This is my first post on this forum. I have a problem with an isolation amplifier and i hope there's someone here who can help me out.
Let me explain my situation. I use an ACPL-C79B from Avago to isolate measurement signals. At the input there's a AD8226 In-AMP, which buffers the measurement signal (0-60mV or 0-200mV) to the ACPL.
The power supply is 15V, but because i want to keep the input offset from the AD8226 as low as possible, i create a virtual ground. The virtual ground is created at 10V. So i have 15V to 10V = 5V positive voltage, and 0 to 10 = -10V negative voltage. It's shown below.
The ACPL is powered with the 5V positive voltage from this virtual ground (at the primary side). At the secondary side it is also powered with 5V, but from a floating power source.
The datasheet of the ACPL-C79B shows: 60mV input -> 0.5V output. When i use a new ACPL, the output voltage is exactly 0.5000. Perfect! But after a while, the output becomes 0,4860 (still 60mV input). I tried multiple chips (there not very cheap), they all give the same result after a while.
I can't find the problem. Please ask me, if there's something not clear.
(Because the ACPL creates a differential signal, the output voltage (0.5V) is Vout+ - Vout-. This is measured on the chip directly.) (The filter between the AD8226 and the ACPL is not used!)
Has anyone an idea, what causes the problem?
Could it be the virtual ground? Could it be the input signal? Because the - of the input is connected with the virtual ground.