EVAL-AD7985FMCZ View Datasheet(PDF) - Analog Devices

Part Name

Description

MFG CO.

EVAL-AD7985FMCZ

16-Bit, 2.5 MSPS, PulSAR 15.5 mW ADC in LFCSP

Analog Devices 

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AD7985

Data Sheet

Transfer Functions

The ideal transfer function for the AD7985 is shown in Figure 22

and Table 7.

111 ... 111

111 ... 110

111 ... 101

000 ... 010

000 ... 001

000 ... 000

–FSR

–FSR + 1 LSB

+FSR – 1 LSB

–FSR + 0.5 LSB

+FSR – 1.5 LSB

ANALOG INPUT

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

0V

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.

1.8V

TO

5V 2.5V 2.7V

0V TO VREF

V+

BVDD AVDD, VIO

10Ω

DVDD

TURBO

V–

1.5nF

IN+

IN–

AD7985

SDI

SCK

SDO

REF GND

CNV

VIO

3- OR 4-WIRE

INTERFACE:

SPI, CS,

DAISY CHAIN

(TURBO = LOW)

10µF

NOTES

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

Figure 23. Typical Application Diagram with Multiple Supplies

Rev. C | Page 14 of 28

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