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ACPL-7970

Optically Isolated Sigma-Delta Modulator

Avago Technologies 

ACPL-7970

Optically Isolated Sigma-Delta Modulator

Data Sheet

Description

The ACPL-7970 is a 1-bit, second-order sigma-delta (∑-∆)

modulator converts an analog input signal into a high-

speed data stream with galvanic isolation based on optical

coupling technology. The ACPL-7970 operates from a 5 V

power supply with dynamic range of 78 dB with an appro-

priate 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 on-board clock. The

signal information is contained in the modulator data, as a

density of ones with data rate of 10 MHz, 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 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‑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 reliabil-

ity, small size, superior isolation and over-temperature

performance motor drive designers need to accurately

measure current at much lower price compared to tradi-

tional current transducers.

The external clock version modulator ACPL-796J (SO-16

package) is also available.

Features

• 10 MHz internal clock

• 1-bit, second-order sigma-delta modulator

• 16 bits resolution no missing codes (12 bits ENOB)

• 78 dB SNR

• 6 mV/°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/ms common-mode transient immunity

• Safety and regulatory approvals:

– IEC/EN/DIN EN 60747-5-5: 891 Vpeak working

insulation voltage

– UL 1577: 5000 Vrms/1min isolation voltage

– CSA: Component Acceptance Notice #5

Applications

• Motor phase and rail current sensing

• Power inverter current and voltage sensing

• Industrial process control

• Data acquisition systems

• General purpose current and voltage sensing

• Traditional current transducer replacements

Functional Block Diagram

VDD1

VIN+

VIN–

Σ-∆

MODULATOR/

ENCODER

LED

DRIVER

CLK

DECODER

SHIELD

VDD2

MCLK

MDAT

GND1

VREF

GND2

CAUTION: It is advised that normal static precautions be taken in handling and assembly

of this component to prevent damage and/or degradation which may be induced by ESD.

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