Solar charge controller + STM32 + sensors +LoRa - how to separate the boards?

[I14R10]

Hello

I'm trying to integrate a LiPo solar charge controller (CN3791) , LiPo battery, STM32G030 series microcontroller and temperature and humidity sensors. I'm wondering what's the best way to separate those items and if I should separate them on different boards. Regarding noise from switching solar charge controller.

My current thinking is that I should separate the boards like this: linear voltage regulator + STM + sensors + LoRa (RFM98) on one board, and battery + solar charge IC + its inductor, capacitors, mosfet etc on another board, connected with pin headers.

What I want to avoid is switching noise from solar charge controller going into STM or even worse, sensors. I don't know how bad that switching noise is, I've read the datasheet for CN3791 and followed all PCB layout guides regarding switching noise, but it still feels wrong to have it put right next to other components. Am I overthinking? Can I put them all on one board and just separate digital from switching stuff?

I don't have a lot of experience in this, so any advice is welcome. And, side note, smaller size is a plus. I don't want to have 10x10cm board with items separated very far away.

 

[KlausST]

Hi,

Put all on one PCB.

I´m doing industrial designs, (switching 6000A RMS in 1 foot distance), switching regulator on board and still got about 15 bit precision on the on board ADC. No metal case around.

On another PCB I´ve a step down, a capacitive negative supply, a microcontroller, USB, .... OPAMPS, ADCs.
I detect input signals in the range of 30pA. (X-ray measurement).

.. just to show that it´s possible.


***
I guess you don´t need this high precision.
So use a PCB, use a true solid GND plane (yes: true solid). (.. to begin with. with more experience you may add dedicated cuts)
* Keep an eye on the GND currents.
* proper power supply bypassing
* proper signal conditioning with filters
* if possible use one common clock source
* ...

Just draw the complete schematic.
Then do all the parts placement on the PCB (no routing so far)
Then show us.

Klaus

 

[I14R10]

Klaus, thanks for the reply. I did as you suggested. The PCB looks like this: Left top is RFM98 LoRa module, top right connector is solar input, Right side is solar charge controller, lower right is battery output. Battery should be glued on the back side of the board and should fit within the white frame. Lowest part of the board are TMP117 and SHTC3 sensors. There are 2 "bridges" without copper to reduce any potential heat transfer to the part with the sensors.

PCB shape might be weird, but I like doing something weird instead of square PCB only. I'll probably change the shape so don't pay attention to it.

And here's the schematic

 

[KlausST]

Hi,

Doesn't look bad.
Batt_adc should get a capacitor close to the microcontroller.
Also VRef.

There isn't much sensitive analog circuitry. Why are you worried?

Klaus

 

[I14R10]

Hi,

Doesn't look bad.
Batt_adc should get a capacitor close to the microcontroller.
Also VRef.

There isn't much sensitive analog circuitry. Why are you worried?

Klaus

Yes, I forgot that capacitor.

I don't know. I was thinking about that 300kHz frequency from charge controller spreading onto maybe I2C lines. Or getting into RFM98 LoRa although it's mostly in transmit mode...
I just wanted to check if I'm missing something obvious.

 

[KlausST]

Hi,

Keep the noisy lines short.
Keep the sensitive lines short.
In best case route them in 90° angle against each other.

But don't worry there is no big risk for problems.

Klaus