In my application I need to measure a voltage that is in the area of 50V, but my microcontroller has to be isolated from my power circuit. I came across the ACPL-C87A-000E IC. I followed the typical application circuit found in page 12 of the datasheet, but at first, I am not using an op amp. The circuit I am now using, converts the 50V to around 1.9V via a voltage divider, which is sent into the IC. This is my circuit:
By looking at figure 13 of the datasheet, page 9 (Vin vs Vout+,Vout-), I thought that I could send the 1.9V in the IC and by measuring just the Vout-, I could get a value that is proportional to the voltage measured (to be exact, in figure 13, Vout- and Vin seem to be inversely proportional). I left the Vout+ pin unconnected. Also, let me point out that all the voltage measurements are taken from digital multimeters.
However, there are some problems with the above-mentioned idea.
- Firstly, immediately after connecting the voltage divider's output voltage to the Vin of the IC, there seems to be a drop in that voltage (goes from 1.9V down to ~1.88V). The IC's Vout- value however seems to be correct for the given Vin, around the one expected from figure 13.
- Furthermore, the voltage divider's output voltage continues to change slowly, going from 1.84 to 1.89, as long as it is connected to the Vin of the IC. Obviously, the Vout- changes accordingly.
- After leaving the circuit on for some time, the voltage divider's output suddenly dropped significantly, to around 0.3 Volts, which I think may be the result of the IC going bad for some reason.
Another option I am considering for voltage measurement is the LTC6992-1, as suggested here. However, I don't know how to implement the last part, of measuring the PWM's duty cycle and converting it back to an analog voltage that can be read from my microcontroller. I am using a Beaglebone Black.
I would be really grateful for any other suggestions, perhaps simpler solutions, for measuring an isolated voltage with my microcontroller.