TUSB2046B: Intermittent Issue with the USB Hub

Sean Keane

Part Number: TUSB2046B

We are currently having issues with the TUSB2046B and it not being recognised every once in a while. We have seen it many times now and cannot track down the cause. We have scoped the power on and the time seems extremely slow. Our RC circuit on Reset pin incorporates a 15k resistor and 100nF Capacitor.

Any help with where to look would be of great help!

Thanks,
Sean

over 8 years ago

0 Joel Jimenez0 over 8 years ago

TI__Mastermind 18655 points

Hi Sean,

Could you please share your schematics?

Regards

0 Sean Keane over 8 years ago in reply to Joel Jimenez0

Prodigy 60 points

Hi Joel,

Please find attached the schematic.

0 Sean Keane over 8 years ago in reply to Joel Jimenez0

Prodigy 60 points

Hi Joel,

Been scoping the Hub during boot and we have found the following:

Reset is high before clock starts.
Clock starts and runs for around 2 seconds before then dropping out when Suspend becomes high.

Hopefully this provides some more information that could lead to an answer.

Thanks,
Sean

0 Joel Jimenez0 over 8 years ago in reply to Sean Keane

TI__Mastermind 18655 points

Do you have pull down resistors in the downstream ports? Per USB 2.0 spec it is required to use pull down resistors (Rpd) in all the downstream facing ports, this resistors (15 kΩ ±5%) must be connected from D+ and D- to ground.(see the figure below).

0 Joel Jimenez0 over 8 years ago in reply to Joel Jimenez0

TI__Mastermind 18655 points

In addition, you must connect a 1.5KOhm pull-up on DP0.

0 Sean Keane over 8 years ago in reply to Joel Jimenez0

Prodigy 60 points

We have the 15K and 1.5k resistors in the specified places already. We have looked at them already as we picked up the suggestion from another thread on the support forum.

Any other ideas ?

0 Joel Jimenez0 over 8 years ago in reply to Sean Keane

TI__Mastermind 18655 points

Do you have any downstream device attached at power-up?
What OS are you using?
Can you send a scope capture of Vcc, RESET and XTAL at power-up?

0 Sean Keane over 8 years ago in reply to Joel Jimenez0

Prodigy 60 points

No downstream devices connected during our tests but acts the same if we do have them as we have seen the issue a multiple of times.

Windows 10 IoT Enterprise LTSB

This Scope capture shows 5V to our system (yellow) which is dropped to 3.3 and Reset (Blue).

Our tests have shown that VCC and Reset act the exact same during boot which I'm guessing shouldn't happen.

XTAL doesn't begin until Windows begins to load so misses the first 6-8 seconds of boot after power switched on.

0 Joel Jimenez0 over 8 years ago in reply to Sean Keane

TI__Mastermind 18655 points

We recommend a minimum of 100 µs to a maximum of 30ms of reset timing. If the hub is held in reset for a longer period of time, it can fail to respond promptly to USB host signaling and not complete enumeration. This is typically an issue with embedded system applications.

0 Sean Keane over 8 years ago in reply to Joel Jimenez0

Prodigy 60 points

I have found this bit of information on other threads as well but don't know how we can achieve this. We knew this would likely be the cause but were looking for help on how to alter our reset timing ?

0 Joel Jimenez0 over 8 years ago in reply to Sean Keane

TI__Mastermind 18655 points

Hello Sean,

Sorry for the delay in our replying. For a quick lab test, try applying a reset pulse to see if the device gets enumerated. If not, we would need you to send protocol captures to analyze what is failing in the process.

Regards

0 Joel Jimenez0 over 8 years ago in reply to Joel Jimenez0

TI__Mastermind 18655 points

Sean,
Any update on this? Were you able to send protocol analyzer captures?
Regards

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TUSB2046B: Intermittent Issue with the USB Hub