I have a Spartan 6 FPGA (XC6SLX9-2TQG144) and I'm designing a power supply for it.
Let's assume that I will utilize all of its logic (very possible) and I want to clock it as fast as possible (around 350MHz).
How can I estimate the power (number of amps) that my PSU has to supply? Not precisely, but just an order of magnitude. 1.2 V for core and how many amps? 3 A? 5 A?
Side question: is sequencing of power supplies neccessary for this Spartan?
If your design is not a big commercial thing, I would be tempted to suggest not reinventing the wheel and go with a tried and tested design - especially if you are not sure yet about how the overall design will look
The Papilio Pro board uses the same Spartan 6 FPGA, and its schematic is open source:
(Image from here)
In the past I've successfully replicated the power supply design for a project did at university - and that involved HDMI so was fairly high frequency.
What I can tell you now is that you won't be using all the FPGA resources, it is almost impossible to do that in a realistic design mainly because there are more logic resources than routing resources. Furthermore as you start getting to usage levels higher than 80% you quickly find your design can't run as fast because of competition on routing resources - stuff gets further away so the fmax goes down.
You will also have an incredibly hard time getting a design to run at 350MHz when the global clock tree is only capable of at most 375MHz. The logic will have to be incredibly well pipelined, combinational paths kept to the bare minimum (e.g. no logic functions > 5 input most likely). You'll also have to design it in a way that areas of logic clump together well. Probably even having to physically specify where in the chip stuff goes. For a really complex design I am using an FPGA with an maximum clock frequency of 780MHz, but because of the size of the design and logic complexity, it can barely do the 250MHz I need (271MHz fmax from timing analysis).
You should download and use Xiinx' power estimation tool. With it you specify the various IOs, logic used, clock speeds, et cetera, and spits out an estimate.
It is here:
You should absolutely worry about power sequencing... at least until you read the documentation and it tells you that sequencing is not required. In previous generations sequencing was more of a concern, but according to Xilinx DS162 "Spartan-6 devices do not have a required power-on sequence". Worry about ramp rates (DS162 Table 6), and sequencing in relation to other start-up critical components in your design. For example if your FPGA starts configuration before the voltage rail on the configuration flash comes up, nobody's going to be happy.
You can copy other designs, but ultimately there is no substitute for reading and understanding as much documentation as you can.
