AD7682 datasheet(12/20 Pages) AD

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AD7689

Preliminary Technical Data

Rev. PrC | Page 12 of 20

TRANSFER FUNCTIONS

With the inputs configured for unipolar range (single ended,

COM with ground sense, or paired differentially with IN- as

ground sense), the data output is straight binary.

With the inputs configured for bipolar range (COM = VREF/2, or

paired differentially with IN- = VREF/2), the data outputs are

two’s complement.

The ideal transfer characteristic for the AD7689 is shown in

Figure 12 and Table 8 for both unipolar and bipolar ranges with

the internal 4.096V reference.

100...000

100...001

100...010

011...101

011...110

011...111

2’s COMP STRAIGHT

BINARY

000...000

000...001

000...010

111...101

111...110

111...111

ANALOG INPUT

+FSR – 1.5LSB

+FSR – 1LSB

–FSR + 1LSB

–FSR

–FSR + 0.5LSB

Figure 12. ADC Ideal Transfer Function

Table 8. Output Codes and Ideal Input Voltages

Description

Unipolar Analog Input1

VREF = 4.096 V

Digital Output

Code (Straight

Binary Hex)

Bipolar Analog Input2

VREF = 4.096 V

Digital Output

Code (2’s Complement

Hex)

FSR − 1 LSB

4.095938 V

0xFFFF3

+2.047938 V

0x7FFF

Midscale + 1 LSB

2.048063 V

0x8001

62.5

μV

0x0001

Midscale

2.048 V

0x8000

0x00004

Midscale − 1 LSB

2.047938 V

0x7FFF

-62.5

μV

0xFFFF3

−FSR + 1 LSB

62.5

μV

0x0001

-2.047938 V

0x8001

−FSR

0 V

0x00004

-2.048 V

0x8000

1 With COM or IN- = 0 V or all INx referenced to GND.

2 With COM or IN- = VREF /2.

3 This is also the code for an overranged analog input ((IN+) − (IN-) , or COM, above VREF − VGND).

4 This is also the code for an underranged analog input ((IN+) − (IN-), or COM, below VGND).

TYPICAL CONNECTION DIAGRAM

Figure 13 shows an example of the recommended connection

diagram for the AD7689 when multiple supplies are available.

AD7689

REF

GND

VDD

VIO

DIN

SCK

SDO

CNV

3-WIRE INTERFACE 4

100nF

22µF2

V+

V–

1.8V TO VDD

0TO VREF

V+

V–

ADA4841-x3

1INTERNAL REFERNCE SHOWN. SEE REFERENCE SECTION FOR REFERENCE SELECTION.

2CREF IS USUALLY A 22µF CERAMIC CAPACITOR (X5R).

3SEE DRIVER AMPLIFIER SECTION FOR ADDITIONAL RECOMMENDED AMPLIFIERS.

4SEE THE DIGITAL INTERFACE SECTION FOR CONFIGURING AND READING CONVERSION DATA.

IN0

INn

COM

REFIN

100nF

0TO VREF

0 V or

REF

Figure 13. Typical Application Diagram with Multiple Supplies

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