AD7985BCPZ datasheet(14/28 Pages) AD

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AD7985

Rev. 0 | Page 14 of 28

Transfer Functions

The ideal transfer characteristic for the AD7985 is shown in

Figure 22 and Table 7.

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

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

4.095938 V

0xFFFF1

Midscale + 1 LSB

2.048063 V

0x8001

Midscale

2.048 V

0x8000

Midscale – 1 LSB

2.047938 V

0x7FFF

–FSR + 1 LSB

62.5 μV

0x0001

–FSR

0 V

0x00002

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

REFGND).

2 This is also the code for an underranged analog input (VIN+ − VIN− below REFGND).

TYPICAL CONNECTION DIAGRAM

Figure 23 shows an example of the recommended connection

diagram for the AD7985 when multiple supplies are available.

NOTES

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

AD7985

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–

2.7nF

15Ω

V–

0V TO VREF

V+

Figure 23. Typical Application Diagram with Multiple Supplies

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