You can change the voltage level for that rail in software for overclocking/underclocking so if you just tied them together they’d be fighting each other. But if you did use an external regulator you could bypass that.
Now that I think about it this may be the reason phantom power isn’t an issue cause the leakage through the esd diodes would not power the core.
You’d hope so with the pi foundation
This approach has one downside, though, regarding power consumption.
I couldn’t find anything about the power draw in reset in the RP2040 datasheet. So I did some measurements myself. My raspberry pi pico, running the picoprobe firmware, draws ~22.7 mA when fully powered on, ~1.2–1.3 mA in reset and only 339 µA when the 3.3 V rail is disabled.
I can’t say how noticeable this difference would be in practice, though.
Shouldn’t it be 0 when it doesn’t get any power?
But yeah being held in reset will cause it to consume a little more power than completely disconnected from power. A whole ma seems like a bit much though but there is a lot going on on the pico.
On the raspberry pi pico there is a bit of circuitry before the voltage regulator. So the resistors and maybe even the regulator chip itself will still draw a little bit of power when the regulator is in the disabled state.
There is even an application note from the pi foundation on switching power to the rp2040 chip for low standby current applications.
Since you were going to power off the 3.3 it may be worth redoing your tests with an external 3.3v supply bypassing the built in regulator.
Pretty sure they were referring to stuff meant to run on a button cell for years not something like this.
But again, it is a tradeoff.
Still draws ~1.1 mA in reset mode when powered directly by 3.3 V. So no big difference there.
I’m wondering how much battery life this would cost me if the module is plugged in e.g. for a day. If it’s just a few minutes, I wouldn’t mind. But I don’t know enough about the battery side of things here to calculate that myself, or even just make a rough estimate.
Edit: Alright, according to DigiKey it’s just a simple division – leaving 5491 hours of runtime on the framework 16 from just this load. Meaning this will use about 0.4% of the battery life during one day.
For an estimated 5 h of battery life under medium use, this means about one minute less battery life. Which should be fine, I guess.
Assuming that my very crude calculations are correct 
.
5V * 0.0011A = 0.0055W, So it would discharge a 61Wh battery in just about 11k hours (ignoring conversion losses and stuff of course) XD.
Not 100% sure you divided the right things from each other there.
I divided the rated mAh value from the battery (which is btw. 85 Wh) by 1 mA. With 1.1 mA I get pretty much exactly 5000 hours.
Edit: Is the error here the conversion from battery voltage to the chip’s supply voltage?
Edit 2: Also, why did you use 5 V instead of 3.3 V for your calculation?
That only works if you are consuming the power at battery voltage directly. For stuff like this working with watts and watthours is much easier even if the conversions are never 100% efficient.
Yes, the pico would not be too happy with 18v and neither would most other usb devices XD.
There are all kinds of dc to dc conversions going on in a laptop, 5v rails for the usb, very high current ~1.3V for the cpu, 1.2V for the ram, 3.3v for internal devices and a bunch of other stuff.
Your picture looked like you were using an ldo for the 3.3v rail, on an ldo the input current is the same as the output current (it just burns off the voltage diff as heat) and the laptop is supplying 5v to the usb port.
That would be about right. Remember the oscillator is still going so there will be a certain percentage of the gates inside the chip still switching. If this is using a crystal it is certainly in the ball park I would expect.
This actually works remarkably well! Had to size down the voltage regulator, though, compared to the suggestion from the framework design files.
This is a 4-layer version, with ground pours and signal lines on the top and bottom and a ground and a 3.3 V plane internally.
The next step is now finding the right connector and switch for the final v1 design.
Yeah an ldo should do for most cases instead of the fancy switching regulator the pico uses.
4 layers probably makes the layout less of a pain. I made a very small rp2040 board once but I used 0805 components and soic8 flash so I could hand solder it and the routing got extremely cramped. I should probably figure out how to do layout on more than 2 layers at some point, especially since it got quite cheap now.
Edit: you may want to add at least some test-points for reset and bootsel for at least the one connected to usb, probably also for the other one and it’s usb lines.
That was already in the design, I just replaced it with a smaller footprint package.
Sure does, I really wouldn’t have wanted to route all the power on the front or bottom layer, too. Might not even have worked out in this case.
I’d say it’s pretty much the same as doing two layers. Doesn’t make much of a difference to me, at least.
Good point ^^.
My projects so far have all been hand soldered, too. Went down to 0604 components, that’s where the limit is for me with hand soldering. (I guess if I really had too, 0402 would also still be possible, but really painful ^^.)
This is the first project that requires me to go even smaller.
It certainly wasn’t easy but the board works. I did only need a few pins though so I was able to ditch a few components. the board was only about 1.5 rp2040s wide and about 3 or 4 long XD.
That’s great! I certainly have missed some very important connections before or had to make manual adjustments afterwards .
A sharp knife and good soldering skills are certainly very helpful in that case.
From my experience this really is something that needs time to learn and will get better and easier with each project. This is probably somewhere between the 10th and 15th board I designed.
If you want a really deep dive into PCB design, I can also highly recommend this video.
Four layers is the absolute minimum I would use for these sort of chips. Use of ground and power planes is essential to minimise power problems.
Kicad can do multiple layers quite easily, far more layers than you could dream about. It is quite easy to configure for this.
I have done multiple boards with the rp2040 on only 2 layers and all of them worked fine so far.
I don’t doubt it but I do have to do it XD.
Hi! I’m sorry if I’m not following the thread of conversation correctly, I’m new to this format.
I wanted to know if you’d made any progress with this.
I also wanted to point you to this device, the T-PicoC3, which has an RP2040 and an ESP32-C3 on the same board. They communicate via UART. It might be useful for you.
T-Pico C3 schematic
type or paste code here
Hi,
Thanks for asking!
I was basically ready to order the boards, but then realised that because of the size constraints there’s some extra cost (e.g. for smaller vias) I had missed and especially getting the parts placed is quite expensive. My previous projects I always soldered by hand, but that’s not possible with this.
As I’m currently just a student, I haven’t yet been able to afford that.
It’s actually not that expensive for a single board, but you have to order multiple and the parts placement has quite a high set-up fee regardless of how many boards you order. I believe it was about 200 € for 5 Boards overall.
If there’s a couple people interested in sharing the cost (and risk of it not working) and maybe get a working board out of it, I’d be happy to take care of all the work and share the design files with you so you can check them yourself. It’s just the financial side holding me back right now.
I will definitely post an update here if I find another solution.
That’s interesting, thanks for sharing!
If you’d be interested in selling them on Tindie and having someone look at the boards to double check they’re good, I’d be willing to fund the up-front cost.