Author Topic: SPI/Power Isolation  (Read 2535 times)

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Offline Lance

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SPI/Power Isolation
« on: August 06, 2012, 10:27:39 pm »
I'm working on a power monitoring system, and I'm trying to figure out how to go about isolating everything.

The current setup is to have multiple slave devices on modular boards (in case they get cooked) that communicate over SPI, that I want to isolate from the master.

For handling the SPI lines, I came across these digital isolators by Analog Devices:
http://www.analog.com/en/interface/digital-isolators/adum7440/products/product.html
Not necessarily that exact device.

What I'm trying to shop for now is isolation transformers to power the slave boards. Does anyone have any ideas on what's good to shop for?
#include "main.h"
//#include <killallhumans.h>
 

Offline PChi

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Re: SPI/Power Isolation
« Reply #1 on: August 07, 2012, 02:31:48 pm »
There are  number of DC / DC Converters with isolation available. I haven't any recent experience of any particular models or manufacturers though. An idea of the input and output voltages with output current requirements along with isolation specifications would help.
 

Offline digsys

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Re: SPI/Power Isolation
« Reply #2 on: August 07, 2012, 03:04:44 pm »
My common part I use for this sort of thing is - www.murata-ps.com/data/power/ncl/kdc_nme.pdf
There are several manufacturers that make a similar module.
For the data I use - www.silabs.com/Support Documents/TechnicalDocs/si844x.pdf
Awesome devices - low power (over entire data rate), high speed, high isolation. Similar to your find.
Both beat optos hands down.
Hello <tap> <tap> .. is this thing on?
 

Offline gxti

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Re: SPI/Power Isolation
« Reply #3 on: August 08, 2012, 12:58:03 am »
Dave did a video on this last week:

There's a whole category for them on Digi-Key if you need inspiration: http://www.digikey.com/product-search/en/power-supplies-board-mount/dc-dc-converters/4325599

For data I've also used the SI84 devices in the past, no complaints.
 

Offline Lance

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Re: SPI/Power Isolation
« Reply #4 on: August 08, 2012, 03:18:06 pm »
This looks like a pretty good way to go.

I really just need to power the slave micros that are doing the actual monitoring, so those are 5V or 3.3V (haven't settled on the model yet). In terms of the stuff I'm monitoring, the highest level is 28V as far as I know.

The big reason I want isolation is because this is connecting via RS232 to a rather expensive PC104 stack.
#include "main.h"
//#include <killallhumans.h>
 


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