AD8304: Measuring the resistance of textiles

Q

In case of electrostatic loadings, we need a negative Power supply of about
400V to drive the current through the resistor (textile), so that we have a
negative input current. Is it possible to use the AD8304 with negative current?

A

You need to measure currents in the range 40uA to 40pA, a dynamic range of some
6 decades.

In U.K. and Ireland we define conventional current as flowing from the positive
supply to the negative supply. In order for the AD8304 to operate correctly
conventional current must flow into the INPT pin. A +400V supply through the
resistance of the textile with the low side connected to INPT and VNEG
connected to a suitable negative supply ought to work in this case.

I recommend you spend some time thinking about over voltage protection too,
400V will kill the AD8302 quite dead so take to ensure INPT never sees a
voltage greater than the supplies.

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