Part Number: TUSB1002
We have the TUSB1002 EVM evaluation board to test how TUSB1002 works. We observed:
1) when it is loaded with Sumsung portable SSD it can work in USB3.0 with MODE F. I can measure the around 5Gbps 1-0 patterns in Tx/Rx after plug in the cable. But when it is in MODE 1 the HOST cannot identify the SSD.
2) when it is loaded with SanDisk portable SSD it only work in USB2.0 with MODE F. I can measure the around 50Mbps 1-0 patterns in Tx/Rx after plug in the cable. But when it is in MODE 1 the HOST cannot identify the SSD.
So my questions are:
1) Why loaded with different SSD it behaves different as USB3.0 and USB2.0 respectively.
2) How HOST identify the device in USB3.0? By sending "Handshake" package with 1-0 patterns? Are the 5Gbps and 50Mbps 1-0 patterns "Handshake" patterns? But the data rate is different.
3) How HOST identify the device in USB2.0? By continuing sending 1-0 patterns? We didn't catch any "Handshake" patterns on Channel D+/D- in measurement.
4) Will HOST with USB2.0 and USB3.0 detect the device simultaneously? Or HOST detect USB3.0 first and see if the device support USB3.0, if not it will detect for USB2.0?
The reason is that some devices (SanDisk SSDs included) have a compatibility issue when detecting the TUSB1002 RX terminations, we already have a workaround but it has not been updated to the reference design (the new EVM units will include this fix). the workaround is to include 265nF AC coupling capacitors between the RX terminations and the USB connector. It has been successfully tested without compromising the device´s performance.
In reply to Diego Cortes:
Thanks for your reply. I illustrate the workaround as the figure below with a 265nF AC cap between EQ RX and USB connector. Is it correct? Another question is that usually the SanDisk itself has AC coupling capacitor at its own output port, so can you please show me why another 265nF AC cap is needed here?
In reply to Shuai Jin:
We followed your suggestion to add AC caps between RX of EQ and SanDisk SSD on the evaluation board. But it still works in USB2.0 instead of USB3.0. The device is SanDisck Extreme 900 Portable SSD. Can you plz give me more details to have the evaluation board functioning in USB3.0 with this SanDisck portable SSD?
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