AD7652 datasheet(13/23 Pages) AD

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REV. PrA

PRELIMINARY TECHNICAL DATA

AD7667

–13–

Table I. Output Codes and Ideal Input Voltages

Digital Output Code

Hexa

Analog

Straight

Two’s

Description

Input

Binary

Comple-

ment

FSR –1 LSB

2.499962 V

FFFF

7FFF

FSR – 2 LSB

2.499923 V

FFFE

7FFE

Midscale + 1 LSB

1.250038 V

8001

0001

Midscale

1.25 V

8000

0000

Midscale – 1 LSB

1.249962 V

7FFF

FFFF

–FSR + 1 LSB

38 µV

0001

8001

–FSR

0 V

0000

8000

NOTES

1This is also the code for overrange analog input (V

IN – VINGND above

VREF – VREFGND).

2This is also the code for underrange analog input (V

IN below VINGND).

TYPICAL CONNECTION DIAGRAM

Figure 5 shows a typical connection diagram for the AD7667.

Analog Input

Figure 6 shows an equivalent circuit of the input structure of

the AD7667.

OR INGND

AGND

AVDD

Figure 6. Equivalent Analog Input Circuit

The two diodes D1 and D2 provide ESD protection for

the analog inputs IN and INGND. Care must be taken to

ensure that the analog input signal never exceeds the supply

rails by more than 0.3 V. This will cause these diodes to

become forward-biased and start conducting current.

These diodes can handle a forward-biased current of 100

mA maximum. For instance, these conditions could eventu-

ally occur when the input buffer’s (U1) supplies are

100nF

10 F

100nF

10 F

AVDD

10 F

100nF

AGND

DGND

DVDD

OVDD

OGND

WARP

IMPULSE

SER/ PAR

CNVST

BUSY

SDOUT

SCLK

RESET

INGND

REFGND

REF

100

CLOCK

AD7667

ANALOG INPUT

(0V TO 2.5V)

C/ P/DSP

SERIAL

PORT

DIGITAL SUPPLY

(3.3V OR 5V)

ANALOG

SUPPLY

(5V)

NOTES:

1 THE CONFIGURATION SHOWN IS USING THE INTERNAL REFERENCE AND INTERNAL BUFFER

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

3 OPTIONAL LOW JITTER CNVST.

DVDD

OB/ 2C

2.7nF

U12

PDBUF

PDREF

REFBUFIN1

47 F

100 nF

BYTESWAP

Figure 5. Typical Connection Diagram

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