ACPL-C740 Optically Isolated Sigma-Delta Modulator

The Broadcom ACPL-C740 is a 1-bit, second-order sigma-delta (Σ-Δ) modulator that converts an analog input signal into a high-speed data stream with galvanic isolation based on optical coupling technology. The ACPL-C740 operates from a 5 V power supply with a dynamic range of 86 dB and an appropriate digital filter. The differential inputs of ±200 mV (full-scale ±320 mV) 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 onboard clock. The signal information is contained in the modulator data, as a density of ones with a data rate of 20 MHz, and the data are encoded and transmitted across the isolation boundary where they are recovered and decoded into a 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 3 V to 5.5 V.

Combined with superior optical-coupling technology, the modulator delivers high noise margins and excellent immunity against isolation-mode transients. With 0.5 mm minimum distance through insulation (DTI), the ACPL-C740 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 the micrometer range. Offered in a stretched SO-8 (SSO-8) package, the isolated ADC delivers the reliability, small size, superior isolation, and over-temperature performance that motor drive designers need to accurately measure current at a much lower price compared to traditional current transducers.