FX3 Layout: Minimum PCB Layers requirment

[Anonymous]

I am laying out a new pcb for FX3 and was wondering if I could get away with 6 layers only, instead of 8 layers as used in the development kit? The reason for this is strictly cost reduction WITHOUT compromising data transfer speed and signal quality.

   

We are using the full 32-bit GPIF bus for communication between FX3 and a slave device, and there are hardly any unused pins (5 or less) on the 121-ball 0.8 mm FX3 IC.

       

Thanks

   

Mak

[Anonymous]

Please refer to AN70707 for hardware design guidelines related to FX3 family. Please note that the requirements in the AN70707 should be met strictly. If you meet those requirements, then you need not worry about the number of layers on the board.

   

http://www.cypress.com/documentation/application-notes/an70707-ez-usb-fx3-fx3s-hardware-design-guide...

[Anonymous]

Thanks Nishant.

   

I have another very specific question:

   

I have a board with two FX3 on it. The FX3 communicate with each other over a 32-bit parallel bus at 100MHz. Do i need a resistor on each data/clock line? I inherited the design from another guy who is not part of the team anymore and in his design he has a 33Ohm resistor on each data line as follows:

   

FX3(1) GPIO4 ---- 33Ohm ----- FX3(2)GPIO4

   

what is the purpose of this resistor and do I really need it? I am trying to reduce the board size and if I can do without this resistor, that will save me a lot of space.

   

Thanks

   

Mak

[Anonymous]

Yes, we recommend using 22-Ω series termination resistors to avoid reflection on the GPIF data lines (no need to put it on the clock)

[Anonymous]

Thanks Nishant. So as long as I have the series terminating resistors on 32 Bus lines I am  good.

   

What about the CTL0 to CTL12 lines? do they need terminating resistors as well?