sides from the in your snip.

    I have built two boards and both have worked by bypassing the isolator, though I suppose I have only tested the isolator on one of those boards. I will check again.

    Thank you!

    Peter

  • 0 in reply to Peter Grinalds
    TI__Genius 11655 points

    Hi Peter,

    UD+/- means Upstream facing port and DD means Downstream facing port D+. I believe that Upstream means receiving end and Downstream means transmitting end. I would assume this means that the device is meant to be used in one direction. Please allow me to double check this with my team tomorrow.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    TI__Genius 11655 points

    Hi Peter,

    Please disregard my comments from my last post. The ISOUSB211 device can be connected to host or peripheral on either side so my comments are invalid from the last post.

    Please allow me to check with an expert in my team regarding this issue.

    Regards,
    Aaditya V