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USB Hosts Hubs Transceivers

OlEr_1999891
Contributor

Hi!

We are using CY7C65634 for an integrated hub function. However, we have experienced bad USB performance in certain scenarios such as streaming USB audio. When we by-passed the hub the problem disappeared. 

One theory is that the XIN clock signal is not good enough. Due to space constraints we couldn't use the large crystal from the reference design and instead we selected an SMD MEMS clock oscillator , ASEM1-12.000MHZ-LC-T. 

When we look at the XIN clock signal it doesn't look so good, see attached file. From -1V to 4.5V. 

Could you recommend a suitable clock or crystal CY7C65634  that has a small footprint / low height, ideally a SMD solution? Or if we go for a clock (not crystal), what parameters are important?

Cheers

Olof

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1 Solution
Sananya_14
Moderator
Moderator

Hi Olof,

The crystals we recommend are the ECS-120-20-4 from the DVK and NXE-970409 but the footprint may not be small enough for your application. For the clock oscillator, you could refer to SiT1602 and SiT8008 parts. Please refer to section 3.3 in the App Note for the parameters that need to be checked before selecting the oscillator. 

Best Regards,

Sananya

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3 Replies
Sananya_14
Moderator
Moderator

Hi Olof,

The crystals we recommend are the ECS-120-20-4 from the DVK and NXE-970409 but the footprint may not be small enough for your application. For the clock oscillator, you could refer to SiT1602 and SiT8008 parts. Please refer to section 3.3 in the App Note for the parameters that need to be checked before selecting the oscillator. 

Best Regards,

Sananya

View solution in original post

OlEr_1999891
Contributor

Hi Sananya!

We tried changing to SiT1602 and SiT8008 but the clock signal and result was the same. We believe that even if the entire clock signal looks a bit strange above and below 0V and 3.3V, it is good in the 0-3.3V interval and fits within the raise time interval required.

The problem we have is that when we stream USB Audio (and we believe it only happens in synchronous usb audio mode) there are notable errors in the audio output. For devices and OS that supports asynchronous usb audio it works fine, that is why we first thought is was a clock problem. We also seen problem with for instance USB camera connected to Android phones with bad video which looks like missing packets.

When we bypass the USB hub on the PCB everything works perfect so the clock (or whatever) problem is introduced in the hub IC and not in some other part of the system, e.g. interference.

The USB hub part of the schema is attached here, maybe you can see some problem there. Great if you have some ideas on how we can proceed here to find the problem.

Cheers

Olof

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Sananya_14
Moderator
Moderator

Hello Olof,

The schematic looks fine, I have no comments or suggestions for any changes. Could you please test with a HX2VL DVK if possible to check if the issue is related to the clock signals on your board? Please also let me know if the connected audio device operates in high speed mode or full speed mode. If it is a full speed device, kindly connect to a FS only port on the host if possible and let us know if the issue is still seen.

Best Regards,

Sananya

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