XC7K325T Low cost Power management

[ehughes]

Sorry, putting a $0.50 power supply on an expensive FPGA is the dumbest idea ever.

That is like building a house on a foundation of toothpicks.

Don't give me this is "production/volume" nonsense.    There is no project that Uses a Kintex 7 that is a make/break because you need to save a couple dollars on a power supply.    Someone needs to reassess the economics of the project if you really need to use a shitty DC-DC converter to run a high end FPGA.     

[asmi]

Sorry, putting a $0.50 power supply on an expensive FPGA is the dumbest idea ever.

That is like building a house on a foundation of toothpicks.

I guess that "price is everything" mentality used for cheap crap from China is finding it's way into more expensive products. There is a number of chinese FPGA boards on Aliexpress with underpowered PDS. They can't seem to grasp a simple truth that "saving" a couple of bucks on PDS can end up ruining the whole project. And pretty much on all of those boards (that I've seen or read about) PDS has insane amount of switching noise that is way beyond the spec (the spec is <50 mVpp at 20 MHz BW limit for A7/S7, <30 mVpp for K7, <10 mVpp for MGT power rails). In my experience S7/A7 are not very picky about the noise (except for MGTs), but K7s are.
Another factor that is very commonly neglected is thermal regime. Take any of A100T "modules" that are aplenty on Aliexpress - vast majority of them have zero provisions for any kind of thermal control. The thing they don't realize (or just don't know) - when FPGA heats up, it consumes MORE current, exacerbating the heating problem. This can lead to a thermal runaway in come cases.

[SiliconWizard]

Agreed. Anyway, those big FPGAs are very power hungry and dissipate a lot of heat (at least if you use them as it makes sense to use them), and they are pretty expensive already. I don't really see the point of shaving off a dollar or two for what should be seen as the already upper-end of the series.

Underpowered - and without any proper thermal management - boards with big FPGAs are just deceptive items, close to scam IMO, as you won't be able to reliably use them for anything except the most trivial things (for which again it wouldn't make sense to use such FPGAs anyway.)

[OwO]

Yes but putting a $10 DC-DC module on without any thought is also careless design. If you do that here and there, it all adds up and you'll double your BOM cost. Not to mention those modules aren't always well designed and you will have to qualify them anyway. Experience gained in designing and troubleshooting your own DC-DC solution carry over to all future projects, and can save huge amounts in the long run. You don't want to be the designer that can't build anything and have to rely on pre-engineered solutions for everything.

I'm not going to go engineer my own 5A DC-DC solution because off-the-shelf chips do that well enough at reasonable price, but >10A and the value-add is large enough to justify in-housing it. It will be a project on its own, but if you design a lot of FPGA boards it's a worthwhile investment.

[OwO]

And uhh.. XC7A100T is a cheapie $10 FPGA. Those QMTech boards are overpriced for what they are, and I can tell they are designed hastily (there is no other reason you would use an expensive TI buck converter for 3A output). I will absolutely use a $0.5 power solution for a XC7A100T. I have no reason to believe that the JW5068A is any bit worse than what TI puts out, although I'd only trust it up to 6A because of power dissipation.

[ali_asadzadeh]

I think, I would first evaluate these chips to see what they can do, then If they pass the test, I will add them to the design.

[tszaboo]

                Δ
                |-------------------------------------------¬
Please read this part number somewhere here -----˩

And uhh.. XC7A100T is a cheapie $10 FPGA. Those QMTech boards are overpriced for what they are, and I can tell they are designed hastily (there is no other reason you would use an expensive TI buck converter for 3A output). I will absolutely use a $0.5 power solution for a XC7A100T. I have no reason to believe that the JW5068A is any bit worse than what TI puts out, although I'd only trust it up to 6A because of power dissipation.

[OwO]

I'm replying to the comment about A100T boards being inadequately designed, which are because it's a toy FPGA for playing around.

[SiliconWizard]

And uhh.. XC7A100T is a cheapie $10 FPGA.

I know you guys have incredible prices for Xilinx parts, but the current Digikey price is about 140 euros. I'm sure you can get better prices with high volumes and another distributor, but there's no way us poor europeans can get this for $10.

Oh, and for the XC7K325T that the OP was talking about, it's somewhere between $1000 and $2000 depending on package and quantities. For how much can you get them in China?

[olkipukki]

And uhh.. XC7A100T is a cheapie $10 FPGA.

10$ for XC7A100T ?? 
How much would XC7A35T cost then?

Where I can buy with a proper paperwork make sure these are not be nicked and okay to be (re)exported?

[olkipukki]

On the end of 2014, I bought first Artix-7 chips (XC7A35T-2FTG256C) for ~$36 that available only on Avnet. Eventually, the price has increased bit-by-bit and today a few bucks more in same quantity.

https://www.avnet.com/shop/us/products/xilinx/xc7a35t-2ftg256c-3074457345626042585/

You can buy these from LCSC for $17 (assuming they can supply required qty!)

https://lcsc.com/product-detail/CPLD-FPGA_XILINX_XC7A35T-2FTG256C_XC7A35T-2FTG256C_C181716.html

That's mean - 2 times (!!) cheaper, but not a magic 10+ times... 


Am I missing something? 

[olkipukki]

Buying from LCSC guarantees no fake or bad parts. It doesn't guarantee if it was not illegally imported or exported, nor guarantee if it was acquired from grey market. LCSC only guarantees the part is new, working and genuine, unless LCSC specifically identifies it as authorized distributor of brand X.

OK, understood, thanks

I can find XC7A100T cost $50 on LCSC, still better than 3 times compare to Avnet, but nothing close to $10 

https://lcsc.com/product-detail/CPLD-FPGA_XILINX-XC7A100T-2FGG484I_C410276.html

[TimCambridge]

I can find XC7A100T cost $50 on LCSC, still better than 3 times compare to Avnet, but nothing close to $10 

https://lcsc.com/product-detail/CPLD-FPGA_XILINX-XC7A100T-2FGG484I_C410276.html

And out of stock. LCSC have over 100 Xilinx parts, almost all with tiny inventories - only five parts with over 100 pieces in stock.

[OwO]

There are many stores selling the A100T around $10:

I've bought zynqs from one of these sellers before; they didn't have signs of reballing but are old stock and not in its original packaging. The date codes ranged from 2013 to 2018. The 2018 ones are unlikely to be salvaged at least, I haven't heard of devices with FPGAs get retired after a year. However you will definitely want to bake these before soldering. Salvaged A100T can be had for 40rmb if you can deal with the desoldering yourself.

[olkipukki]

And out of stock. LCSC have over 100 Xilinx parts, almost all with tiny inventories - only five parts with over 100 pieces in stock.

Not wonder, the most distributors have low FPGAs stock, and most stuff RFQ and 3+ months wait time.

Maybe LCSC can restock FPGA, never asked, but they definitely can do this for another components...

[OwO]

XC7K325T on LCSC shows 0 stocked but 140pcs sold in the past month. Most likely people are backordering. Similarly most "correctly priced" SMD capacitors are unstocked half the time, but still show lots of orders flowing. I've backordered chips from LCSC before (no FPGAs yet though) and was usually quoted 1 month lead time.

[ali_asadzadeh]

There are many stores selling the A100T around $10:

I've bought zynqs from one of these sellers before; they didn't have signs of reballing but are old stock and not in its original packaging. The date codes ranged from 2013 to 2018. The 2018 ones are unlikely to be salvaged at least, I haven't heard of devices with FPGAs get retired after a year. However you will definitely want to bake these before soldering. Salvaged A100T can be had for 40rmb if you can deal with the desoldering yourself.

Please share your good FPGA sellers in here(thier Taobao or other sites links), I have Chinese friends that will buy them for me directly from them