3-Channel, Low Noise, Low Power, 20-Bit Σ-Δ ADC with On-Chip In-Amp and Reference

The AD7785 is a low power, low noise, complete analog front ends for high precision measurement applications. It contains a low noise 20-bit Σ-Δ ADC with three differential analog inputs. The on-chip, low noise instrumentation amplifier means that signals of small amplitude can be interfaced directly to the ADC. With a gain setting of 64, the rms noise is 40 nV when the update rate equals 4.17 Hz.

The device contains a precision low noise, low drift internal band gap reference and can also accept an external differential reference. Other on-chip features include programmable excitation current sources, burnout currents, and a bias voltage generator, the bias voltage generator being used to set the common-mode voltage of a channel to AVDD/2.

The device can be operated with either the internal clock or an external clock. The output data rate from the part is software-programmable and can be varied from 4.17 Hz to 470 Hz.

The part operates with a power supply from 2.7 V to 5.25 V. It consumes a current of 400 µA typical and is housed in 16-lead TSSOP packages.

APPLICATIONS

* Thermocouple measurements

* RTD measurements

* Thermistor measurements

* Gas analysis

* Industrial process control

* Instrumentation

* Portable instrumentation

* Blood analysis

* Smart transmitters

* Liquid/gas chromatography

* 6-digit DVM

* Up to 20 bits effective resolution

* RMS noise

* 40 nV @ 4.17 Hz

* 85 nV @ 16.7 Hz

* Current: 400 µA typ

* Power-down: 1 µA max