AD7980BCPZ-R2 datasheet(17/28 Pages) AD

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Data Sheet

AD7980

Rev. F | Page 15 of 26

Transfer Functions

The ideal transfer characteristic for the AD7980 is shown in

Figure 26 and Table 8.

Figure 26. ADC Ideal Transfer Function

Table 8. Output Codes and Ideal Input Voltages

Analog Input

Description

VREF = 5 V

Digital Output Code (Hex)

FSR − 1 LSB

4.999924 V

FFFF1

Midscale + 1 LSB

2.500076 V

8001

Midscale

2.5 V

8000

Midscale − 1 LSB

2.499924 V

7FFF

−FSR + 1 LSB

76.3 µV

0001

−FSR

0 V

00002

This is also the code for an overranged analog input (VIN+ − VIN− above VREF − VGND).

This is also the code for an underranged analog input (VIN+ − VIN− below VGND).

TYPICAL APPLICATION CIRCUIT WITH MULTIPLE

SUPPLIES

Figure 27 shows an example of a typical application circuit for

the AD7980 when multiple supplies are available.

Figure 27. Typical Application Circuit with Multiple Supplies

000 ... 000

000 ... 001

000 ... 010

111 ... 101

111 ... 110

111 ... 111

–FSR –FSR + 1LSB

–FSR + 0.5LSB

+FSR – 1 LSB

+FSR – 1.5 LSB

ANALOG INPUT

AD7980

3- OR 4-WIRE INTERFACE

2.5V

V+

20Ω

V+

V–

0 TO VREF

1.8V TO 5V

100nF

10µF2

2.7nF

100nF

REF

IN+

IN–

VDD

VIO SDI

CNV

SCK

SDO

GND

REF1

1SEE THE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.

2CREF IS USUALLY A 10µF CERAMIC CAPACITOR (X5R).

3SEE THE DRIVER AMPLIFIER CHOICE SECTION.

4OPTIONAL FILTER. SEE THE ANALOG INPUT SECTION.

5SEE THE DIGITAL INTERFACE FOR THE MOST CONVENIENT INTERFACE MODE.

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