Isolated Sigma-Delta Modulator

The AD7401 is a second-order, sigma-delta (Σ-Δ) modulator that converts an analog input signal into a high speed, 1-bit data stream with on-chip digital isolation based on Analog Devices, Inc., iCoupler® technology. The AD7401 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 up to 20 MHz. The original information can be reconstructed with an appropriate digital filter. The serial input/output 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 device contains an on-chip reference. The AD7401 is offered in a 16-lead SOIC and has an operating temperature range of −40°C to +105°C.

An internal clock version, AD7400, is also available.

APPLICATIONS

* AC motor controls

* Data acquisition systems

* A/D + opto-isolator replacements

* 20 MHz maximum external 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