AD7680 datasheet(13/28 Pages) AD

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AD7688

Rev. A | Page 13 of 28

Transfer Functions

The ideal transfer characteristic for the AD7688 is shown in

Figure 25 and Table 8.

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 8. Output Codes and Ideal Input Voltages

Description

Analog Input

VREF = 5 V

Digital Output Code Hexa

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

TYPICAL CONNECTION DIAGRAM

Figure 26 shows an example of the recommended connection

diagram for the AD7688 when multiple supplies are available.

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

VGND).

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

+ VGND).

AD7688

REF

GND

VDD

IN–

IN+

VIO

SDI

SCK

SDO

CNV

3- OR 4-WIRE INTERFACE5

100nF

μF2

≥7V

≤–2V

1.8V TO VDD

REF1

0 TO VREF

2.7nF

≥7V

≤–2V

VREF TO 0

2.7nF

1SEE 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 Application Diagram with Multiple Supplies

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