I recently received samples of the RCV 420 and was messing around with one the other day. I followed this guide: http://www.ti.com/lit/an/sboa023/sboa023.pdf
This is a guide detailing how to use the chip with a single supply. This works by varying the reference "ground" and keeping the high terminal constant. I found this setup has an odd behavior however. For my setup I used the exact setup in that schematic except my current source is replaced by a potentiometer. I am powering it (and generating the current through the resistor) with a single +24V.
Everything seems to work fine, 4 mA yields 0V output and 20 mA 5V (and everything in between). The odd behavior comes when you disconnect the +24 supply for the entire circuit (including the current source). Upon plugging the thing back in, the chip now outputs the incorrect voltage. For example I give an input current of 15 mA and I get an output of about 3.45 V. Now if I disconnect the supply for everything, upon plugging it back in (with 15 mA once again flowing) I get a voltage now of 2.02 V ????
I don't understand why this is happening, is it something to do with the way the ref pins are connected? The thing I found that fixes this, is if I disconnect the current source and then plug it back in. Upon doing this I find that the voltage output is now once again correct. This strange thing happens for any current (however the output voltage is different based on the what current you do it with). So why is this happening?
