HD3SS3220: LFPS Burst DC biased is around 0V

Tony Carter

Part Number: HD3SS3220

Our current Design has the HD3SS3220 in an UPF configuration like in the data sheet and is connected to a hub. Power and USB 2 is working but not getting any USB 3. When I looked at the LFPS polling signal at the connector it is biased around ground wich I don't think is correct. I looked at the signal going into the Hub and it is biased around ground also. I do not ave any capacitors on RX1 and RX2 pairs as the data sheet shows nor do I have any on the RX pairs going to the HUB. Is the lack of caps in the RX path causing the bias problem? Do I need to add caps either to the RX1 and RX2 pairs or do I just need to add caps in RX pair to the HUB?

Tony Carter

over 6 years ago

0 David (ASIC) Liu over 6 years ago

TI__Guru**** 179686 points

Tony

For UFP application, the capacitors on the RX path are optional since the capacitors are already populated on the corresponding DFP TX. If you do want to populate capacitors on the RX path, please populate the capacitors on RX1 and RX2 and capacitors values are 330nF.

Would you please share the HD3SS3220 portion of the schematic and the LFPS scope capture?

Thanks

David

0 Tony Carter over 6 years ago in reply to David (ASIC) Liu

Intellectual 360 points

David, here are the pages of the schematic with the HD3SS3220 portion and the HUB. Our scope decided to crap out and failed to boot yesterday so I dug out an old scope to capture the trace. I connected up an evaluation board of the HUB and the signal looked the same so I don't think this is our problem. I just wasn't expecting the signal going 380 mV below ground but it is withing the spec of part.

USB_page9.pdf HUB_page7.pdf