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.
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