Alex_rcpilot
Member
Hi all, I'm trying to build this USB2.0 board with a cypress CY7C68013A in TQFP128 package. According to the datasheet, I have to use at least a four-layer board to ensure the performance. And then it gives several pieces of recommendations on how to handle this four-layer board.
The problem is, this USB2.0 stuff is the only thing that requires extremely high EMC standard, and that I don't think I will waste the whole board for this minor area. I want to use a two-layer board, and I don't expect too much quality loss, is it possible?
Here are the recommendations from the datasheet:
The following recommendations should be followed to ensure
reliable high-performance operation.
• At least a four-layer impedance controlled boards are required
to maintain signal quality.
• Specify impedance targets (ask your board vendor what
they can achieve).
• To control impedance, maintain trace widths and trace spacing.
• Minimize stubs to minimize reflected signals.
• Connections between the USB connector shell and signal
ground must be done near the USB connector.
• Bypass/flyback caps on VBus, near connector, are recommended.
• DPLUS and DMINUS trace lengths should be kept to within
2 mm of each other in length, with preferred length of
20–30 mm.
• Maintain a solid ground plane under the DPLUS and DMINUS
traces. Do not allow the plane to be split under these
traces.
• It is preferred is to have no vias placed on the DPLUS or
DMINUS trace routing.
• Isolate the DPLUS and DMINUS traces from all other signal
traces by no less than 10 mm.
If I use a two-layer board, will it be as simple as following EVERY BUT the first instruction? Thanks for your time.
The problem is, this USB2.0 stuff is the only thing that requires extremely high EMC standard, and that I don't think I will waste the whole board for this minor area. I want to use a two-layer board, and I don't expect too much quality loss, is it possible?
Here are the recommendations from the datasheet:
The following recommendations should be followed to ensure
reliable high-performance operation.
• At least a four-layer impedance controlled boards are required
to maintain signal quality.
• Specify impedance targets (ask your board vendor what
they can achieve).
• To control impedance, maintain trace widths and trace spacing.
• Minimize stubs to minimize reflected signals.
• Connections between the USB connector shell and signal
ground must be done near the USB connector.
• Bypass/flyback caps on VBus, near connector, are recommended.
• DPLUS and DMINUS trace lengths should be kept to within
2 mm of each other in length, with preferred length of
20–30 mm.
• Maintain a solid ground plane under the DPLUS and DMINUS
traces. Do not allow the plane to be split under these
traces.
• It is preferred is to have no vias placed on the DPLUS or
DMINUS trace routing.
• Isolate the DPLUS and DMINUS traces from all other signal
traces by no less than 10 mm.
If I use a two-layer board, will it be as simple as following EVERY BUT the first instruction? Thanks for your time.