Hi,
I have a circuit which I need to measure the RMS value of two AC signals with up to 33VAC peak and 400Hz. I am using two LTC1966. My power supply is single 3.3V. My AC signals dont have DC and swings from +V to -V.
At first, I used the connection like figure 9b of datasheet with single ended AC coupling and resistor voltage divider at IN2. I got correct readings, but when I connected the two AC signals at same time I got a short circuit, because of common ground.
Than I changed to differential input (schematic below), but the readings are unstable. When I connect the AC "GND" to DC GND I got correct measures, but I cant do it, will come back to first problem.
Could you guide me to a solution and tell me what I am doing wrong? At LTspice simulation my circuit works.
It is very urgent, for a new product, please help.
Thanks in advance.