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TUSB2036VF noise issues ?

Other Parts Discussed in Thread: TUSB2036


I'm designing an embedded system using the TUSB2036 USB hub and PCM2707 sound card. On the upstream side, the TUSB2036 is connected to linux computer module. On the downstream side, it is to be connected internal PCM2707 and external usb memory stick. 

The problem is with TUSB2036 i suppose. When I don't connect external pendrive PCM2707 is working without problems. When I connect external memory PCM2707 stops working and in the linux logs i get

Cannot enable port 1Maybe the USB cable is bad?

kern.err kernel: [   22.170000] hub 1-1:1.0: unable to enumerate USB device on port 1

It happens with different isb sticks.

The application schematic is attached below. If anyone with more experience with TUSB2036 can see a problem on the attached schematic, your help would be greatly appreciated. 

  • Hello Lukasz,

       The 15k
    Ω resistors to ground are required in downstream facing transceivers (see the picture below). Some devices have less control on D+/D- than others. Although it is not required to have capacitor (22pF) an implementation may use them at the transceiver for purposes of edge rate control.

    Let us know If you have any further questions.

  • Hi Joel,

    Thank you for your response. I will check if adding 15k resistors solved the problem.

    I have a question yet regarding power supply of usb hub application. How should it look like ? Should I use ferrite bead on upstream port ?

    What are the pcb layout constraints re usb hub?



  • Hello,

      Since your hub is in a self-powered configuration you need a local power supply that furnishes power to any non-removable functions and to all downstream facing ports(see the reference design below).

    Regarding board design I suggest these files :


  • Hi Joel

    Adding these resistors after R23,R24 helped, as the devices enumerates correctly.

    Unfortunately when I added 15k pulldown resistors after R9 and R1 usb card stopped working.

    I thought these resistors are mandatory on every downstream port.

    I also don't understand why PCM2707 at port 1 doesn't work when I remove R10



  • Hello Lukasz ,

    Is the PCM2707 permanently attached?

    Does the PCM2707 work when is connected to the USB host?

    Proper hardware implementation for USB communication is achieved with differential LV-TTL (3.3-V) signaling levels between the D+ and D– lines. For the D+ line, this logic level is achieved by connecting the line to the digital voltage supply (VDDi) through a 1.5-kΩ pull-up resistor.


  • Hi Joel,

    Yes, PCM2707 is permanently attached to the hub.

    Now I am a bit confused how the application with TUSB2036 and PCM2707 permanently attached should look like.

    Should I use two 27 resistors on each D+, D- side and one 1.5k pullup on D+  and 15k pulldowns on D+, D- ?


  •  Hi Lukasz,

    Yes,  per USB 2.0 specification, the differential impedance must be 90-Ω differential or 45-Ω single-ended. Having series resistors between 22 Ω to 33 Ω along with internal resistance of the device ensures that the impedance matches this specification. And on downstream facing ports, Rpd resistors (15 kΩ ±5%) must be connected from D+ and D- to ground.(see the figure below).

    I suggest you this file about solving enumeration errors between USB host and the PCM2707.


  • Hi Joel,

    Another question regarding PCM2707

    I use this card with linux and set the gain to maximum but have only 380mV p-p signal at the output.

    Test signal is 1k sin (recorded 0dB) The outputs of the card are unloaded during measurement. 

    Can you glance once again at the schematic if there are no errors in PCM2707 configuration ?



  • Hello lukasz,

    I would suggest posting in the Audio Converters Forum as they are the experts on this device.