Question re: ADC and Sensor compatibility.

Other Hardware Sensors
1

Hi guys,

I have a basic question regarding the compatibility of a Tamura S22P hall-effect current transducer and a AD7753 energy monitoring chip. Specifically, I wonder if the use of the S22P is permissible if I use a voltage reference on the Channel 1 negative input.

To recap the two data sheets, the S22P produces a unipolar output, centered at 2.5V whereas the differential input into the AD7753 expects a bipolar signal with a range of 0V +/- 0.5V.

I was hoping to connect the S22P output to V1P (pin 4), while applying a series reference @ 2.5V to pin V1N (pin 5). Thus, the input would be 'floating' but the differential voltage would always stay in the proper range relative to the negative input. Is this permissible? I put an inquiry into Analog, but have yet to hear from them. For all I know, an engineer over there is still rolling on the floor laughing after reading my question.

In case this works, could I skip some of the suggested signal conditioning on the V1P signal? (i.e. 33nF cap, 1000Ohm resistor)

2

Would the best approach be to use a unipolar to bipolar converter as described here? The op-amp approach would also allow the output from the hall effect sensor to be tailored to the input of the ADC.

Or, as an alternative approach, use the LTSR-25, which offers access the to its reference output. This sensor would seem superior to the S22P for a bipolar input because the voltage coming out of an external series reference != reference voltage inside the S22P. With access to the reference voltage inside the LTSR25, one would always have a truely differential output.

The Analog statement inside the data sheet

"..the maximum signal level on analog inputs for V1P/V1N and V2P/ V2N is ±0.5 V with respect to AGND." (p.16 of datasheet)

suggests that the common-mode voltage has to be 0V. Thus, even if I use the LTSR-25, it would seem that a differential op-amp would have to return the signal to 0 +/- 0.5V to make it palatable for the AD7753?