ad7755 energy meter ic doubts

[raman00084]

while looking at the data sheet i am not clear that what ct should i must connect, are how much Milli volt / amp must be given to current sensing adc pin.


regards
kalyan

 

[schmitt trigger]

The information is outlined in the pin function description:

Pin 5, 6 V1P, V1N Analog Inputs for Channel 1 (Current Channel). These inputs are fully differential voltage inputs with
a maximum differential signal level of ±470 mV for specified operation. Channel 1 also has a PGA and
the gain selections are outlined in Table I.

Thus, once that you select a current transformer, then you would calculate a burden resistor that would provide that voltage at its maximum secondary current output.

Please bear in mind that ±470 mV is peak to peak, not RMS values. For a sinewave, that would mean 470/1.414 = 330mV RMS.
However, to properly measure distorted waveforms, I would calculate with a crest factor between 2 or 3. Which means that the RMS value should be 235 or perhaps 157 mV RMS.
Of course, if you employ the internal PGA with a gain different from 1, then the voltage must be scaled accordingly.


Also...do you realize that this chip is obsolete?

 

[raman00084]

thanks for the reply. for 1 amp current how much millivolt rms must be given to v1p.