ISO7240CFDWR datasheet(23/46 Pages) TI1

23 / 46 page

OSC

PWM

VREF

LPF

VREF

DCL

OUT

1 S

Isolation Barrier

Low J Frequency

Channel

(DC...100 kbps)

High J Frequency

Channel

(100 kbps...150 Mbps)

ISO7240CF, ISO7240C, ISO7240M

ISO7241C, ISO7241M, ISO7242C, ISO7242M

www.ti.com

SLLS868R – SEPTEMBER 2007 – REVISED SEPTEMBER 2015

9 Detailed Description

9.1 Overview

The isolator in Figure 15 is based on a capacitive isolation barrier technique. The I/O channel of the device

consists of two internal data channels, a high-frequency channel (HF) with a bandwidth from 100 kbps up to 150

Mbps, and a low-frequency channel (LF) covering the range from 100 kbps down to DC. In principle, a single-

ended input signal entering the HF-channel is split into a differential signal via the inverter gate at the input. The

following capacitor-resistor networks differentiate the signal into transients, which then are converted into

differential pulses by two comparators. The comparator outputs drive a NOR-gate flip-flop whose output feeds an

output multiplexer. A decision logic (DCL) at the driving output of the flip-flop measures the durations between

signal transients. If the duration between two consecutive transients exceeds a certain time limit, (as in the case

of a low-frequency signal), the DCL forces the output-multiplexer to switch from the high- to the low-frequency

channel.

Because low-frequency input signals require the internal capacitors to assume prohibitively large values, these

signals are pulse-width modulated (PWM) with the carrier frequency of an internal oscillator, thus creating a

sufficiently high frequency signal, capable of passing the capacitive barrier. As the input is modulated, a low-pass

filter (LPF) is needed to remove the high-frequency carrier from the actual data before passing it on to the output

multiplexer.

9.2 Functional Block Diagram

Figure 15. Conceptual Block Diagram of a Digital Capacitive Isolator

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Product Folder Links: ISO7240CF ISO7240C ISO7240M ISO7241C ISO7241M ISO7242C ISO7242M

ISO7240CFDWR датащи(PDF) 23 Page - Texas Instruments