How can I power my Arduino Nano 33 IoT?

Official Hardware Nano Family Nano 33 IoT
1

I'm preparing an embedded application for a Nano 33 IoT. I can't find any solid documentation about powering it.

First, how much current do I need to supply? The data sheet says the maximum power consumption is "TBC", but I don't know what that means. (I hope it's not "to be confirmed".)

The schematic indicates that there's an SJ4 jumper between the 3V3 pin and the output of the step-down converter IC. If I cut this, I could just apply 3V3 to that pin and be good to go, right? But I can't find SJ4 on my board to cut it.

The data sheet says I can supply -0.3 to 21 volts to Vin, but that doesn't seem to make sense to me. The back of the box says "4.5 - 21V INPUT - VIN". Is that to be trusted? Thing is, the website says "5 - 18V". Which is correct?

Supplying power at Vin would work for me but it means I'd need a 5-volt supply to run the step-down converter on the Nano board and then a 3.3-volt supply to run my off-board circuitry. I was hoping to have a simple design with only one voltage rail.

If I supply Vin, I can also use the 3v3 pin as an output. How much current can it source? Looks like the MP2322 data sheet says it will output up to 1 amp, but I don't know how much the board needs and therefore don't know what balance is available at the 3v3 pin for my off-board circuitry.

There are a few other threads on this subject, all closed with no definitive answer. Some say it's okay to back-feed the on-board converter, others say the board will be damaged.

Am I just looking in the wrong place for documentation?

2

Wow, where to begin?
Most datasheets will discuss powering options.
I will not address each of your points, as most are wrong, and the easiest way to fix that is to get you on the right track.
IF you see conflicting min/max voltages, use the most conservative as too high will kill the board and too low will not allow proper operation.
Current is drawn or pulled, you don't 'provide' it other than you need a PSU capable of the max power the board will use where power is Volts times Amps. MOST MCUs need less than 1 or 2 amps so even a battery can work for some amount of time depending....
Cutting traces on a new board is just silly. Why would you think that?
One rule is to NEVER use the board as a power supply. You need one supply for the board and one for the 'other' stuff. YES, it can be a single wall wart or battery, but the positive terminal of the supply must have two wires, one to the VIN of the board and the other to any sensors, motors, etc. NOTE: look up using capacitors to filter noise and decouple, that common voltage lead will inject noise from the motor to the board with possibly troublesome consequences.

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"One rule is to NEVER use the board as a power supply."

That's 7805 thinking. The IoT's DC-DC converter has much more capability in this regard.

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Yes, but for the less experienced, it's a handy Rule Of Thumb to keep them out of trouble.

5

You won't
Hopefully, someone who has actually used one will see your post and offer some advise.

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That's what I expect, too. But it doesn't seem to be the case for the Nano 33 IoT.

Here's what the "Power Consumption" section says:

PowerConsumption
PowerConsumption995×157 12 KB

As you can see, the minimums are negative voltages which doesn't make much sense. And the "maximum consumption" is "TBC", which I'm afraid means "to be confirmed".

Do you have access to a corrected datasheet that you can share with the community?

Well, I guess it's because the schematic shows this jumper, which would disconnect the output of the converter circuit from the 3V3 supply on the rest of the board, but leave the 3V3 pin connected to its bus.

SJ4 Jumper
SJ4 Jumper651×319 16.7 KB

Wouldn't you agree that, with SJ4 opened, the the converter is isolated from the 3v3 rail and the board can be safely powered from an external source on the 3V3 pin?

That's a curious point. I think it's safe to use power from the board's on-board regulator, as long as that external draw doesn't exceed the amount of current the on-board regulator can supply in excess of the needs of the boards itself.

Another diagram in the data sheet is shown here:

PowerTree
PowerTree923×873 24.4 KB

This diagram shows 600 milliamps available for "user application". Does the data sheet support your rule?

Oddly, there's a green dot in the legend for "voltage range" which isn't used anywhere in the diagram.

But the grey boxes are I/O pins, including +3V3. Is the "1A max current" designation telling me I can draw a maximum of one amp from this pin? I doubt that, since the MP2322 can deliver exactly that much current as a maximum, per its data sheet, and wouldn't have enough to power the Nano itself. Does it mean I can externally source one amp here to power the board externally?

The sum of the on-board components is 365 milliamps, which leaves about 635 milliamps headroom to the 1 amp maximum of the MP2322. Maybe the 600 milliamp limit for "user application" makes sense, then but given all the other errors in the data sheet (search the data sheet for "lorem ipsum"), I might need a bit of convincing to latch on to any particular interpretation of these numbers.

And that's why I'm asking here.

This demands a complicated design, and I'd like to avoid that complexity if possible.

7

Just use VIN.
The DC-DC is 3.3V (it's not 5V, lest there be any confusion).

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1A is the total (964.65 to be exact). 600 is the total available, but each pin is only seven ma.
The power tree is ONE document that shows you that you can power the board by USB OR VIN. The voltage range is a function of the regulator; I would assume 7 or 8 is safe (2 x 18650 LiIon), but the limit is 21V (that would make the VR VERY hot)
I am not sure what your problem is, but I have given you lots of pointers. Now tuning out, good luck.

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Could do, but that means I need an external 5-volt supply. Since the board can't accept more than 3.3 volts on any input (and any output will be with 3.3 volts high), I need to have another 3.3-volt supply for my external logic.

Or, level-shift every input and output.

Or, find solid documentation about how much current I can take out of the 3v3 pin while still powering the Nano and use that current to run my off-board circuit.

And so my "problem" is that I'm still trying to figure out if the board can be powered externally by 3.3 volts on the 3v3 pin. The documentation isn't clear on that. Nor is it particularly convincing on the 600 milliamp supply availability on that same pin. And there are conflicting answers here the forum.

If I can supply the board 3.3 volts on the 3v3 pin, then I don't need a second supply rail and I don't have to worry about level conversion. I can just design a 3.3-volt power supply to run the board and my external logic and I'm good to go.

Sorry if this wasn't clear from my original post.

10

No.

I believe the 600mA is sound.
How much do you need ?

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Why are you ignoring the arduino.cc website with the following info on the page. Here is the interesting part in pic1. You can supply 5V (up to 21V) on VIN. Now the board is supplied. From that same 5V source run another lead no level converters needed to whatever 5V stuff you have. Documentation is VERY clear, where were you looking?
BTW, 600ma TOTAL, BUT only 7ma PER PIN!
LINK

Screenshot 2025-02-24 at 17.27.17
Screenshot 2025-02-24 at 17.27.17708×298 10.7 KB

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The 600mA figure is for the DC-DC converter's output.
I haven't read anything that indicated 5V is needed (peripherals, offboard, etc)

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Sorry, I read where he said

I need an external 5-volt supply
, which did not mean what I thought, he later clarified everything is 3.3V. So, as long as he can run all his outboard stuff with 7ma, he is good to go.

14

The 5V is sufficient to run the "IoT" and - provided all of your external circuitry is 3.3V and that current budget is not > 600mA - everything should be fine.

Whatever happened to that?

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I'm not done with my design yet, but I think I'll be under 500 mA. If it's safe to rely on the Nano's on-board regulator for that, then I should be fine.

I took a flyer and powered the board from the 3v3 pin with 3.3 volts from my bench power supply and it worked fine. I don't feel so comfortable about backfeeding the converter. It's a pity the board doesn't match the schematic, because cutting that pad to isolate the converter would have been a great solution.

Thanks for helping me reason it out!

16

You shouldn't - it's a bad idea to do that.

You could do a load test on the DC-DC (470ohms, >2W) - to prove that out.

17

Since it is an IoT - if you turn on the radio then you'll have to take that into account, deduct that from what's available for everything else.

18

I wait for someone who has actually used one to join the discussion

19

I have.

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Then I guess you are the expert!