I am using AD620 for measuring high side current.
AD620 supplies are +/-15V, Rg is 2.2K - gain ~23.5, input resistors of 1K and Vref is Ground.
The problem I am facing is above a common mode voltage of ~6.5V, the output voltage drops to zero. The differential input is 20mV.
Till the common mode voltage reaches 6.5V, the output is correctly differential input voltage X Gain.
I have replaced the AD620 with another, but the same results, though this 6.5V is at 6.3V. Two more AD620s also gave the same result. All these parts had a datecode of #1027, but an old AD620 with datecode of 9619 tested fine till about 12V Vcm. The reliability of the supplier of #1027 could not be established, so I ordered for some more from a different supplier, and, awaiting delivery.
In the meantime, I would appreciate if anyone had faced such problems, or if there is anything that I am missing.