Optically Isolated Sigma-Delta Modulator

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The ACPL-7970 miniature isolation amplifier is a 1-bit, second-order amplifier based on sigma-delta modulator technology that converts an analog input signal into a high-speed data stream through integration of galvanic isolation based on optical coupling technology. The ACPL-7970 miniature isolation amplifier uses a 5 V power supply with dynamic range of 78 dB and an appropriate digital filter. The differential inputs of ±200 mV (full scale ±320 mV) are best suited for direct connection to shunt resistors or other low-level signal sources in applications such as motor phase current sensor.

The miniature isolation amplifier analog input is continuously measured by the sigma-delta modulator through 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 10 MHz. Data is then encoded and transmitted across the isolation boundary where it is 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 3 V to 5.5 V.

Combined with superior optical coupling technology, the sigma-delta modulator delivers high noise margins and excellent immunity against isolation-mode transients. With 0.5 mm minimum distance through insulation (DTI), the ACPL-7970 miniature isolation amplifier provides reliable reinforced insulation and high working insulation voltage, which is suitable for fail-safe designs. This 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 designers need to accurately measure current. This design alternative delivers a lower price when compared to traditional current transducers.

The ACPL-7970 miniature isolation amplifier product is also available from Broadcom in an SSO-8 package version, the ACPL-C797 device. And, an external clock version of this miniature isolation amplifier, which comes in an SO-16 package, is also available - the ACPL-796J device.



  • 10 MHz internal clock
  • 1-bit, second-order sigma-delta modulator
  • 16 bits resolution no missing codes (12 bits ENOB)
  • 78 dB SNR
  • 7 µV/°C maximum offset drift
  • ±1% maximum gain error
  • Internal reference voltage
  • ±200 mV linear range with single 5 V supply (±320 mV full scale)
  • 3 V to 5.5 V wide supply range for digital interface
  • –40°C to +105°C operating temperature range
  • 25 kV/µs common-mode transient immunity
  • Safety and regulatory Approval (pending): 
    • UL 1577 (5000 Vrms/1 min.)
    • CSA
    • IEC/EN/DIN EN 60747-5-5
  • Options available are :
    • 000E: Lead Free Option
    • 300E: Gullwing Surface Mount Option
    • 500E: Tape and Reel Packaging Option


  • Motor Phase and Rail Current Sensor
  • Power Inverter Current Sensing and Voltage Sensing
  • Industrial Process Control
  • Data Acquisition Systems
  • General Purpose Current sensing and Voltage Sensing
  • Traditional Hall Effect Current Sensor Replacements

Lifecycle Status


Substance Compliance

  • RoHS6
    Fully Compliant
Specification Value
Lifecycle Active
Distrib. Inventory Yes
RoHS6 Compliant Y
Product Type Isolated Modulator
Package DIP 8
Gain Error at 25 Deg C (%) Max ±1
VDD2 (V) 3 - 5.5
CMR (min.) (V/µs) 25000.0
Vcm (V) 1000.0
UL Insulation Rating Viso (VRMS) 5000.0
IEC Maximum Working Insulation Voltage Viorm (VPEAK) 891.0
IEC Highest Allowable Overvoltage Viotm (VPEAK) 8000
Application Note2 i
Brochures1 i
Product Change Notice (PCN)3 i
Regulatory Certificate1 i
Reliability Data Sheet2 i
Technical Notes1 i
White Papers2 i
FAQs1 i
Promotional Material1 i


Optically Isolated Sigma-Delta Modulator


Optically Isolated Sigma-Delta Modulator ACPL-796J, External Clock


Precision Miniature Isolation Amplifiers