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September StudentZone Quiz Solution

Discussion created by bsiegel Employee on Sep 11, 2017

Question:

Please use a differential input for the AD8422, a gain of 100, a positive supply voltage of 15 V, and a negative supply voltage of –15 V. The reference voltage is 0. The common-mode voltage is 8 V. VDIFF ranges from 100 mV to 148.5 mV. Please assume for your research that we are using the full temperature range and a load of 10 kΩ. Using the diamond plot tool and the data sheet, please explain why this setup will not work.

Instrumentation Amplifier Diamond Plot Tool | Analog Devices 

Answer:

While the AD8422 is a rail-to-rail output instrumentation amplifier it is not completely reaching the +/- 15V as an output. As indicated in the datasheet the maximum voltage output over temperature is +Vs-0.25V and –Vs+0.25V for a typical load of 10kOhm. Therefore the maximum output voltage of the instrumentation amplifier is 14.75V and -14.75V, which is below the calculated output voltage of 14.8V. Therefore you will need to select a different amplifier or increase the voltage supply.

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