TUSB1044: Active Cable Usage Configuration for Thunderbolt Devices

Thanks Michael for the response. 

Are you aware of other redriver/retimer options that TI offers that may help facilitate this? I would very much appreciate any guidance you can provide. 

Thanks,
Matt

Hey Michael,

The TUSB1044 is spec'd to have a 10GHz -3dB bandwidth. This is the same bandwidth spec'd on the HD3SS0001 (www.ti.com/.../HD3SS0001), which is marketed as Thunderbolt switch. Is 10GHz bandwidth good enough for Thunderbolt on the switch but not on the redriver?

Justin

I don't mean to belabor the point, but the HD3SS0001 is called "Thunderbolt™ Technology Connector Source Selection Switch" or various permutation of that depending on where you look. It is included in the "Thunderbolt™ Powered by TI" selection guide (www.ti.com/.../index.shtml. On www.ti.com/thunderbolt, it is described as "The HD3SS0001 is a high-speed passive switch designed to support low speed and high speed signals required for ThunderboltTM applications .... The device supports 5.4Gbps for Display- Port and 10.3Gbps for Thunderbolt." So, I'm quite certain this device is intended for use in Thunderbolt designs.

If the 10GHz -3dB bandwidth on the TUSB1044 and HD3SS0001 is not sufficient for Thunderbolt (regardless of TI's marketing of the contrary), what would the appropriate bandwidth requirement be to support Thunderbolt?

Justin

Thunderbolt bandwidth is 10G, Thunderbolt 2 bandwidth is 20G, and Thunderbolt 3 bandwidth is 40G. HD3SS0001 supports Thunderbolt which means it supports 10G Thunderbolt. Thunderbolt 3 maintains backward compatibility with existing Thunderbolt technology, so if you plug Thunderbolt 3 into HD3SS0001, it drops back down to Thunderbolt 10G.

Thanks
David

Justin

TUSB1044 supports 10G Thunderbolt.

Thanks
David

Hey David,

Good to hear that the TUSB1044 support 10G Thunderbolt. We're trying to get this to work in an active cable application with Thunderbolt. Do you have some reference register settings which might work with short (~18") coaxial cables?

Justin

Justin

Do you have the insertion loss of the cable at 5G Nyquist frequency? You want to pick a equalizer setting that can compensate the insertion loss of the cable. If not, then it is best to look at the output eye diagram while sweep the equalizer setting.

Thanks
David

Hey David,

Unfortunately, the cables are uncontrolled by us so there is no single insertion loss number. The cables are provided and potentially changed by the customer, but will likely be very long relative to the USB spec and thus potentially have large insertion loss. The TUSB1044 re-driver is included in the design to mitigate the effects of such poor cables. We have tested with alt-mode spec-compliant USB-C cable with every possible equalizer setting, but have never been able to have Thunderbolt work. For Thunderbolt alt-mode, Is there a required directionality of the SuperSpeed lines that we must define for the TUSB1044?

Justin

Justin

TUSB1044 has no sense of Thunderbolt direction, as long as the DIR0/1, CTL0/1, FPLIP are set up correctly, TUSB1044 should work.

Have you tried a shorter cable and do you have a scope you can use to probe the signal lines?

Any chance I can take a look at your design?

Thanks
David