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I'm working on an device that will switch a load and measure the energy of said load. This is for a 120/240VAC system. I plan on using the MCP39F511A for this job.

However in their datasheet and evaluation board they put the current shunt on the low side (neutral, after the load), but in my case I can only measure from the high side (before the load).

Can I measure from the high-side using the same topology ?

Here's a link to the datasheet

Here's the typical application :

enter image description here

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    \$\begingroup\$ If all the off-board connections are opto-isolated, and you only have one phase to worry about, then I'd say there's no real difference between L and N or high side and low side anyway. It makes a lot of sense to "ground" your circuit next to the shunt. \$\endgroup\$
    – tomnexus
    Dec 7, 2022 at 4:34
  • \$\begingroup\$ It might be safer to use an isolated CT or Hall device. And there might be a problem with 220 VAC and the voltage dividers for voltage reading. They should be fully differential. \$\endgroup\$
    – PStechPaul
    Dec 7, 2022 at 11:10
  • \$\begingroup\$ @PStechPaul Components values will be adjusted for the working voltage, I'm only using the application example as a visualisation. \$\endgroup\$
    – GmodCake
    Dec 7, 2022 at 15:39
  • \$\begingroup\$ @tomnexus this is a completely enclosed product, the rest of the circuit is also completely isolated from the mains. This bit (the MCP39F511A) will be powered via an isolated DC/DC module, I could plug the L to the 0V of the DC/DC and it would be fine, correct ? \$\endgroup\$
    – GmodCake
    Dec 12, 2022 at 22:47
  • \$\begingroup\$ Yes - but read your country's safety rules. In my opinion there is no difference between L and N anyway. You can't rely on N being close to ground because it can and often will be connected backwards. So if you have a hard constraint about where you can put the shunt, then just connect the whole monitoring circuit as you wish. You still need to test the PCB and opto isolation barrier for the many-kV impulses you get on the mains. \$\endgroup\$
    – tomnexus
    Dec 13, 2022 at 7:01

1 Answer 1

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On page 4 in the absolute maximum ratings, it states:

"Analog Inputs (I+,I-,V+,V-) w.r.t. AGND ...................-2V to +2V"

Im not 100% on this but I would advice against it, Since your potential on the high side is much higher than AGND.

EDIT: Considering tomnexu's comment: you might get away with it by reversing all connections to L/N (shunt to high side, DGND to L, V1+ to N), but playing around with Line Voltage is never a good idea.

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