Hi,
We are using AD627 amplifiers for force sensors (Wheatstone resistor bridge). In some cases we would like to exceed a gain of 1000, which is the maximum gain according to the amplifier's data sheet.
I have spent a long time trying to find an alternative part with higher maximum gain, but the only other suitable amp that I can find is the INA122 (max gain 10'000), which has considerably worse CMRR.
The amplifier must work on +9V single supply and provide a rail-to-rail output signal - ie. the highest output voltage should be less than 200 mV below supply.
Since there doesn't seem to be a better amplifier, I wonder what could happen if the specified maximum gain is exceeded on the AD627.
From the simplified schematic in the datasheet it doesn't seem like there would be a risk of damaging the device with a lower Rgain, or is there?
And yet, usually datasheet specs are there for a reason, so I'm wondering what it might be in this case...
I have tested the device with a gain of 2000, using 1 uF buffer capacitors at Vcc and the output (pins 7 and 6). It seems to work well, and the drive strength of the output is still good at gain 2000: with an 1kOhm load resistor, the output voltage drops from 9V to 8.2V, at a current of 8.29mA. For comparison, the same test with the INA122 makes the output voltage drop to 2.42 Volts, and I measure only 2.45mA current. Of course, in the final application, the amplifier only needs to drive a high-impedance load.
Any inputs on what problems to expect or what other scenarios to test will be greatly appreciated!
Thanks,
Martin