Optically Isolated Sigma-Delta Modulators
Avago Technologies Optically Isolated Sigma-Delta Modulators are 1-bit, second-order sigma-delta (Σ-Δ) modulators that convert an analog input signal into a high-speed data stream with galvanic isolation based on optical coupling technology. Avago Technologies Optically Isolated Sigma-Delta Modulators operate from a 5V power supply with a dynamic range of 78dB with an appropriate digital filter. The differential inputs of ±200mV (full scale ±320mV) are ideal for direct connection to shunt resistors or other low-level signal sources in applications such as motor phase current measurement.
The analog input is continuously sampled by a means of sigma-delta over-sampling using an on-board clock. The signal information is contained in the modulator data, as a density of ones with data rate of 10MHz, and the data are encoded and transmitted across the isolation boundary where they are recovered and decoded into high-speed data stream of digital ones and zeros. The original signal information can be reconstructed with a digital filter. The serial interface for data and clock has a wide supply range of 3V to 5.5V.
Combined with superior optical coupling technology, the modulator delivers high noise margins and excellent immunity against isolation-mode transients. With 0.5mm minimum distance through insulation (DTI), the ACPL-7970 provides reliable reinforced insulation and high working insulation voltage, which is suitable for fail-safe designs. This outstanding isolation performance is superior to alternatives including devices based on capacitive- or magnetic-coupling with DTI in micro-meter range. Offered in a DIP-8 package, the isolated ADC delivers the reliability, small size, superior isolation and over-temperature performance motor drive needed to accurately measure current.