Author Topic: A7-FTG256: Decoupling caps on unused banks  (Read 1989 times)

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Offline rgc_Topic starter

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A7-FTG256: Decoupling caps on unused banks
« on: November 23, 2021, 11:25:02 am »
Hi folks,

I have an A7-FTG256 based design in which every penny and mm2 of board is relevant. I managed to get the IOs under 100, so I can make them fit in two banks out of the 3.5 banks in the package.

The UG483 indicates how to maximize ESD protection in unused banks, and so I did. What is not specified, and I just assumed, is that I can remove also the decoupling caps for the unused banks from the design.

Is this OK? anyone have done that already?

Thanks in advance.
 

Online asmi

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Re: A7-FTG256: Decoupling caps on unused banks
« Reply #1 on: November 23, 2021, 06:09:05 pm »
Yes you can.

Also, if you want to shave a bit more off PCB area and cost, you might want to consider using Spartan-7 instead of Artix-7. They are available in smaller 15x15 mm 196 ball package which has 100 I/O balls, so it should be a better fit for your needs. S7 has a bit less of DSPs that equivalent A7, but otherwise they are pretty much the same (sans MGTs of course, but FTG256 package doesn't bond out any, so it's a wash).

Offline rgc_Topic starter

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Re: A7-FTG256: Decoupling caps on unused banks
« Reply #2 on: November 24, 2021, 03:39:09 pm »
Thanks asmi, much appreciated.

Thanks for the heads-up on the S7, too. Unluckily (and strangely) there's no S35 part, and the design wouldn't fit on an S25. That makes the A35 the less expensive part available for the project.

 

Online NorthGuy

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Re: A7-FTG256: Decoupling caps on unused banks
« Reply #3 on: November 25, 2021, 05:12:14 am »
That makes the A35 the less expensive part available for the project.

How do you determine the price when it is not sold anywhere?
 

Offline rgc_Topic starter

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Re: A7-FTG256: Decoupling caps on unused banks
« Reply #4 on: November 26, 2021, 02:49:39 pm »
Distributors will usually give you a quotation, even when there's no stock. It is true that price ratio in between devices of the same family sometimes change, but I haven't seen too much of a change for the S7/A7 series in a few years, specially in high volumes where prices are nothing like in DK listings.

While that doesn't work for setting final product/contract pricings, it does work for picking up devices for new designs.
 

Online NorthGuy

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Re: A7-FTG256: Decoupling caps on unused banks
« Reply #5 on: November 26, 2021, 03:34:49 pm »
Distributors will usually give you a quotation, even when there's no stock.

The price is useless when there's no stock. The prices will be different when (if?) new stock emerges.
 

Offline rgc_Topic starter

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Re: A7-FTG256: Decoupling caps on unused banks
« Reply #6 on: November 27, 2021, 02:21:28 am »
Prices will most likely be different, but that is irrelevant for the device selection as long as all devices of a given brand/series are changed by a more-or-less similar %, and this is what happens in most cases in our experience.
 


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