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Hack for single supply AD8553

Question asked by SaltMiner on Nov 16, 2016

I am looking to measure a 0 to 1 mA current through a 49.9 ohm shunt resistor.

 

I have a single +4.7V supply for the instrumentation amplifier (AD8553)and the ADC (ADC has external VREF).

My Gain for this IA is set to 50.

I have a buffered 3.300V reference as a VREF.

Based on the datasheet, I am thinking I can connect the high side of the shunt resistor (the power source for the current)

to the INN (pin 9) of the AD8553. Connect the load side of the resistor shunt to VINP pin 2.

I connect my common VREF between the ADC and the AD8553.

Now with 0ma across the shunt resistor, I get VREF out of the AD8553, which the ADC digitizes as full scale.

As my current goes up, my differential goes more negative, which means the VO is VREF - G*sensed voltage. So my ADC will read less than full scale. Just compensate my digital readings and I am in business.

 

Is this legit?

-Steve

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