Power supply for FPGA  - Page 1
Forum section: electronics / general

author: joniengr081
author_rank: Regular Contributor
timestamp: December 15, 2022, 10:39:51 pm
content: Hi, I have searched and found that there are several options for the power supply for FPGA Kintex Ultra Scale. To find the optimum is a challenge. One option is to use step down buck converters and other option is to have several single channel buck converters. I appreciate if anyone come with a suggestion regarding selection of buck converters.

author: AndyC_772
author_rank: Super Contributor
timestamp: December 15, 2022, 11:32:28 pm
content: I would have said Enpirion, who did a fantastic range of fully integrated converters that were specifically designed for exactly this purpose.They were bought by Altera, who bought them for this very reason.They in turn were bought by Intel, who didn't care about that product line at all, tried and failed to sell it off, then discontinued it completely with no warning and no opportunity for a last time buy. Not that I'm bitter about that or anythingIf you find a suitable alternative - I know TI do something similar, but they're not available to buy last time I checked either - then do please let me know.

author: jayk
author_rank: Regular Contributor
timestamp: December 16, 2022, 12:11:31 am
content: There are lots of choices. Have a look at the Xilinx eval board designs. Googling 'ultrascale power supply' turned up a bunch of options. Also there's some helpful free tools out there (LTpowerCAD, LTpowerPlanner, TI webench). Xilinx UG583/UG1085 are helpful.Whichever way you go, be sure to pay attention to sequencing.

author: EverydayMuffin
author_rank: Regular Contributor
timestamp: December 16, 2022, 12:56:58 am
content: Monolithic Power Systems have a good selection and have done some Kintex US reference designs.https://www.monolithicpower.com/kintex-ultrascale-reference-designI believe you can upload your XPE file to their website and they will suggest parts.https://www.monolithicpower.com/contact/xilinx-xpe-file-upload.html

author: joniengr081
author_rank: Regular Contributor
timestamp: December 16, 2022, 06:59:29 am
content: How about Analog, Maxim and NXP. They also have dc-dc buck converters might be suitable for FPGA power supply. Any comments on these manufacturers ?

author: Someone
author_rank: Super Contributor
timestamp: December 16, 2022, 09:38:16 am
content: https://www.eevblog.com/forum/fpga/what-is-the-standard-procedure-to-design-the-power-delivery-network/Quote from: joniengr081 on December 16, 2022, 06:59:29 amThere are another dozen or so manufacturers you still have not mentioned, so possibly thousands of parts.... but still no mention of what you are actually looking for. Low cost? small size? high efficiency? multisource? input and output specifications?The manufacturer of the power chips is the least of your worries.

author: strahd_von_zarovich
author_rank: Contributor
timestamp: December 20, 2022, 07:09:02 am
content: Well, of course using modules which provide all the voltages you need is very tempting. However, when you can't buy them you are in very big trouble. I had to redesign FPGA boards because of chip shortage even if I used discrete components.However, If you use discrete components, at least you can produce them with small changes. So, use a regulator for 1V, and use another regulator for 3.3V for example, there are lots of options when you do this. You can use any voltage regulator which has enable, power good pins and enough performance(voltage tolerance, current capability, noise specifications).Try to find footprint compatible alternatives and try to use standard packages. Companies like Infenion produce very good regulators but their packages..., you can't find any alternative to them.Best regards.

author: luudee
author_rank: Frequent Contributor
timestamp: December 20, 2022, 08:59:54 am
content: I don't think there is a way around DC/DC converters for internal power rails of modern chips. I havejust finished a design where we needed both 0.8V and 1.0V, each roughly supplying 20A.The decision really boils down to:A. Use of the shelf modules+ easy to use+ pre-made, with all proper components- Expensive- Can be bulkyB. Design your own+ much cheaper+ more flexibility+ smaller, more compact- Must be very careful designing the circuit, read and follow the data sheet and app notes- PIA to select the proper components- PCB layout can be trickyMost use cases do not need PMBUS (and similar) programming interfaces. I usually stayaway from them, as the voltages in our application do not vary.If your project is small qtty, go with option A, if you will be doing mass production, I would recommendoption B. I also usually make a small test PCBs and evaluate my power supplies before making themain PCB with all the expensive components (e.g. FPGA).Good Luck !luudee

author: asmi
author_rank: Super Contributor
timestamp: December 20, 2022, 07:11:02 pm
content: That FPGA can consume tens of amps of current on it's Vccint rail, and if my memory serves me has ±3% regulation requirement over PVT. These are fairly strict requirements, so if you've never designed such high-current applications, you will be best served by first designing a small PCB just for this converter circuit, and you will be able to characterize it to confirm that it meets specifications.Also don't forget about heat management - 90% efficient circuit at 20A@1V will dissipate 2 watts of heat, there are usually several DC-DC converters on a typical FPGA board which also generate heat, and FPGA itself can get very toasty (even low-end Artix devices can get very hot and require a heatsink in certain scenarios - I've seen A35T heating up to over 60°C with a small heatsink!), so you have to make sure the board will not fry itself once you load it up and let it run for some time. Since high layer count PCB are still rather expensive, you will be hard-pressed to make your design as compact as possible, making heat management even more critical.

author: asmi
author_rank: Super Contributor
timestamp: December 20, 2022, 07:34:59 pm
content: Quote from: luudee on December 20, 2022, 08:59:54 amProgrammable devices can be useful for margining to increase precision of your regulation which will naturally vary board-to-board due to tolerances of components, or if you SoC supports multiple power modes (many high-end MCUs and a quite a bit of CPU SoCs support that).Quote from: luudee on December 20, 2022, 08:59:54 amUsing modules also tend to allow for more compact solutions because they typically take less PCB area then equivalent "discrete" converters, so if solution size matters to your design, modules are a way to go. They also tend to be better in terms of EMI.

author: luudee
author_rank: Frequent Contributor
timestamp: December 21, 2022, 03:12:56 am
content: Quote from: asmi on December 20, 2022, 07:34:59 pmIf you know what you are doing, you will be able to design proper supplies that exceedthe requirements, without having to "tune" your DC/DC converters. Imagine havingto tune 1000 PCBs, lolQuote from: asmi on December 20, 2022, 07:34:59 pmNonsense. Using discrete components you can usually make smaller DC/DC converters,unless they do vertical stacking, which is dangerous due to cooling issues.luudee

author: asmi
author_rank: Super Contributor
timestamp: December 21, 2022, 03:47:29 am
content: Quote from: luudee on December 21, 2022, 03:12:56 amNo amount of "knowing what you're doing" (nor arrogance displayed here) is going to defeat automatic voltage margining using system controller MCU. Not to mention having support for advanced power management modes with reduced voltage for lower-power modes.Quote from: luudee on December 21, 2022, 03:12:56 amNonsense if what you've just said, what I said is called "experience".

author: Someone
author_rank: Super Contributor
timestamp: December 21, 2022, 04:28:49 am
content: Quote from: asmi on December 21, 2022, 03:47:29 amForeign language collision?Voltage margin vs stability (phase) margin.Tight voltage requirements on new parts make it harder and harder to achieve without some active trim/calibration at least for static errors, programmable regulators are becoming the cheaper solution.Quote from: asmi on December 21, 2022, 03:47:29 amThe (surface mount) integrated power modules use the dense packing to increase operating frequencies, 3,4,5MHz and climbing which is impractical with discrete parts. Their power densities are hard to beat.

author: asmi
author_rank: Super Contributor
timestamp: December 21, 2022, 03:26:34 pm
content: Quote from: Someone on December 21, 2022, 04:28:49 amI was mostly using TI parts when I was beginning, so I tend to use their terminology. "Margining" is an ability to slightly adjust reference voltage (the range varies from part to part, but usually covers at least ±5%) and thus indirectly adjust output voltage, this is in contrast to programmable voltage, in which case you can set output voltage directly in a more-or-less wide range.Quote from: Someone on December 21, 2022, 04:28:49 amYeah, which incidentally often introduces a problem of having to deal with a lot of heat localized on a relatively small area.

author: joniengr081
author_rank: Regular Contributor
timestamp: December 22, 2022, 10:07:53 am
content: I was looking at the schematic of a development board which is Kintex UltraScale KCU105. I have attached a page for VCCINT which look like 40 A power supply. There are some questions. Is that a constant or transitional current in the beginning ?Can this DC-DC converter MAX15301 which they use for VCCINT can deliver that much current ? If we need to design a power supply for Kintex UltraScale then what are the options for VCCINT ? I mean which chips are recommended for that purpose.

author: luudee
author_rank: Frequent Contributor
timestamp: December 22, 2022, 02:41:46 pm
content: Quote from: joniengr081 on December 22, 2022, 10:07:53 amThe Max15301 is just a controller. It by itself, can not deliver 40A current. The external switching FETs, however, help it to provide high current.I constantly design high current DC/DC supplies like this one without the need for "tuning".luudee

author: joniengr081
author_rank: Regular Contributor
timestamp: December 22, 2022, 06:04:23 pm
content: Thanks for your reply. Then I think this chip supplies the gate current to the power FETs. I will try to find those in the schematic.

author: joniengr081
author_rank: Regular Contributor
timestamp: December 22, 2022, 10:36:32 pm
content: Hi,It's not easy to understand this power supply for VCCINT. The four FETs are rated around 30 A each but how are they connected is still a mystery to understand. These are N channel which means that when there is a positive voltage at the gate they will conduct. Two two FETs FDMS8018 are parallel and the other two FETs FDMS8558S are also parallel but then they are connected in series, two parallel on the top and then two parallel on the bottom. The Gate voltage are DL and DH. What is the function of them in MAX15301. How the 1V is produced and what is the function of DCRN and DCRP ?

author: langwadt
author_rank: Super Contributor
timestamp: December 23, 2022, 08:56:28 am
content: Quote from: joniengr081 on December 22, 2022, 10:36:32 pmit's a buck converterhttps://en.wikipedia.org/wiki/Buck_converter. The top fets are the switch, the bottom fets the "diode"DCRN and DCRP measures current via the voltage across the inductor or a current sense resistor

author: joniengr081
author_rank: Regular Contributor
timestamp: December 27, 2022, 05:49:12 pm
content: I have found that "VCCINT_FPGA" is actually is the power supply for VCCINT and VCCINT_IO Banks in the schematic of KCU105.

author: joniengr081
author_rank: Regular Contributor
timestamp: December 27, 2022, 06:08:09 pm
content: DH and DL are high and low side FET Gate Drivers but the four FETs: 2 x FDMS8018 and 2 x FDMS8558S are N-Channels, right ? I still refer to the same schematic in attachment.The output pins are OUTP (27) and OUTP (26). I don't understand how the output current is sensed on DCRN (31) and DCRP (30).VCC12_VCCINT is the power from main supply 12 V but how we get VCCINT ? Is that input supply ? if yes then where it is generated ?

author: joniengr081
author_rank: Regular Contributor
timestamp: December 27, 2022, 06:11:45 pm
content: I also don't understand about VCCINT_FET_SWITCH, is this switching ? if yes then where it is coming.

author: langwadt
author_rank: Super Contributor
timestamp: December 27, 2022, 07:43:42 pm
content: Quote from: joniengr081 on December 27, 2022, 06:11:45 pmit is the mid point between the two sets of fets, connected to the inductor L57

author: joniengr081
author_rank: Regular Contributor
timestamp: December 28, 2022, 11:10:00 am
content: Yes, it is connected to the inductor L57 but other than that it is not connected any other place, right ? I mean this is not driven at any other place.I also don't get the input supply to that chip. In addition to the 12 V, do we need to provide PWM signal as an input because it look like a switch

author: langwadt
author_rank: Super Contributor
timestamp: December 28, 2022, 12:09:06 pm
content: Quote from: joniengr081 on December 28, 2022, 11:10:00 amyou need to take about 20 steps back and start by learning how to read a schematic, what a buck converter is and then read the datasheet, your questions make no sense

author: luudee
author_rank: Frequent Contributor
timestamp: December 28, 2022, 12:29:00 pm
content: I recommend you look at the product page of the controller chip MAX15301:https://www.analog.com/en/products/max15301.htmlAnd also try to find some generic information how DC/DC Buck converters work: do a Google search for "Operational Theory of DC/DC Buck converters"Try to understand the underlying theory first, before jumping in to an advanced schematic. It is impossible to explain that in a couple of posts in a forum .Good Luck !luudee

author: joniengr081
author_rank: Regular Contributor
timestamp: December 29, 2022, 11:13:47 am
content: Hi, I have now studied how DC-DC buck converters works and I also have read the datasheet of MAX15301 again and found that the output voltage is set by a resister Rset at pin number 3. There 1 describe the resistor values and the output voltages.I also found that there is a SYNC pin number 1 at which switching frequency resistor has to be connected. In the section Setting Switching Frequency they have mentioned that "As a guideline, lower frequencies can be used to improve efficiency, while higher frequencies can be selected to reduce the physical size and value of the external filter inductor and capacitors." Is this true only for this chip or is true in general for switch mode DC-DC converters ?In the schematic of Xilinx KCU 105, they have used four FETs instead of two which is mentioned in the datasheet of MAX15301. I guess they did this to optimize the power supply for current up to 40 A then another question comes in my mind that how to test the power supply card ? I know that there exist a programmer "Maxim PowerTool MAXPOWERTOOL002# USB-to-PMBus" which can be bought separately to configure and monitor the chip MAX15301 through I2C in the power supply card but what about the load ? What kind of load can be connected at the output to test the power supply card for 1 V power supply delivering 40 A current ? which is like 40 Watt rating resistor

author: luudee
author_rank: Frequent Contributor
timestamp: December 29, 2022, 11:33:14 am
content: > "As a guideline, lower frequencies can be used to improve efficiency, while higher frequencies can be selected> to reduce the physical size and value of the external filter inductor and capacitors." Is this true only for this chip> or is true in general for switch mode DC-DC converters ?This is typically true for all DC/DC Buck converters.> What kind of load can be connected at the output to test the power supply card for 1 V power supply delivering> 40 A current ? which is like 40 Watt rating resistorTypically, people who design any type of power supply, use a "Electronic DC Load" for testing purposes.For example, I use IT8513C+ made by ITECH ...But you can also use a resistor. You can use plain copper wire to make a simple resistor for Power Supply testing.Have Fun !luudee