Noise filters

[BellaX]

Hello,

the Pololu switcher does not have any input input filter to suppress differential mode noise.

This means you have to add it to your board design to be sure the switcher and the RPi noise does not
interfere with other instruments (radio, AIS, weather receiver) on your boat.

As far as i can see on your schematics you have no ferrite beads, no differential or common mode
filters, absolute nothing to suppress noise. At least you should have pads to add it if you find out
that you got problems with noise.

A simple way is to use power modules with proper design and a filter that is recommended for it.
For example from Wuerth Electronic. They offer a filter kit for every switcher module.

You can buy them directly from Wuerth and most of the times they are charging sample prices for
these small batches you are buying. And they offer a free of charge CE precompliance test of your
pcb! You really should consider that.

https://www.we-online.com/en/components/products/pm

Another way is to send the schematic to them and they suggest the parts with values and order numbers.
And of course you get the samples for free.

I am working with them for about 20 years and they are really nice and help you out if you are not
sure how to design switchers and filters to pass all the regulatory CE tests.

If you want i can do this for you. Wuerth Electronic is a big sponsor of our Maker-Space in Munich.

Best regards
Chris

[Sailoog]

Hello,

the Pololu switcher does not have any input input filter to suppress differential mode noise.

This means you have to add it to your board design to be sure the switcher and the RPi noise does not
interfere with other instruments (radio, AIS, weather receiver) on your boat.

As far as i can see on your schematics you have no ferrite beads, no differential or common mode
filters, absolute nothing to suppress noise. At least you should have pads to add it if you find out
that you got problems with noise.

A simple way is to use power modules with proper design and a filter that is recommended for it.
For example from Wuerth Electronic. They offer a filter kit for every switcher module.

You can buy them directly from Wuerth and most of the times they are charging sample prices for
these small batches you are buying. And they offer a free of charge CE precompliance test of your
pcb! You really should consider that.

https://www.we-online.com/en/components/products/pm

Another way is to send the schematic to them and they suggest the parts with values and order numbers.
And of course you get the samples for free.

I am working with them for about 20 years and they are really nice and help you out if you are not
sure how to design switchers and filters to pass all the regulatory CE tests.

If you want i can do this for you. Wuerth Electronic is a big sponsor of our Maker-Space in Munich.

Best regards
Chris

Thanks for that. We haven't had any noise issues in our tests, but let's see what happens in this round of testing. Anyway, we will take a look at your suggestion.

[Adrian]

the Pololu switcher does not have any input input filter to suppress differential mode noise.
[..]
A simple way is to use power modules with proper design and a filter that is recommended for it.
For example from Wuerth Electronic. They offer a filter kit for every switcher module.
[..]
I am working with them for about 20 years and they are really nice and help you out if you are not
sure how to design switchers and filters to pass all the regulatory CE tests.

If you want i can do this for you. Wuerth Electronic is a big sponsor of our Maker-Space in Munich.

Best regards
Chris

Hi Chris,

Thank you for your input! We went with the Pololu module to avoid designing our own switcher for this exact reason. But looking closer at the Pololu board, I think you are right and it doesn't include an input filter beyond the big input capacitors.

On the Wuerth website, I see that they suggest discrete LC low-pass filters as filtering solution for their DC/DC modules. Do you think that's also sufficient for the Pololu module (switching frequency 20-500 kHz according to their website), or did you have something else in mind?

If you have experience in this space, I'd be very interested in a collaboration. The Pololu module is kind of clumsy, but I didn't trust myself to put down a 3A switcher

Best Regards,
Adrian

[BellaX]

the Pololu switcher does not have any input input filter to suppress differential mode noise.
[..]
A simple way is to use power modules with proper design and a filter that is recommended for it.
For example from Wuerth Electronic. They offer a filter kit for every switcher module.
[..]
I am working with them for about 20 years and they are really nice and help you out if you are not
sure how to design switchers and filters to pass all the regulatory CE tests.

If you want i can do this for you. Wuerth Electronic is a big sponsor of our Maker-Space in Munich.

Best regards
Chris

If you have experience in this space, I'd be very interested in a collaboration. The Pololu module is kind of clumsy, but I didn't trust myself to put down a 3A switcher

Best Regards,
Adrian

Hi Adrian,

i am using switcher chips from LCSC/China. They are really cheap and they have the easy to solder SO-8 package.
The chips from Texas Instruments are way better and smaller but hard to get during the semiconductor shortage.

FR9855 0.2 EUR@100
3.3uH 0.1 EUR@50

Some capacitors for input and output and you are done for less than 1 EUR.

This is the schematic i am using:
   

And this is the layout:
   

For basic design of the input filter, you can follow this application note from Wuerth Electronic:
https://www.we-online.com/components/med...zed_EN.pdf

I will contact the sales representative from Wuerth tomorrow and ask for their recommendations. Maybe they can offer
a ready to use module that is cheaper than the Pololu one. If you are using the parts from them you can send your pcb
and they do the CE precompliance measurements for you. This is a service and you don´t have to pay for it! 

I don´t know the xmit power of the AIS. It may be a good idea to add a common mode choke to the 12 V input.
But let´s see what the specialist suggests!

Best regards,
Chris

[holgerw]

As i remember the Athur Power supply has an mode to powerdown the pi safely if the input power goes down...
This is an great pluspoint versus most powerbards. but i am not shure how this works without an big Condensator to hold the voltage.

.. we will see...

Greetings,
Holger

[BellaX]

I know the Pi 4 has some new additions to shut down. I am still using my proven circuit. I am using this for years without any problems.

   

The GPIOs are set to input and high impedance on every reset or standby of the cpu. This is the really last action of the cpu,
no code is executed beyond reset or standby commands. So it is impossible to get any data corruption.

Short explanation:
Triggered by pushbutton, the flipflip is set to Q high. #Q goes to low, the P-channel Mosfet is enabled and the Pi starts up.
The D input is set to GND so the next rising clock will 'move' this level to Q. After booting the GPIO for pwr off has to be set
to output and high.

If the cpu goes to power down, all GPIOs are set to input and high impedance. The mosfet is released and due to the pullup
a rising edge occurs on clock input. The flipflop is reset and the power cuts off. The second mosfet can be used to suppress
the rising edge. This is useful if you are connected remotely and you want to reboot without power off.

Of course you need permanent power for the flipflop but this is a few microamps only and you can get it from the 12 V input
using a simple voltage divider. If there is a RTC with battery backup this would work, too.

Cheers,
Chris

[Adrian]

As i remember the Athur Power supply has an mode to powerdown the pi safely if the input power goes down...
This is an great pluspoint versus most powerbards. but i am not shure how this  works without an big Condensator to hold the voltage.

.. we will see...

Greetings,
Holger

The MacArthur HAT uses a similar idea as Chris's circuit.

There's a switched 12V and permanent 12V connection to the HAT. See documentation for details on wiring.

The permanent 12V feeds the regulator that provides 5V to the Pi. When the switched 12V is turned off, the HAT sends a shutdown signal to the Pi. Once shutdown is complete, the HAT turns off the regulator which cuts power to the Pi. The regulator always stays connected to 12V, but uses less than 1mA while turned off.

[Sailoog]

Some background on this MacArthur HAT feature...

Some of you may have wondered why this power management is an optional feature:

- We want this HAT to be added to existing and new setups and there are already lots of OpenPlotter installations with its own power system.

- The premises of the MacArthur HAT are always "affordable" and "easy to manufacture" and with this external module you save money if you do not need to power your system and it makes manufacturing much easier.

- Separating elements ensure that the improvements or corrections of one part do not affect the other parts.

- These pololu modules are really efficient and well tested. Actually the PICAN-M board has been using the same module for quite some time and we are not aware of any problems with noise.

We have also done some tests with our own power modules but after the good result of the pololu module and in order not to delay the launch of the HAT any longer, we decided to use it and develop a power module calmly. Having someone with experience in this field is really great.

https://github.com/OpenMarine/MacArthur-HAT

[Jean-Marc Douroux]

Hello,

This assembly is a bit tight in input voltage. On a boat or car, you need a regulator circuit capable of withstanding 40V and more.
 There are big electrical pulses sometimes on the boat. With a regulator that only supports 18V, there is a real risk because the TVS diode with a threshold of 15V risks burning out, due to a lack of margin in relation to the voltage of certain alternators or chargers. There are also some chargers or MPPTs that have an equalization phase at more than 15V.
You really need a margin in input voltage with as much as possible an AEC-Q100 certified component.

Best regards

[Sailoog]

Hello,

This assembly is a bit tight in input voltage. On a boat or car, you need a regulator circuit capable of withstanding 40V and more.
 There are big electrical pulses sometimes on the boat. With a regulator that only supports 18V, there is a real risk because the TVS diode with a threshold of 15V risks burning out, due to a lack of margin in relation to the voltage of certain alternators or chargers. There are also some chargers or MPPTs that have an equalization phase at more than 15V.
You really need a margin in input voltage with as much as possible an AEC-Q100 certified component.

Best regards

Look at this test: https://forum.openmarine.net/showthread....2#pid25512