TUSB501: AC decoupling capacitors placement in USB3 redriver when using proprietary storage device

E M

Part Number: TUSB501

Tool/software:

Hello,

I have a board with a USB3 host and it is connected to a proprietary storage device, and I want to have the TUSB501 redriver between them.

I have two questions about the matter:

The storage device already has ac decoupling capacitors in series on its TX lines, so I was asked not to put my own capacitors. However, since I am using a redriver, do I need to put capacitors after the redriver anyway?
In other words, if I connect the storage device TX lines to the redriver RX pins, do I need to place series capacitors on the TX pins of the redriver?
The storage device does not have capacitors on their RX lines, so it is my responsibility to do so.
My question is, do I need to place capacitors before and after the redriver, or just after?
In other words - my host TX lines connect to the RX pins of the redriver, and the TX pins of the redriver connects to the RX pins of the storage device. Where do I put my capacitors?

Thank you very much.

5 months ago

+1 Vishesh Pithadiya 5 months ago

TI__Mastermind 38275 points

Hi,

Please have a look at the schematic for the TUSB501 EVM. This will cover your questions:

0 E M 5 months ago in reply to Vishesh Pithadiya

Prodigy 30 points

Hi,

Thank you for your answer.

This schematic did indeed cover my second question, however my first question remains.

If the EVM more matched more situation, there would be capacitors in series to the R3, R4 resitors. So in this case, would you put capacitors on pins 6,7 of the redriver as well?

Thank you.

+1 Vishesh Pithadiya 5 months ago in reply to E M

TI__Mastermind 38275 points

Hi,

Do you know what values the AC coupling capacitors are on the storage device?

The USB bus is required to be AC coupled, so the EVM design is under the impression there will be a 100nF cap on the TX lines connected to the RX pins. The USB3.x bus capacitance must be between 75nF and 265nF.

Yes if there is a capacitor present on pins 2 and 3, you will still need a capacitor on pins 6 and 7.

0 E M 5 months ago in reply to Vishesh Pithadiya

Prodigy 30 points

Hi Vishesh,

The values of the capacitors the manufacturer placed are 100nF, which fits the range you provided.

So what I understand from you is that I still need to place capacitors after the redriver (on it's TX pins), even though there are capacitors already on the RX pins. Understood, I'll do that.

Thank you very much.

0 Vishesh Pithadiya 5 months ago in reply to E M

TI__Mastermind 38275 points

No problem.

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TUSB501: AC decoupling capacitors placement in USB3 redriver when using proprietary storage device