AD7664ASTZ datasheet(13/25 Pages) AD

13 / 25 page

REV.

–12–

AD7664

The Normal Mode is the fastest mode (500 kSPS) without any

limitation on the time between conversions. This mode makes the

AD7664 ideal for asynchronous applications such as data

acquisition systems, where both high accuracy and fast sample

rate are required.

The Impulse Mode, the lowest power dissipation mode, allows

power saving between conversions. When operating at 100 SPS,

for example, it typically consumes only 21

µW. This feature

makes the AD7664 ideal for battery-powered applications.

Transfer Functions

Using the OB/

2C digital input, the AD7664 offers two output

codings: straight binary and twos complement. The LSB size is

VREF/65536, which is about 38.15

µV. The ideal transfer charac-

teristics for the AD7664 are shown in Figure 4 and Table II.

000...000

000...001

000...010

111...101

111...110

111...111

ANALOG INPUT

VREF – 1.5 LSB

VREF – 1 LSB

1 LSB

0.5 LSB

1 LSB = VREF/65536

Figure 4. ADC Ideal Transfer Function

Table II. Output Codes and Ideal Input Voltages

Digital Output Code

Hexa

Analog

Straight

Twos

Description

Input

Binary

Complement

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

µV0001

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 AD7664.

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

1 F

CREF1

2.5V REF1

REF

100

CLOCK

AD7664

ANALOG INPUT

(0V TO 2.5V)

C/ P/DSP

SERIAL

PORT

DIGITAL SUPPLY

(3.3V OR 5V)

ANALOG

SUPPLY

(5V)

DVDD

OB/

4.7nF

U12

NOTES

1THE ADR421 IS RECOMMENDED WITH C

REF = 47 F.

2THE AD8021 IS RECOMMENDED WITH A COMPENSATION CAPACITOR C

C = 10 pF, TYPE CERAMIC NPO.

3OPTIONAL LOW JITTER CNVST.

Figure 5. Typical Connection Diagram

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