AD7679 datasheet(11/20 Pages) AD

11 / 20 page

REV. B

AD7676

–11–

TYPICAL CONNECTION DIAGRAM

Figure 5 shows a typical connection diagram for the AD7676.

Different circuitry shown on this diagram is optional and is

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. Figure 6 shows a simplified analog input section

of the AD7676.

IN+

IN–

AGND

AVDD

R+ = 684

R– = 684

Figure 6. Simplified Analog Input

The diodes shown in Figure 6 provide ESD protection for the

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

never exceeds the absolute ratings on these inputs. This will

cause these diodes to become forward-biased and start conducting

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 a 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.

FREQUENCY – Hz

10k

10M

100k

Figure 7. Analog Input CMRR vs. Frequency

AVDD

AGND

DGND

DVDD

OVDD

OGND

SER/

PAR

CNVST

BUSY

SDOUT

SCLK

RESET

REFGND

CREF

2.5V REF

NOTE 1

REF

100

CLOCK

AD7676

C/ P/DSP

SERIAL PORT

DIGITAL SUPPLY

(3.3V OR 5V)

ANALOG

SUPPLY

(5V)

DVDD

OB/

NOTE 7

BYTESWAP

DVDD

50k

100nF

IN+

ANALOG INPUT+

2.7nF

NOTE 4

NOTE 5

AD8021

–

NOTE 2

NOTE 3

NOTE 6

ADR421

10 F

100nF

10 F

100nF

10 F

IN–

ANALOG INPUT–

2.7nF

NOTE 4

NOTE 5

AD8021

–

1 F

NOTES

1. SEE VOLTAGE REFERENCE INPUT SECTION.

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

3. OPTIONAL CIRCUITRY FOR HARDWARE GAIN CALIBRATION.

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

5. SEE ANALOG INPUTS 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)

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