nrf5340 schematic variations

[mej7000]

In the reference layouts for the nrf5340 there are four variations. I can see the subtle variations in each, but don't know I why would choose 1 vs 2 vs 3 vs 4...  Is there a document which describes the merits of each of the four options? 

nsscprodmedia.blob.core.windows.net/.../nrf5340-xxaa-reference-layout-1_2.zip

The reasoning for not using a ready-made module:
We are creating a device requiring strict consistency over time (requiring an oscillator with low (<3)ppm?), essentially creating a high quality stopwatch, which maintains accurate time in both active and sleep states. We will have a number of these devices that will initially sync their clocks and it's important that they don't excessively drift, without constant "re-syncing".

Therefore we believe we need to have control over the oscillator hardware. However, I am open to alternative ideas if the idea is incorrect.

We initially anticipated using a module, but the 32Mhz clock is always integrated. We could find modules without 32.768khz clocks already in place.

These devices are all monitoring sensors and each device will report it's own time, but each device's time must in sync with the others.

Client insists that each device have it's own internal clock as opposed to a parent device that gets a flag from the children. Communication between devices is wireless/shockburst

[mej7000]

mathiaso said:

That should work. Just remember that everything communicating with the nRF5340, e.g., sensors, external flash, etc., has to have the same voltage as the nRF5340. Thus, if you have different voltages from the two bucks, the things communicating with the nRF5340 have to be supplied by the same buck as the nRF5340.

Thanks! This is huge, because no, I hadn't thought that all the way through! I will run everything off of Buck1 at 3v0. My understanding is that 3v0 will give me lower power consumption on the 5340 than a lower voltage would, which makes sense. All the other components on the PCB will run on 3v0.

Thanks for breaking out what each induction pair does! I didn't realize how that worked although now that I reread that section it makes sense.

mathiaso said:

Correct. Although, it is up to you if you are going to use the high voltage mode or not.

Since I am regulating the entire circuit to 3v0. I seem to have the option to use Normal or High Voltage mode. Can you see a benefit to using one over the other in this case?

Thanks again!

[mathiaso]

mej7000 said:

Thanks! This is huge, because no, I hadn't thought that all the way through! I will run everything off of Buck1 at 3v0. My understanding is that 3v0 will give me lower power consumption on the 5340 than a lower voltage would, which makes sense. All the other components on the PCB will run on 3v0.

Thanks for breaking out what each induction pair does! I didn't realize how that worked although now that I reread that section it makes sense.

You're welcome!

Also, remember that you have to set the DC/DC registers high in your code to actually enable the DC/DC regulators.

mej7000 said:

I seem to have the option to use Normal or High Voltage mode. Can you see a benefit to using one over the other in this case?

In high voltage mode, you can supply external circuitry from the VDD pin.

mej7000 said:

powering anything through the nrf5340 VDD/VDDH... Could you elaborate a bit on what you mean by this?

This is what I was referring to:

"External circuitry supply

In high voltage mode, the output from VREGH can be used to supply external circuitry from the VDD pin.

As illustrated in High voltage mode, external circuitry can be powered from the VDD pin"

But you weren't going to do that, based on your previous comment?

And btw, to get an idea of your power consumption, the Online Power Profiler may come in handy.

[mej7000]

mathiaso said:

Also, remember that you have to set the DC/DC registers high in your code to actually enable the DC/DC regulators

Is there a good sample to review for setting the DC/DC registers with Zephyr?

mathiaso said:

In high voltage mode, you can supply external circuitry from the VDD pin.

I see why this confused me... I saw the block diagram for the Normal Voltage Mode and assumed the VDD was always a supply voltage to the processor. Now I see how VDD in High Voltage Mode can be a regulated "Vout" when the config registers are set and the inductor/capacitor pair is in place... I'm used to seeing VDD always being the label for the supply on other processors and I made assumptions... (If I still don't have that correct please let me know)

So, if I've got that right then I wouldn't be using VDD as a regulated supply. I would just use Buck1 at 3v0.

I checked out the Power Profiler. Does Normal vs High Voltage Mode affect the overall power usage? If not, I assume Normal would be the right Mode to choose.

[mathiaso]

mej7000 said:

Is there a good sample to review for setting the DC/DC registers with Zephyr?

You simply set this in your prj.conf file. Have a look at the answer provided in this case.

Have a look here to find further descriptions of the configs.

mej7000 said:

I checked out the Power Profiler. Does Normal vs High Voltage Mode affect the overall power usage? If not, I assume Normal would be the right Mode to choose.

There is minimal difference between Normal and High voltage modes when used similarly, so the Normal voltage mode should work fine.

If you want added flexibility, it is possible to do what is mentioned in the answer to this case, adding a switch that makes it possible to connect VDDH and VDD.