This is very demanding... PIC32MX-DA for KiCad - Page 1
Forum section: electronics / general

author: technix
author_rank: Super Contributor
timestamp: October 29, 2018, 02:58:59 am
content: I kind of wish I can do this in 2 layers. I wonder should I float the EPAD or ground it?

author: Bassman59
author_rank: Super Contributor
timestamp: October 29, 2018, 03:02:51 am
content: Quote from: technix on October 29, 2018, 02:58:59 amWhat does the part data sheet say about how to connect the pad?

author: technix
author_rank: Super Contributor
timestamp: October 29, 2018, 03:05:29 am
content: Quote from: Bassman59 on October 29, 2018, 03:02:51 amNo mention at all.

author: ataradov
author_rank: Super Contributor
timestamp: October 29, 2018, 03:11:02 am
content: I always ground EPADs that have no specific recommendations by the manufacturer. I have never seen a part that did not have a ground or N/C on EPAD, so always grounding should be the safest option.

author: NorthGuy
author_rank: Super Contributor
timestamp: October 29, 2018, 03:51:40 am
content: Quote from: technix on October 29, 2018, 03:05:29 amMine says: "The metal plane at the bottom of the device is internally tied to VSS1V8 and should be connected to 1.8V ground externally"I guess this is about the pad.

author: technix
author_rank: Super Contributor
timestamp: October 29, 2018, 05:32:19 am
content: Quote from: NorthGuy on October 29, 2018, 03:51:40 amI didn't find that quote... Any indicator where that sentence is?

author: JPortici
author_rank: Super Contributor
timestamp: October 29, 2018, 08:18:33 am
content: Quote from: technix on October 29, 2018, 02:58:59 amI think that was one of their selling points

author: NorthGuy
author_rank: Super Contributor
timestamp: October 29, 2018, 02:05:16 pm
content: Quote from: technix on October 29, 2018, 05:32:19 amIn the datasheet. Your PDF viewer may have text search, then the fastest way to find it is to search. If not, it's immediately under the table which lists pinouts, among other notes. It is note #4.

author: technix
author_rank: Super Contributor
timestamp: October 29, 2018, 02:56:40 pm
content: Quote from: NorthGuy on October 29, 2018, 02:05:16 pmFound it, thanks.

author: Totoxa
author_rank: Newbie
timestamp: October 29, 2018, 05:52:47 pm
content: Quote from: technix on October 29, 2018, 02:58:59 amSorry for the offtopic, under what criteria did you group the pins on the symbol?

author: nctnico
author_rank: Super Contributor
timestamp: October 29, 2018, 06:01:28 pm
content: Quote from: ataradov on October 29, 2018, 03:11:02 amI have seen some special amplifiers from AD on which the epad is not connected to ground. Always reading the datasheet is the safest option.

author: Scrts
author_rank: Frequent Contributor
timestamp: October 29, 2018, 06:33:47 pm
content: Quote from: ataradov on October 29, 2018, 03:11:02 amJust FYI:https://www.st.com/resource/en/datasheet/vnd7140aj12.pdfAnd many other high-side drivers...

author: ataradov
author_rank: Super Contributor
timestamp: October 29, 2018, 06:36:06 pm
content: Quote from: Scrts on October 29, 2018, 06:33:47 pmAnd that's why I said only when manufacturer has no specific recommendations. All applications where is really-really matters, manufacturers are typically very explicit on what to do.

author: bson
author_rank: Unknown
timestamp: October 29, 2018, 08:25:14 pm
content: I would split it into functional sub units and focus on the functional schematic. Then look at the actual layout and see what it needs. But realistically I suspect the question isn't 2/4 layers but more like 4/6 vs board size. But it's impossible without seeing the rat's nest and how it fits in with mechanical aspects like connector or mounting hole placements. Also any other layout requirements you might have.

author: nctnico
author_rank: Super Contributor
timestamp: October 29, 2018, 08:47:56 pm
content: To do planning at the schematics entry stage it is better to draw components the way they are on the PCB. For a 100 pin part this is still very doable and it will help debugging as well. I'm pretty sure a 2 layer PBC is perfectly doable with some careful planning.

author: NorthGuy
author_rank: Super Contributor
timestamp: October 29, 2018, 09:32:12 pm
content: I used 169-pin BGA version. Even though I had 4-layer board, I had a ground plane and one of the layers was sparsely used, mostly for power (although I used it to fan out 2 pins). I managed to fan out all pins without problems. The layout is very friendly. Thus, there should be no problem with 2-layer fanout.If I were building a Linux board, I would go with 288-pin BGA version and external DDR2. This way, you get much more RAM. IMHO, doing this on 2-layers is possible, although you might need to sacrifice some of the pins.

author: technix
author_rank: Super Contributor
timestamp: October 30, 2018, 02:43:37 am
content: Quote from: NorthGuy on October 29, 2018, 09:32:12 pm32MB DRAM can work, especially if XIP is used for QSPI code storage to eliminate some code copying. External DRAM version get 128MB max but the board is much more complex.I don't really need all pins though, currently it is LCD, Ethernet, USB-OTG and I2C for now.