AD7722

The AD7722 is a complete low power, 16-bit, sigma-delta ADC. The part operates from a +5 V supply and accepts a differential input voltage range of 0 V to +2.5 V or ±1.25 V centered around a common-mode bias. The AD7722 provides 16-bit performance for input bandwidths up to 90.625 kHz.The part provides data at an output word rate of 195.3 kHz.

The analog input of AD7722 is continuously sampled by an analog modula-tor eliminating the need for external sample-and-hold circuitry.The modulator output is processed by two Finite Impulse Response (FIR) digital filters in series. The on-chip filtering reduces the external antialias requirements to first order, in most cases. The group delay for the filter is 215.5 s, while the settling time for a step input is 431 s. The sample rate, filter corner frequency, and output word rate are set by an external clock that is nominally 12.5 MHz. Use of a single bit DAC in the modulator guarantees excellent linearity and dc accuracy. Endpoint accuracy is ensured by on-chip calibration.

This calibration procedure minimizes the zero-scale and full-scale errors.Conversion data is provided at the output register through a flexible serial port or a parallel port. This offers 3-wire, high speed interfacing to digital signal processors. The serial interface operates in an internal clocking (master) mode, whereby an internal serial data clock and framing pulse are device outputs. Additionally, two AD7722s can be configured with the serial data outputs connected together.Each converter alternately transmits its conversion data on a shared serial data line.

The part AD7722 provides an accurate on-chip 2.5 V reference. A reference input/output function is provided to allow either the internal reference or an external system reference to be used as the reference source for the part. The AD7722 is available in a 44-pin PQFP package and is specified over the industrial temperature range from 40°C to+85°C.