ADE7878 input range/protection

Document created by analog-archivist Employee on Feb 23, 2016Last modified by analog-archivist Employee on Feb 23, 2016
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I am using an ADE7878 to build an  energy meter: the unit must comply with
EN62052-21 (IEC 62023-21) and I need your help about this  point: the meter
shall be able to carry  for 0,5 sec a current equal 20 Imax. This  means that
at the input (IAP, IAN, IBP, IBN, ICP, ICN) of ADE7878 we will have a +-0,5V x
20 = +-10V for 0,5  sec. The absolute maximum rating of  ADE7878 is +-2V. I had
a look at the  reference design for smart meter (that is supposed to comply
with standards) but I did not see any particular hardware  to protect the chip.
It seems to be quite difficult and expensive to clamp all  current inputs to
+-2V: is this done  internally of ADE7878?

 

There is no internal protection against these overvoltages. You need to place
diodes to protect not only the current inputs ((IAP, IAN, IBP, IBN, ICP, ICN,
INP, INN), but also the voltage inputs (VAP, VBP, VCP and VN).

We do not have any example for the ADE7878, but have for ADE7913, with isolated
ADC. This IC has the same ADC structure and the protection that we used on its
voltage inputs on the evaluation board should be similar to the one you should
use on all ADC inputs of the ADE7878. Refer to ADE7913 evaluation board
schematic at ADE7913 page on our website.
Basically the V1P from the schematic is VAP of the ADE7878. The VM is the VN of
the ADE7878. The same structure should be applied to IAP and IAN pins of the
ADE7878.
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