AD76881 Просмотр технического описания (PDF) - Analog Devices

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AD76881

18-Bit, 2 MSPS PulSAR 15 mW ADC in LFCSP (QFN)

Analog Devices 

AD7986

Transfer Functions

The ideal transfer characteristic for the AD7986 is shown in

Figure 22 and Table 7.

011 ... 111

011 ... 110

011 ... 101

100 ... 010

100 ... 001

100 ... 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

FSR − 1 LSB

Analog Input

VREF = 5 V

+4.095969 V

Digital Output

Code (Hex)

0x1FFFF1

Midscale + 1 LSB

+31.25 µV

0x00001

Midscale

0V

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 (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 AD7986 when multiple supplies are available.

V+

0V TO VREF

V–

V+

VREF TO 0V

V–

15Ω

2.7nF

15Ω

2.7nF

5V 2.5V 1.8V TO 2.7V

BVDD AVDD, VIO

DVDD

TURBO

IN+

SDI

AD7986 SCLK

SDO

IN–

CNV

REF GND1

10µF

VIO

3- OR 4-WIRE

INTERFACE:

SPI, CS

DAISY CHAIN (TURBO = LOW)

NOTES

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

Figure 23. Typical Application Diagram with Multiple Supplies

Rev. B | Page 14 of 28

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