AD7687BCPZ-R2 datasheet(16/27 Pages) AD

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Data Sheet

AD7687

Rev. E | Page 15 of 26

Transfer Functions

Figure 25 and Table 9 show the ideal transfer characteristic for

the AD7687.

100...000

100...001

100...010

011...101

011...110

011...111

ANALOG INPUT

+FSR – 1.5 LSB

FSR – 1 LSB

–FSR + 1 LSB

–FSR

–FSR + 0.5 LSB

Figure 25. ADC Ideal Transfer Function

Table 9. Output Codes and Ideal Input Voltages

Description

Analog Input

VREF = 5 V

Digital Output Code

Hexadecimal

FSR − 1 LSB

+4.999847 V

7FFF1

Midscale + 1 LSB

+152.6 µV

0001

Midscale

0 V

0000

Midscale − 1 LSB

−152.6 µV

FFFF

−FSR + 1 LSB

−4.999847 V

8001

−FSR

−5 V

80002

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

−VREF + VGND).

TYPICAL CONNECTION DIAGRAM

Figure 26 shows an example of the recommended connection

diagram for the AD7687 when multiple supplies are available.

AD7687

REF

GND

VDD

IN–

IN+

VIO

SDI

SCK

SDO

CNV

3- OR 4-WIRE INTERFACE5

100nF

10µF2

≥7V

≤–2V

1.8V TO VDD

REF1

0 TO VREF

33Ω

2.7nF

≥7V

≤–2V

VREF TO 0

33Ω

2.7nF

1SEE VOLTAGE INPUT REFERENCE SECTION FOR REFERENCE SELECTION.

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

3SEE DRIVER AMPLIFIER CHOICE SECTION.

4OPTIONAL FILTER. SEE ANALOG INPUT SECTION.

5SEE DIGITAL INTERFACE FOR MOST CONVENIENT INTERFACE MODE.

Figure 26. Typical Connection Diagram with Multiple Supplies

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