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Currently I am working on a small project using a Max10 FPGA from Intel.

I know about decoupling IC using a capacitor in parallel and a ferrite in series. This works for a small amount of VCC pins. But the FPGA IC has multiple VCC, VCCA and VCCIO pins. Which of the following ciruit ways would be the best to go with?

  • Use one ferrite for all pins and connect a capacitor after the ferrite to each pin.
  • Use three ferrites. One for VCC, one for VCCA and one for VCCIO. Connect a capacitor after the ferrite to each pin.
  • Use bypass capacitors only connected between VCC near the pin and GND.

Currently I would use the second solution, but I am not really sure.

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  • \$\begingroup\$ What does the appnotes say? what does the reference design show? TYPICALLY what I would do is 0402 (or 0201) of 1nF-10nF right at the via of a rail Ball. 100nF near the edge of the FPGA, 1uF + closer to the switcher to act as bulk. A ferrite to provide specific choking per-rail, with suitable damping \$\endgroup\$
    – JonRB
    Jul 6 at 10:27
  • \$\begingroup\$ Okay, so TYPICALLY you would use one ferrite for VCC, one for VCCA and one for VCCIO? \$\endgroup\$
    – F_Schmidt
    Jul 6 at 10:29
  • \$\begingroup\$ maybe ... I typically use an Igloo2 and I have one for the 3v3 (VCCIO and VPP) and one for the 1v2 (VDD) so it really comes down to what do you want to protect? \$\endgroup\$
    – JonRB
    Jul 6 at 12:19
  • \$\begingroup\$ Suggestions on passive components are not really precise. Each of the supplies will have a specific Power Supply Impedance vs Frequency demand, which you have to provide. While one of the rails could be happy with \$0.1 \Omega\$ impedance, another might need \$5 m\Omega\$. Once you know that, go simulate what you need (type and count of which caps, size and number of power planes). The manufacturers of the FPGA also offer tools for this, to include approximate parasitics, but Spice is probably more precise. \$\endgroup\$
    – tobalt
    Jul 6 at 12:32
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The holy user guide details all of the capacitors, ferrites and other filter means to be employed on the various rails. Luckily the Max10 has a lot of the required stuff on die so you can get off with a dozen of parts or so (I remember some spartan6 that required something like 60 capacitors of various size). Also many Max10 are single supply and that helps too…

I don't remember if it was for Intel/Altera or Xilinx/AMD but there was a 'power delivery network' tool to aid in the process.

If they say to use a 0402 package do not use a 0603 because it's easier to attach: the ESL is different and it is asking for troubles. If possible look at a reference design (i.e. a demo board).

Strictly related: be careful about power quality (i.e. noise); the enpirion converter they suggest are not cheap but many switcher do not reach the required level of cleaniness.

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    \$\begingroup\$ Altera has PDN tool in for of a excel sheet. \$\endgroup\$ Jul 6 at 12:50
  • \$\begingroup\$ That was the thing I was talking about! \$\endgroup\$ Jul 7 at 11:18

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