AD7944BCPZ datasheet(15/29 Pages) AD

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AD7944

Data Sheet

Rev. C | Page 14 of 28

Transfer Functions

The ideal transfer characteristic for the AD7944 is shown in

Figure 22 and Table 7.

Figure 22. ADC Ideal Transfer Function

Table 7. Output Codes and Ideal Input Voltages

Description

Analog Input,

VREF = 4.096 V

Digital Output

Code (Hex)

FSR − 1 LSB

4.09575 V

0x3FFF1

Midscale + 1 LSB

2.04825 V

0x2001

Midscale

2.048 V

0x2000

Midscale − 1 LSB

2.04775 V

0x1FFF

−FSR + 1 LSB

250 µV

0x0001

−FSR

0 V

0x00002

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

VREF − REFGND).

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

REFGND).

TYPICAL APPLICATION DIAGRAM

Figure 23 shows an example of the recommended application

diagram for the AD7944 when multiple supplies are available.

Figure 23. Typical Application Diagram with Multiple Supplies

000 ... 000

000 ... 001

000 ... 010

ANALOG INPUT

+FSR – 1.5 LSB

+FSR – 1 LSB

–FSR + 1 LSB

–FSR

–FSR + 0.5 LSB

111 ... 101

111 ... 110

111 ... 111

NOTES

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

AD7944

GND

REF

AVDD,

DVDD

VIO

BVDD

2.5V

1.8V

2.7V

VIO

SDI

SCK

SDO

CNV

3- OR 4-WIRE

INTERFACE:

SPI, CS,

DAISY CHAIN

(TURBO = LOW)

TURBO

10µF

IN+

IN–

1.5nF

10Ω

V–

0V TO VREF

V+

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