AD7676(Rev0) Просмотр технического описания (PDF) - Analog Devices

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AD7676
(Rev.:Rev0)

16-Bit,
1 LSB INL, 500 kSPS, Differential ADC

Analog Devices 

ANALOG

SUPPLY

(5V)

+ 10␮F 100nF

100⍀

NOTE 5

+ 10␮F

DVDD

100nF

AD7676

100nF + 10␮F

DIGITAL SUPPLY

(3.3V OR 5V)

ADR421

2.5V REF

NOTE 1

1M⍀

100nF

50k⍀ + CREF

NOTE 2

1␮F

NOTE 3

50⍀

AVDD

REF

AGND

REFGND

–

15⍀

NOTE 4 U1

IN+

ANALOG INPUT+

+

AD8021

CC

2.7nF

NOTE 5

50⍀

–

15⍀

NOTE 4 U2

IN–

ANALOG INPUT–

+

AD8021

CC

2.7nF

NOTE 5

DGND DVDD OVDD

OGND

SCLK

SDOUT

BUSY

CNVST

AD7676

OB/2C

SER/PAR

SERIAL PORT

50⍀

D

NOTE 7

DVDD

␮C/␮P/DSP

CS

RD

BYTESWAP

RESET

PD

CLOCK

NOTES

1. SEE VOLTAGE REFERENCE INPUT SECTION.

2. WITH THE RECOMMENDED VOLTAGE REFERENCES, CREF IS 47␮F. SEE CHAPTER VOLTAGE REFERENCE INPUT SECTION

3. OPTIONAL CIRCUITRY FOR HARDWARE GAIN CALIBRATION.

4. THE AD8021 IS RECOMMENDED. SEE DRIVER AMPLIFIER CHOICE SECTION.

5. SEE ANALOG INPUT SECTION.

6. OPTION, SEE POWER SUPPLY SECTION

7. OPTIONAL LOW JITTER CNVST, SEE CONVERSION CONTROL SECTION.

Figure 5. Typical Connection Diagram. (±2.5 V Range Shown)

TYPICAL CONNECTION DIAGRAM

Figure 5 shows a typical connection diagram for the AD7676.

Different circuitry shown on this diagram are optional and are

discussed below.

Analog Inputs

The AD7676 is specified to operate with a differential ± 2.5 V

range. The typical input impedance for each analog input range

is also shown.

AVDD

cause these diodes to become forward-biased and start conduct-

ing current. These diodes can handle a forward-biased current

of 120 mA maximum. This condition could eventually occur

when the input buffer’s (U1) or (U2) supplies are different

from AVDD. In such case, an input buffer with a short-circuit

current limitation can be used to protect the part.

This analog input structure is a true differential structure. By

using these differential inputs, signals common to both inputs

are rejected as shown in Figure 7 which represents the typical

CMRR over frequency.

R+ = 684⍀

IN+

CS

CS

IN–

R– = 684⍀

AGND

Figure 6. AD7676 Simplified Analog Input

Figure 6 shows a simplified analog input section of the AD7676.

The diodes shown in Figure 6 provide ESD protection for the

inputs. Care must be taken to ensure that the analog input sig-

nal never exceeds the absolute ratings on these inputs. This will

REV. 0

–11–

85

80

75

70

65

60

55

50

45

40

1k

10k

100k

1M

10M

FREQUENCY – Hz

Figure 7. Analog Input CMRR vs. Frequency

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