Powering mote 24/7 using only a supercap and solar

[NeverDie]

@scalz said:

@NeverDie nope. just copper on bottom. ground return through your powerpad, in this case, can give less perf.

Are you using tented via's? Because otherwise, it looks as though your thermal pad is electrically connected to the "just copper" on the bottom. But I guess you're not referring to the "just copper" as "ground" because it's not being used as a return path per se? Looking at the "Recommended Layout" (Figure 34 on page 26 of the datasheet), I see it refers to a "Top BND" and a "Bottom GND."

At the moment I'm not sure what to do, so I changed from having almost the entire bottom connected to ground to just creating an equivalent thermal pad on the bottom that's the same size as on the top, which is electrically connected via the 5 via's. I haven't specified that the via's be electrically isolated from the top thermal pad, because in the TI diagram (which I posted above) it doesn't appear that they are.

[NeverDie]

Problem solved. Looking more closely at the datasheet's "recommended layout," regular oval pads should be fine:

So, no need to go exotic on the pad geometry. I can't tell from looking at it whether the thermal pad on the bottom is isolated from "bottom GND" or not, though.

[NeverDie]

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[NeverDie]

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[NeverDie]

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[NeverDie]

Here's what I'm going with for now:

As you can see, this one uses only one ground plane. Board size is 22mmx18mm. It uses 0603 and 0805 discrete parts, which for me makes it easier to hand solder. The only tricky part to hand solder will be the BQ25504 itself, but there's nothing I can do about that.

[scalz]

@NeverDie
sorry for delay..
i have a pad on bottom but it's not grounded on the bottom side. the power pad is grounded only on top. i don't remember but you should have a layout guideline included with the circuit footprint, for explaining.
i also use 0603/0805.

[NeverDie]

I guess my oval pads reverted to the default pattern when I re-synced with the schematic. So, fixing that again, here's what I'm going with:


There's a bit more clean-up I should probably do, but I need to learn a bit more about Diptrace before I can do it. Meanwhile, I sent Version 6 to the fab, since fabbing is the critical path.

[NeverDie]

@scalz said:

i also use 0603/0805.

In that case, if you want to post your fab files, I can post mine. Then we can have a healthy competition to see whether they work the same or whether one works better than the other.

[scalz]

@NeverDie
oh, no competition... or let me win please :laughing: I'm joking. that said i'm not sure, but I think i see Wally on your board ;)
I'm back in an hour for sharing. i need to assemble few boards for myself :)

[NeverDie]

@scalz said:

i'm not sure, but I think i see Wally on your board ;)

LOL. You probably need better ventilation when you're soldering. The fumes are getting to you. :laughing:

[NeverDie]

Interestingly, in today's mail I received the "BQ25504 Stripped" PCB

https://oshpark.com/shared_projects/CYdxpE9S

that I ordered on November 16. That's about twice faster than their normal turnaround speed when I send them new fab files. The board itself is noticeably smaller than the Tindie board.

[scalz]

@NeverDie said:

@scalz said:

i'm not sure, but I think i see Wally on your board ;)

LOL. You probably need better ventilation when you're soldering. The fumes are getting to you. :laughing:

:laughing: no fumes tonight, reflow oven working for me :)

Wally is in your GND pour, in each of your board I think.
I mean you should not have any gnd around some settings resistors and capa.
Check carefully the section 11.1 Layout Guidelines in datasheet.
This is why on the reference layout you see Top GND only on half board. Or then it may happen less performance depending of mutliple factors.
It's also explained how to route the GND.

That said, in case it can help, here is my gerbers https://www.dropbox.com/s/tugdbc3cfrlmdu7/bq25504_gerbers.rar?dl=0

Enjoy

[NeverDie]

@scalz

What is "Wally"? I haven't heard that term before, and it's not in the datasheet either. I thought you were jokingly making an obscure reference to Waldo, as in "Where's Waldo?" That's why I had thought the fumes must have gotten to you. I realize now that Wally must instead be a French electrical term of some kind.

[scalz]

@NeverDie
lol
yep you were right, where's waldo/wally but where i live we say Charlie :)

[NeverDie]

@scalz
Sacrébleu. I just now tried sending your gerber files to OSH PARK, but it complains, " I can't find a board outline file." A fab will need a complete set of files to get anything done.

[NeverDie]

In any event, the "stripped" BQ25504 board that I received yesterday looks rather disheveled:

@scalz
Do you see any Wally's in it?

[scalz]

@NeverDie
ahah :)

If it can help you, here it is : https://oshpark.com/shared_projects/XRsFBtzu
This is because i've generated the gerbers with an other fabhouse CAM.
In mine, GML is the dimension layer if i remember right.
You can also open the gerbers in a viewer like Gerbv etc..
For oshpark, i have modified it a little bit because of slightly different DRC.

[NeverDie]

@scalz
Thanks. I just now ordered it.

Interestingly, if you look at Ti's eval board for the bq25504, they do in fact connect the top and bottom ground planes, and the thermal pad on the BQ25504 is connected to the entire bottom ground plane, not just another small thermal pad:

https://www.ti.com/seclit/df/tidu094/tidu094.pdf

[scalz]

@NeverDie
cool.
Well, perhaps it's ok. I followed datasheet guidelines..no matter the powerpad is connected on top.

Perhaps, you may need the schematic to know where parts are placed ;)

You'll need to set your resistors of course.

If really needed, no problem i can upload all the files..