08-18-2016 07:32 AM
I once asked a question about designing the power supply for a zynq with DDR. i made a sketch of my power supply, because this is my first one, can anybody spot some rookie mistakes? just want to check if i didn't make any obvious mistakes.
greets, every help and tips are very appreciated
08-18-2016 07:53 AM
08-18-2016 07:59 AM
08-18-2016 10:37 PM
@rowesca From your power tree, looks like you are powering the PS & PL section of the Zynq from the same power supplies.
1. Did you use XPE to estimate the power you would be using for your design based on which you can choose the regulators current delivery?
I would suggest you use XPE before choosing your regulators to make sure you have enough juice to run your application.
2. You can also take a look at ZC702 schematics for the power tree as a reference. You don't need to follow it to the core, but will give you an idea of the power tree structure since you mention this is your first one and it will be good to have a reference.
Page 2 has the power tree of the board
3. You can also refer to Zybo board schematics which uses the same device as yours i.e. XC7Z010 to help you get started.
08-19-2016 11:15 AM
I would highly recommend using TI's Webbench software to analyze the load regulation with a large current step. Check the power estimate for your design and see what the supply will do when the load goes from the reported static current requirement to the full requirement (static + dynamic) for that voltage. I've noticed that some of the switching regulators from TI do a much better job with large load current swings than others. If the simulation shows too much voltage variance at the output of the supply, you'll need to make up for it by adding a lot of additional bulk capacitance to the bypass network.
08-23-2016 12:27 AM
can anybody spot some rookie mistakes?
You're using DC/DC converters to convert high input voltages to low output voltages (which gives a low duty cycle) without synchronous rectification. This results in poor power efficiency due to losses in the diode. If starting again, I recommend choosing DC/DC converters with "low side FETs" or "synchronous rectification" rather than using a Schottky "catch" diode.
The datasheets for those parts don't show efficiency curves for output voltages less than 3.3V, which should give you a hint as to their intended application(s).
Off the top of my head, the +1V rail converter would have an efficiency of about 60-70%, depending on which diode you chose. These days, at these power levels, if you're not hitting 90-95% you're either very cost constrained or you're not trying.
08-30-2016 08:53 AM - edited 08-30-2016 08:56 AM
By looking simple block diagram it is difficult to judge power supply design. Please note that FPGA power is not only depends upon device but also depends customer design (code)
Below are steps for selecting power supply for your design
1) Before design is ready download relevant device XPE spread sheet form the following link http://www.xilinx.com/products/technology/power/xpe.html
2) Then enter all planned resources in XPE spread sheets.
3) After completing resource and environmental entries XPE summary sheet shows approximate power consumptions of all power supply rails for your design . That help to select approximate power module/supply/regulators for your designs.
4) Once design is ready and implemented in Vivado, then use Vivado Power tool to estimate power more accurately. According to that fine tune your power supply loads.
5) Please note that you may use our evaluation boards as one of reference with respect to that particular designs. But the evaluation board are not meant for exact copying for all custom boards. Your design and board may have different load requirements