AD8021 datasheet(14/28 Pages) AD

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AD7986

Rev. B | Page 14 of 28

Transfer Functions

The ideal transfer characteristic for the AD7986 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

REF = 5 V

Digital Output

Code (Hex)

FSR − 1 LSB

+4.095969 V

0x1FFFF1

Midscale + 1 LSB

+31.25 µV

0x00001

Midscale

0 V

0x00000

Midscale − 1 LSB

−31.25 µV

0x3FFFF

−FSR + 1 LSB

−4.095969 V

0x20001

−FSR

−4.096 V

0x200002

1 This is also the code for an overranged analog input (V

IN+ − VIN− above VREF −

REFGND).

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

IN+ − VIN− below REFGND).

TYPICAL CONNECTION DIAGRAM

Figure 23 shows an example of the recommended connection

diagram for the AD7986 when multiple supplies are available.

2.7nF

Ω

V–

0V TO VREF

V+

2.7nF

Ω

V–

V+

IN–

AD7986

IN+

REF

AVDD,

DVDD

VIO

BVDD

2.5V

1.8V TO 2.7V

VIO

SDI

SCLK

SDO

CNV

TURBO

10µF

VREF TO 0V

GND1

NOTES

1. GND REFERS TO REFGND, AGND, AND DGND.

3- OR 4-WIRE

INTERFACE:

SPI, CS

DAISY CHAIN (TURBO = LOW)

Figure 23. Typical Application Diagram with Multiple Supplies

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