CMOS, 24-Bit Sigma-Delta, Signal Conditioning ADC with Matched RTD Excitation Currents
The part features one differential analog input and one single ended analog input as well as a differential reference input. Normally, one of the input channels will be used as the main channel with the second channel used as an auxiliary input to periodically measure a second voltage. It can be operated from a single supply (by tying the VSS pin to AGND) provided that the input signals on the analog inputs are more positive than -30 mV. By taking the VSS pin negative, the part can convert signals down to -VREF on its inputs. The part provides two current sources that can be used to provide excitation in three-wire and four-wire RTD configurations. The AD7711 thus performs all signal conditioning and conversion for a single or dual channel system.
The AD7711 is ideal for use in smart, microcontroller based systems. Gain settings, signal polarity, input channel selection and RTD current control can be configured in software using the bidirectional serial port. The AD7711 contains self-measurement calibration, system calibration and background calibration options and also allows the user to read and write the on-chip calibration registers.
CMOS construction ensures low power dissipation, and a software programmable power-down mode reduces the standby power consumption to only 7 mW typical. The part is available in a 24-pin, 0.3 inch wide, plastic and hermetic dual-in-line package (DIP) as well as a 24-lead small outline (SOIC) package.
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At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Transducer/Sensor Excitation and Measurement Techniques
(Analog Dialogue, Vol. 34, No. 5, August-September, 2000)
Ask the Applications Engineer-27: What problems am I most likely to run into...
(Analog Dialogue, Vol. 33, No. 2, February, 1999)
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