ACPL-C877 datasheet(13/18 Pages) ABRACON

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ACPL-C877 Data Sheet

Precision Optically Isolated Digital Voltage Sensor

Broadcom

ACPL-C877-DS100

Product Overview

Description

The ACPL-C877 isolated digital voltage sensor converts an

analog input signal into a high-speed (10 MHz typical)

single-bit data stream by means of a sigma-delta over-

sampling modulator. The time average of the modulator

data is directly proportional to the input signal voltage. The

modulator uses internal clock of 10 MHz. The modulator

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 is represented by the density of ones in

the data output.

The other main function of the modulator (optocoupler) is to

provide galvanic isolation between the analog signal input

and the digital data output. It provides high noise margins

and excellent immunity against isolation-mode transients

that allows direct measurement of low-level signals in highly

noisy environments, for example measurement of motor

bus voltage in power inverters.

With 0.5-mm minimum DTI, the ACPL-C877 provides

reliable double protection 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 an SSO-

8 package, the isolated ADC delivers the reliability, small

size, superior isolation and over-temperature performance

motor drive designers need to accurately measure voltage.

Analog Input

The ACPL-C877 front-end contains a fully-differential

amplifier followed by a sigma-delta modulator. The fully-

differential analog inputs accept signals of 0V to 2V (full

scale from -0.1V to 3.2V), which is ideal for direct

connection to resistive divider network for voltage sensing

or other high-level signal sources applications such as

motor drive DC-link bus voltage sensing and insulation

resistance voltage measurement usually used together with

Broadcom® ASSR-601J high voltage photo-mosfet relay.

Users are able to use higher input range from 2V to 3.2V, as

long as within full-scale range (3.2V), for the purpose of

over-voltage or overload detection.

Latch-up Consideration

Latch-up risk of CMOS devices needs careful consideration,

especially in applications with direct connection to signal

source that is subject to frequent transient noise. The

analog input structure of the ACPL-C877 is designed to be

resilient to transients and surges, which are often

encountered in highly noisy application environments such

as motor drive and other power inverter systems. Other

situations could cause transient voltages to the inputs

include short circuit and overload conditions. The ACPL-

C877 is tested with DC voltage of up to –2V and 2-second

transient voltage of up to –6V to the analog inputs with no

latch-up or damage to the device.

Modulator Data Output

Input signal information is contained in the modulator output

data stream, represented by the density of ones and zeros.

The density of ones is proportional to the input signal

voltage, as shown in Figure 14. A differential input signal of

0V ideally produces a data stream of ones and zeros in

equal densities. A differential input of 2V corresponds to

81.25% density of ones. A differential input of 3.2V or higher

results in ideally all ones in the data stream, while input less

than -0.1V is not defined. Table 3 shows this relationship.

ACPL-C877 Datasheet(PDF) 13 Page - Abracon Corporation

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