Question
Inquiry Description:Is it possible to feed nevative signals, relative to ground to the input of the on chip differential amplifier namely VINA+, VINA? .Or it is only possible to feed positive signals. I would need to input symmetrical signals relative to ground as a sinewave of +2V and -2V.In the datasheet absolute max ratings (table 4 and note1) it says -0.3 to +6.0V , but in datasheet it shows also to feed an input sinusoid of +/- 2.5 (fig,50, 52)
Answer
The details mentioned in the data sheet are correct.Please note that the values mentioned in the data sheet are the differential voltages(Vdiff=(V+)-(V-)). The inputs to the amplifier cannot exceedVdiff. (Vdiff is the supply going to the differential amplifier block=AVDD3)
The testing of the amplifier pins was done by shorting the inputs of the differential amplifier with the feedback components populated and the devicefully powered up. Vdiff was raised to 5.7V. There are input clamps which turn on at 3.2V internally and the circuitry involved internally are 5Vdevices and therefore 6V ratng is correct.
You could also connect one input to ground and the other to 5V. In general, as long as the AD7760 is fully powered with all the 5V and the 2.5Vsupplies then the absolute maximum ratings are correct.