HD3SS3220: Pull down resistors on the Rx and Tx differential lines

prachi p

Part Number: HD3SS3220
Other Parts Discussed in Thread: 3220UFP-DGLEVM

Hi,

In the 3220UFP-DGLEVM INT027 schematics, there are 100K pull down resistors used on the TXp/n and RXp/n lines. There is a note saying "C1, C3, R10, R11, R6 and R7 are placed for interoperability purposes with USB Vcm above 2V."

In my design I am connecting the differential pair to a USB controller in place of a USB3.0 type A connector. I am not able to figure out if the pull down resistors are required. In the application note in the datasheet, the resistors are not used.

Please help me understand their functionality.

Regards,

Prachi

over 7 years ago

0 Luis Omar Moran over 7 years ago

TI__Genius 16150 points

Hello Prachi,

C1, C3, R10, R6 & R7 were placed in the HD3SS3220UFP-DGLEVM for interoperability cases, I mean, in some specific applications a higher voltage USB Vcm above 2V (up to 12V) is required, this is the reason these components were placed in the EVM. Basically, is depending of the application of the customer, in your case these components are not required.

Best Regards,
Luis Omar Moran
High Speed Interface
SWAT Team

0 prachi p over 7 years ago in reply to Luis Omar Moran

Intellectual 300 points

Hi Luis,

Thanks, that answers my doubt. Is there some application note or a document available which I may refers to for better understanding?

Regards,
Prachi

0 Luis Omar Moran over 7 years ago in reply to prachi p

TI__Genius 16150 points

Hi Prachi,

In my understanding there is not a document for this, please let me verify with the team.

Regards,
Luis

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HD3SS3220: Pull down resistors on the Rx and Tx differential lines