AD7694 datasheet(15/24 Pages) AD

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Data Sheet

AD7988-1/AD7988-5

Rev. B | Page 15 of 24

Transfer Functions

The ideal transfer characteristic for the AD7988-x is shown in

Figure 30 and Table 7.

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

Figure 30. ADC Ideal Transfer Function

Table 7. 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 CONNECTION DIAGRAM

Figure 31 shows an example of the recommended connection

diagram for the AD7988-x when multiple supplies are available.

AD7988-1/

AD7988-5

2.5V

V+

20Ω

V+

V–

0V TO VREF

1.8V TO 5.5V

100nF

10µF2

2.7nF

100nF

REF

IN+

IN–

VDD

VIO

GND

3- OR 4-WIRE INTERFACE5

REF1

1 SEE THE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.

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

3 SEE THE DRIVER AMPLIFIER CHOICE SECTION.

4 OPTIONAL FILTER. SEE THE ANALOG INPUTS SECTION.

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

CNV

SCK

SDO

SDI

Figure 31. Typical Application Diagram with Multiple Supplies

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