24-bit delta-sigma ADC includes PGA
By Paul Rako, Technical Editor -- EDN, July 24, 2008
The Analog Devices’ AD7190 delta-sigma converter includes the functions to make a complete precision-measurement front end. In addition to the 24-bit converter, the part features a PGA (programmable-gain amplifier) configurable for gains of one to 128. The device also has an internal multiplexer to provide for two differential measurement sources or four pseudodifferential sources. It incorporates an internal clock source, a temperature sensor, and a bridge-power-down circuit to allow power savings by deactivating the bridge that the part is measuring. The high-precision converter, which can detect an open-sensor condition, suits use in strain gauges, scales, process measurement, control modules, scientific instrumentation and chromatography instruments, and other high-resolution data-acquisition tasks. Operating with 3 to 5.25V of power, the AD7190 consumes 6 mA of current; rms noise is 7 nV at a gain of 128. The offset drift is 5 nV/°C, and gain drift is 2 ppm/°C.
The device produces noise-free, 21-bit measurements at 4.7 Hz and 16.5-bit, noise-free measurements at 2.4 kHz, and it performs simultaneous 50- and 60-Hz rejection on an incoming signal. The ADC interfaces to the digital system using a SPI (serial-peripheral interface) or Microwire-compatible interface. You can select a no-latency mode to reduce software overhead if you need a valid conversion per output data. The device also has four general-purpose digital outputs, although two of these outputs also serve as alternative external reference inputs.
The AD7190 is available in a 24-pin TSSOP for a suggested retail price of $5.90 (1000). It operates over a −40 to +105°C temperature range. Samples are available now, and production quantities will be available in November. An evaluation kit interfaces to a PC with a USB.
