Isolated Sigma-Delta Modulator

The AD7400 is a second-order, sigma-delta (Σ-Δ) modulator that converts an analog input signal to a high speed, 1-bit data stream with on-chip digital isolation based on Analog Devices, Inc. iCoupler® technology. The AD7400 operates from a 5 V power supply and accepts a differential input signal of ±200 mV (±320 mV full scale). The analog input is continuously sampled by the analog modulator, eliminating the need for external sample-and-hold circuitry. The input information is contained in the output stream as a density of ones with a data rate of 10 MHz. The original information can be reconstructed with an appropriate digital filter. The serial I/O can use a 5 V or a 3 V supply (VDD2).

The serial interface is digitally isolated. High speed CMOS, combined with monolithic air core transformer technology, means the on-chip isolation provides outstanding performance characteristics superior to alternatives such as optocoupler devices. The part contains an on-chip reference. The AD7400 is offered in a 16-lead SOIC and has an operating temperature range of −40°C to +105°C.

An external clock version, AD7401, is also available.

Applications

* AC motor controls

* Data acquisition systems

* A/D + opto-isolator replacements

* 10 MHz clock rate* Second-order modulator* 16 bits no missing codes* ±2 LSB INL typical at 16 bits* 3.5 µV/°C maximum offset drift* On-board digital isolator* On-board reference* Low power operation: 18 mA maximum at 5.25 V* −40°C to +105°C operating range* 16-lead SOIC package