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Original question:

TUSB2046B: Hub not recognized, schematic issue?

TUSB2046B: Designing issue

Shubham Yadav
Prodigy 240 points
Part Number: TUSB2046B

Tool/software:

Dear Sir,

We are using TUSB2046B USB HUB in our design for 2 ports. I have followed the designing wrt what mentioned in datasheet whether it may be related to termination resistors or optional filter of 22pf. While designing, I got certain doubts which I want to clarify from your side. Doubts are listed below:

1) As it 4 port hub, we are using only 2 ports so I terminated the DM3,DM4 & DP3,DP4 of other 2 ports by a 15kohm resistors wrt ground, as shown in MSP430F5529IPN eval user guide schematic. I don't know what to do PWRON & OVRCURRENT pin?

2) As we are following MSP430F5529IPN eval kit USB hub design, in that 6Mhz crystal oscillator is used but these part is not available on any website means it is obsolette. Can we use internal 48Mhz  or can you suggest other 6Mhz crystal. So, these USB HUB functions properly.


3) The reset pin of USB HUB which is active low is pulled by a 47K resistor. Can you help me out in knowing how these resistor value is selected as I want to learn. Means, if there is any current parameter which is taken in consideration while selecting this resistor. Can I use 10k resistor instead of these?


4)  As our USB HUB is self powered and we are using only 2 downstream ports. In downstream ports, we are not using any type A device or USB connectors. Means, in our case downstream USB port signals are going directly to our controller USB  2.0 port and one to USB TO UART converter IC. So, sir I need to know is there any need of load switch ? As in MSP eval kit load switch is not used.

Waiting for your reply,

Regards,
Shubham 

  • 0
    TI__Guru** 122810 points

    Hi:

    Shubham Yadav said:
    1) As it 4 port hub, we are using only 2 ports so I terminated the DM3,DM4 & DP3,DP4 of other 2 ports by a 15kohm resistors wrt ground, as shown in MSP430F5529IPN eval user guide schematic. I don't know what to do PWRON & OVRCURRENT pin?

    you can leave PWRON/OVERCURRENT floating is not used.

    Shubham Yadav said:
    2) As we are following MSP430F5529IPN eval kit USB hub design, in that 6Mhz crystal oscillator is used but these part is not available on any website means it is obsolette. Can we use internal 48Mhz  or can you suggest other 6Mhz crystal. So, these USB HUB functions properly

       you need to provide external 48Mhz clock to this pin.

    Shubham Yadav said:

    The reset pin of USB HUB which is active low is pulled by a 47K resistor. Can you help me out in knowing how these resistor value is selected as I want to learn. Means, if there is any current parameter which is taken in consideration while selecting this resistor. Can I use 10k resistor instead of these?

        resistor is picked based on RC on reset pin, need to get min low 100us.

    Shubham Yadav said:
    s our USB HUB is self powered and we are using only 2 downstream ports. In downstream ports, we are not using any type A device or USB connectors. Means, in our case downstream USB port signals are going directly to our controller USB  2.0 port and one to USB TO UART converter IC. So, sir I need to know is there any need of load switch ? As in MSP eval kit load switch is not used.

    If downstream port device don't need VBus, then load switch is not needed.

    Best

    Brian

  • 0 in reply to Brian Zhou
    Prodigy 240 points

    Dear sir, 

    As you mentioned resistor and capacitors are selected based on RC time constant, and in datasheet it is mentioned that RESET should have pulse width between 100us (min) to 1ms and as R=47k and C=100nf so equivalent RC TIME CONSTANT=4.7ms or 4700us which is greater than pulse width. Sir, i am not able to understand could you please clarify.

    2) Sir, based on your response related to 4th points sir downstream device dont need bus. But there is one at which IC mu USB signal is going on and in that IC there is one USB 2.0  port which requires VBUS i/p at its pin to recognize external USB device. So, i think that IC requires VBUS, but that IC operating current is small. So, then there is a need of load switch?

    Waiting for your reply,

    Regards,
    shubham

  • 0 in reply to Shubham Yadav
    TI__Guru** 122810 points

    Hi Shubham:

         For RC time constant, it's fine if >1ms.

        for  Q4: one major reason to use load switch is to prevent over current , once the overcurrent happens, the load switch will send Fault  signal, After hub  received fault signal, hub will send signal to turn switch off.

    Regards

    brian