TUSB551: the drive ability after the device. And whether we can use two devices in cascade.

Hi Frank,

Can you elaborate on what the customer means by "drive ability"? Are you referring to the allowable amount of trace after TUSB551? What is the application here? What is the pre and post channel length in this application? 

HI Malik,

There are 8inch trave + Cable 610mm + Connector *6 behind the TUSB551 device. We want to check how many distance the device can support?( if include the connector, how to evaluate the risks?) 

Thanks.

Hi Frank,

The distance supported depending on the impedance profile and insertion loss of each component and connector. The quality of the source will also play a factor. In this application I believe multiple re-driver will be needed. The USB source should have some layout recommendation guidelines, the first re-driver should be placed at near this recommendation. One redriver should be placed near each connector. One redriver in this case does not seem to be enough. Could you also describe the "switch node" in this system? What is the end equipment? 

Hi Malik,

i have highlight the SW( switch node-- between the LEFT Ear 1410A04D connector and 1422A07T (ExaMax 6x8) connector) on the table above( yesterday post), it's switch board. The EE is blade server. How many db our device can compensate?

Thanks.

Hi Frank,

TUSB551 has ~9 dB of equalization (max) and ~-6 dB of de-emphasis (max), this correlates to about 17 inches at 4 mil pre-channel and 11 inches at 4 mil post-channel. This assumes a completely straight trace with no bends, vias or additional components in the path. 

FAQ on pre-channel vs post-channel:

Note: The de-emphasis/pre-emphasis of the signal source and equalization of the signal receiver at the far should also be taken into account when determining placement of the redriver. Asa general rule of thumb FR4 has an insertion loss of about 0.49/inch at 2.5 GHz (5Gbps) assuming a completely straight trace with no bends, vias or additional components in the path (best case).

Hi Malik,

many thanks. it seems we can put several TUSB551 cascade in the line, correct? We ask the question is because for some link, the links cannot accept the cascade structure. Thanks. 

hi Malik,

could you please help check it? If we have the test data of cascade application, it should be better. Thanks.

Hi Frank,

Could you give more details on this issue? What is the test setup? How many redrivers are cascaded? What device is having issues? Is there a USB data log describing what you are seeing?  

Hi Malik,

For the customer also consider other supplier solutions, which mentioned the cascade may have the issue for USB3.0 link. I also don't have too much experience abut it. If we have seen some other customers use the cascade structure before. The customer will have no concerns any more. Many thanks.

Hi Frank,

We have done functional test in a cascade configuration with this device and found no issue. For any electrical test (i.e. far-end eye diagram) the results would look the same since TUSB551 is a limited redriver (output eye is independent of input eye even in cascade configuration). Previous test eye diagrams can be found in the datasheet in section 7.10 Typical Characteristics and 9.2.1.3 Application Performance Plot. 

Could you give more details on this issue? What is the test setup? How many redrivers are cascaded? What device is having issues? Is there a USB data log describing what you are seeing?  

Hi Malik,

The customer's concern is the link may not be up when power on and off many times. We have two redrivers cascade. If we have done the test before. Can we provide the test setup about the board? Whether we can do the on/off test many times to see whether the link is ok? Many thanks.

Frank

Hi Frank,

You can do this kind of test with TUSB551. Customer will have to ensure that both redriver are powered up with similar timing. Is the customer trying to use the EVM and needs help setting up the test?

Hi Malik,

We cannot find 551 EVM on TI website. Could you please help do the test? Many thanks. 

Hi Frank,

As I mentioned testing this would require more specific information from the customer on the application. What kind of result is the customer looking for here (i.e. eye diagram)? Has the customer tried some test and is seeing issues?

HI Malik,

Two sockets in cascade.  Do Hotswap and power up/down repeat to see whether the link failure( the usb status  or eye diagram). The customer just has the concerns. If we have some successful story in other customer side with cascade structure feel free to let us know. Thanks,

Hi Frank, 

Sorry for the delay. I am still trying to find resource to test. Speaking with other engineers it has been tested before and no issues were seen. Behavior will vary with USB Host and Device connected. I recommend customer to try and test on there side with a prototype to confirm behavior. 

Closing thread, moving to internal email.