REV. 0

AD7664

–11–

Table I. Output Codes and Ideal Input Voltages

Digital Output Code

Hexa

Analog

Straight

Two’s

Input

Binary

Complement

FSR –1 LSB

2.499962 V

FFFF

1

7FFF

1

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

2

8000

2

NOTES

TYPICAL CONNECTION DIAGRAM

Figure 5 shows a typical connection diagram for the AD7664.

Analog Input

Figure 6 shows an equivalent circuit of the input structure of

the AD7664.

C2

R1

D1

D2

C1

IN

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 eventually occur when the input buffer’s

(U1) supplies are different from AVDD. In such case, an input

buffer with a short circuit current limitation can be used to

protect the part.

100nF

10 F

100nF

10 F

AVDD

10 F

100nF

AGND

DGND

DVDD

OVDD

OGND

WARP

IMPULSE

SER/

PAR

CNVST

BUSY

SDOUT

SCLK

RD

CS

RESET

PD

IN

INGND

REFGND

100nF

REF

100

CLOCK

AD7664

ANALOG INPUT

(0V TO 2.5V)

C/ P/DSP

SERIAL

PORT

DIGITAL SUPPLY

(3.3V OR 5V)

ANALOG

SUPPLY

(5V)

NOTES:

DVDD

OB/

2C

2.7nF

15

Figure 5. Typical Connection Diagram