TUSB8041: USB2 Data Line Biasing Resistors

Philip Orange

Part Number: TUSB8041

In our design we are using the TUSB8041 connected to a Qseven conga-QA5 host. Occasionally (1/50) when we boot up the device the USB 2 hub within the TUSB8041 does not get recognised. The USB3 side it working fine.

We have the following setup:

According to all my research, the pull up and pull downs are there for speed detection. USB HS uses the same configuration as USB FS which is the pull up on the D+ line which is why we have that on the UFP for the hub. The DFP can be either HS/FS/LS so these need pull downs to allow the connected device to negotiate the speed.

According to all the forum post I have read, the datasheet for the hub and the EVAL board, these resistors are not present, yet there is no reference anywhere that these are internal to the TUSB8041.

Before I start removing them from my boards completely, could someone please confirm that these connections are not needed and the TUSB8041 has internal pull up/down resistors or constant current sources on the USB2 D+/- pins.

Thanks

over 2 years ago

0 Malik Barton57 over 2 years ago

TI__Guru 64326 points

HI,

TUSB8041 does have these internal terminations, you should not need these external resistors. Have you been able to capture a wave form on the upstream port D+ and D- during this event?

0 Philip Orange over 2 years ago in reply to Malik Barton57

Prodigy 10 points

Hi Malik,

Thanks for your reply.

Out of interest where in the datasheet does it actually state that they are internal? I have spent hours reading it.

I do not have a capture, I will get one.

0 Malik Barton57 over 2 years ago in reply to Philip Orange

TI__Guru 64326 points

Hi,

The schematic examples in section 9.2.1.2 Detailed Design Procedure show that these resistors are not required. For USB 3 hubs it is implied that these necessary components to complete enumeration are integrated.

0 Philip Orange over 2 years ago in reply to Malik Barton57

Prodigy 10 points

Hi,

Thanks for getting back to me, I just didn't want to remove them based on an assumption without evidence.

I will remove these components and do some further testing to see if this resolved my issue, If I can get it to fail I will get a screen capture.

0 Malik Barton57 over 2 years ago in reply to Philip Orange

TI__Guru 64326 points

Hi,

Sounds good please feel free to post again here if you find your issue persists. I would also take a look at your reset sequence to ensure it is stable.

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TUSB8041: USB2 Data Line Biasing Resistors