Isolated Sigma-Delta Modulator

The AD7400A is a second-order, 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 AD7400A operates from a 5 V power supply and accepts a differential input signal of ±250 mV (±320 mV full scale). The analog input is sampled continuously 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 and has an operating temperature range of −40°C to +125°C. The AD7400A is offered in an 8-lead surface-mount PDIP with gull wing leads and a 16-lead SOIC package.

Applications

* AC motor controls

* Shunt current monitoring

* Data acquisition systems

* Analog-to-digital and opto-isolator replacements

* 10 MHz clock rate

* Second-order modulator

* 16 bits no missing codes

* ±2 LSB INL typical at 16 bits

* 1.5 μV/°C typical offset drift