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Data Sheet

AD7690

Transfer Functions

The ideal transfer characteristic for the AD7690 is shown in

Figure 25 and Table 7.

Figure 25. ADC Ideal Transfer Function

Table 7. Output Codes and Ideal Input Voltages

Description

Analog Input

VREF = 5 V

Digital Output

Code (Hex)

FSR − 1 LSB

+4.999962 V

0x1FFFF1

Midscale + 1 LSB

+38.15 µV

0x00001

Midscale

0 V

0x00000

Midscale − 1 LSB

−38.15 µV

0x3FFFF

−FSR + 1 LSB

−4.999962 V

0x20001

−FSR

−5 V

0x200002

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 26 shows an example of the recommended connection

diagram for the AD7690 when multiple supplies are available.

Figure 26. Typical Application Diagram with Multiple Supplies

100...000

100...001

100...010

011...101

011...110

011...111

ANALOG INPUT

+FSR – 1.5LSB

+FSR – 1LSB

–FSR + 1LSB

–FSR

–FSR + 0.5LSB

AD7690

REF

GND

VDD

IN–

IN+

VIO

SDI

SCK

SDO

CNV

3- OR 4-WIRE INTERFACE5

100nF

10µF2

V+

V–

1.8V TO VDD

REF1

0 TO VREF

15Ω

2.7nF

V+

V–

VREF TO 0

15Ω

2.7nF

ADA4841-2 3

1 SEE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.

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

3 SEE TABLE 8 FOR ADDITIONAL RECOMMENDED AMPLIFIERS.

4 OPTIONAL FILTER. SEE ANALOG INPUT SECTION.

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

Rev. C | Page 13 of 24

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