AD7984 datasheet(13/24 Pages) AD

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AD7984

Rev. 0 | Page 13 of 24

Transfer Functions

The ideal transfer characteristic for the AD7984 is shown in

Figure 22 and Table 7.

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 22. 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

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 VGND).

TYPICAL CONNECTION DIAGRAM

Figure 23 shows an example of the recommended connection

diagram for the AD7984 when multiple supplies are available.

2.7nF

15Ω

V–

0 TO VREF

V+

2.7nF

15Ω

V–

VREF TO 0

V+

10µF2

REF1

REF

VDD

VIO

GND

IN+

IN–

SDI

SCK

SDO

CNV

AD7984

100nF

3-WIRE INTERFACE

2.5V

1.8V TO 5V

V+

ADA48412, 3

NOTES

1SEE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.

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

SEE RECOMMENDED LAYOUT IN FIGURE 40 AND FIGURE 41.

3SEE DRIVER AMPLIFIER CHOICE SECTION.

4OPTIONAL FILTER. SEE ANALOG INPUTS SECTION.

Figure 23. Typical Application Diagram with Multiple Supplies

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