Hi Sir,

Our customer has found a divergence between ADE7880 EVB user guide (UG-356) Page.4 and AN-639 Page.3 about the formula of CT burden resistance calculation description as below:

[UG-356 P.4]

and [AN-639 P.3] :

UG-356 description is R1 = R2 = Ra = Rb = 1/2 x 0.5 / root(2) x N / IFS = y/x, where y = 1/2 x 0.5 / root(2), x = 1/(IFS/N),

so, Ra = Rb = y/x

but AN-639 description is **2**Rb = y/x;

Then, which one description is correct?

Thank you!

Hi Sam.S,

The equation from AN-639, sets up the burden in such a way so that the I max current corresponds to a half of full scale input. Use the equation of 2Rb = y/x as this will give some headroom for over current situations.

Best Regards,

Dlath