AD7940 datasheet(13/28 Pages) AD

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AD7686

Rev. B | Page 13 of 28

Transfer Functions

The ideal transfer characteristic for the AD7686 is shown in

Figure 25 and Table 7.

000...000

000...001

000...010

111...101

111...110

111...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 7. Output Codes and Ideal Input Voltages

Description

Analog Input

VREF = 5 V

Digital Output Code

Hexadecimal

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

TYPICAL CONNECTION DIAGRAM

Figure 26 shows an example of the recommended connection

diagram for the AD7686 when multiple supplies are available.

1 This is also the code for an overranged analog input (VIN+ − VIN− above VREF − V

GND

2 This is also the code for an underranged analog input (V

− V

below V

IN+

IN−

GND

AD7686

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

1SEE THE VOLTAGE REFERENCE INPUT 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 SECTION FOR MOST CONVENIENT INTERFACE MODE.

Figure 26. Typical Application Diagram with Multiple Supplies

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