New family of ADCs offers best of both worlds, low power and low noise

Analog Devices today introduced a new family of sigma-delta analog-to-digital converters (ADCs) that deliver a low-noise and low-power solution for applications in industrial and medical instrumentation markets. The new ADCs feature both low noise (40 nVrms) and low power (400 uA), while offering a complete range of analog functions in less board area. This combination of features is ideal for applications where noise performance is critical, such as industrial process control and weigh scales, and space-constrained, low-power applications, such as portable instrumentation and medical equipment.

The AD779x family of analog-to-digital converters, which includes the AD7792 (16-bit), AD7793 (24-bit), AD7794 (24-bit), AD7798 (16-bit) and AD7799 (24-bit), deliver both low noise and low power. Operating with a 2.7-V to 5.25-V power supply, these converters consume only 400 uA. With noise of only 40 nVrms, they enable accurate measurements in power-sensitive applications. The output data rate from the devices is software programmable and can be varied from 4 Hz to 500 Hz. At 16.6 Hz they offer simultaneous rejection of 50 Hz and 60 Hz signals.

In addition to these performance advantages, the devices provide all of the functionality required for instrumentation applications, reducing design work and eliminating many external components. The AD779x data-converters include a high performance sigma-delta ADC, low-noise instrumentation programmable gain amplifier (PGA), multiplexer, current sources, clock, calibration registers, SPI interface, and a precision low-noise, low-drift reference (except the AD7798 and AD7799, which use an external reference for ratiometric measurements). Designers have the flexibility to turn off the internal reference, and use an external reference instead.

The PGA, multiplexer, excitation current sources, and input bias voltages allow the AD779x family to connect directly to sensors in myriad applications including PLC/DCS analog I/O measurement; temperature measurement using thermocouples, RTDs or thermistors; weigh scales; pressure and flow measurement; and general-purpose measurement equipment. For pressure and weigh scale applications, a low-side power switch is available to power down the bridge between conversions, minimizing system power consumption; the AD7799 features lower noise (30 nVrms) for these applications.

The AD7794 can accommodate six differential sensor channels, making it
ideal for the higher channel requirements of industrial and factory
PLC/DCS applications. The other parts in the family can accommodate
two or three differential channels.

The AD779x family of devices is sampling now and will be available in production quantities in November 2004. The AD7792 (16-bit), AD7793 (24-bit), AD7798 (16-bit) and AD7799 (24-bit) are available in 16-lead TSSOP (thin shrink small outline package), with prices ranging from $3.80 to $5.10 per unit in 1,000 piece quantities. The AD7794 (24-bit) is available in 24-lead TSSOP, and priced at $5.80 per unit in 1,000 piece quantities.

For more information, please visit:
To view the datasheet for the AD7794, click here.

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