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ADI read-only ADCs simplify interfacing for data-acquisition apps

Posted: 02 Jan 2002 ?? ?Print Version ?Bookmark and Share

Keywords:analog devices? adi? adc? a/d converter ic? a/d conversion?

The AD7782 and AD7783 24-bit sigma-delta ADCs are read-only devices, simplifying interfacing for low-frequency measurement and low-power data acquisition applications. They are targeted at industrial applications, such as sensor, temperature, pressure and leakage measurement, as well as portable instrumentation applications.

Both converters tolerate high source impedance resulting from an on-chip differential input buffer, which permits high source resistance and capacitance without causing errors. Users can choose either low or high-level signal operation through a two-pin PGA, without having to change the voltage reference value.

The ADCs are complete analog front-ends for low-frequency measurement applications. The AD7782 has two differential input channels, while the AD7783 has one differential input channel and two matched 2005A current sources. The input channels on both converters are configurable with gains of 1 or 16, allowing full-scale input signal ranges of 12.56V or 1160mV from a 2.5V differential reference input.

The chips have a simple, read-only digital interface that can be operated in master mode or slave mode. There are no on-chip registers to be programmed. The input signal range and input channel selection are configured using two external pins.

The devices operate from a 32kHz crystal with an on-chip PLL generating the required internal operating frequency. The output data rate from the parts is fixed via the master clock at 20Hz and provides simultaneous 50Hz and 60Hz rejection at this update ratea peak-to-peak resolution of 18 bits can be obtained at this rate. They operate from a single 3V or 5V supply. At 3V, power dissipation is 2.85mW.

Both are housed in 16-lead SOICs and TSSOPs, with pricing at $5.10 for 1,000-piece quantities.

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