AD7902 datasheet(26/29 Pages) AD

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Data Sheet

AD7902

Rev. B | Page 25 of 28

FUNCTIONAL SAFTEY CONSIDERATIONS

The AD7902 contains two physically isolated ADCs, making it

ideally suited for functional safety applications. Because of this

isolation, each ADC features an independent user interface, an

independent reference input, an independent analog input, and

independent supplies. Physical isolation renders the device

suitable for taking verification/backup measurements while

separating the verification ADC from the system under control.

Although the Simultaneous Sampling section describes how to

operate the device in a simultaneous nature, the circuit is actually

composed of two individual signal chains. This separation makes

the AD7902 ideal for handling redundant measurement

applications. Implementing a signal chain with redundant ADC

measurement can contribute to a no single error system. Figure 52

shows a typical functional safety application circuit consisting of

a redundant measurement with the employment of monitoring the

inverted signal. The inversion is applied to detect common cause

failures where it is expected that the circuit output moves in the

same direction during a fault condition, instead of moving in the

opposite direction as expected.

In addition, the QSOP package that houses the device provides

access to the leads for inspection.

Figure 52. Typical Functional Safety Block Diagram

GND

VDD1 VDD2

2.5V

REF1 REF2

REF = 2.5V TO 5V

ADC1

IN1+

IN1–

VIO1

SDI1

SCK1

CNV1

SDO1

SDI1

SCK1

CNV1

SDO1

SDI2

VIO1

VIO2

SCK2

CNV2

SDO2

ADC2

IN2+

IN2–

VIO2

SDI2

SCK2

CNV2

SDO2

AD7902

PHYSICALLY

ISOLATED ADCs

0V TO VREF

ADA4841-1

VREF

ADA4841-1

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