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Single-Channel Isolated SPI Delta-Sigma A/D Converter Using IL717

This circuit illustrates a typical single-channel delta-sigma isolated ADC

SPI interface. The A/D is located on the bridge with no signal

conditioning electronics between the bridge sensor and the ADC. In this

case, the IL717 is the best choice for isolation. It isolates the control bus

from the microcontroller. The system clock is located on the isolated side

of the system.

Bridge +

Serial Data Out

Serial Data In

Data Clock

Chip Select

Iso SD Out

Iso DS In

Iso Data Clock

Iso CS

Bridge -

IL717

CS5532

Bridge

Bias

Delta Sigma A/D

Multi-Channel Isolated

Sampling A/D Converter

The IL261 is ideal for isolating multi-

channel sampling ADCs. Isolated

channels A0 and A1 control the analog

channel being sampled, while the three

remaining IL261 I/O lines isolate the

SPI interface.

Data Clock

Iso SD Out

Iso Data Clock

IL261

Sampling ADC

Isolation

Boundary

ADS7825

Channel A1

Serial Data Out

R/C

Channel A0

Iso Ch A1

Iso Ch A0

Iso Read/Conv

Analog Ch 0

Analog Ch 1

Analog Ch 2

Analog Ch 3

ADC and DAC Illustrative Applications