AD7660 datasheet(12/21 Pages) AD

12 / 21 page

REV.

AD7660

–11–

100nF

10 F

100nF

10 F

AVDD

10 F

100nF

AGND

DGND

DVDD

OVDD

OGND

SER/

PAR

CNVST

BUSY

SDOUT

SCLK

RESET

INGND

NOTE 2

REFGND

CREF

NOTE 1

2.5V REF

NOTE 1

REF

100

NOTE 3

CLOCK

AD7660

ANALOG INPUT

(0V TO 2.5V)

C/ P/DSP

SERIAL

PORT

DIGITAL SUPPLY

(3.3V OR 5V)

ANALOG

SUPPLY

(5V)

DVDD

OB/

NOTES

1. WITH THE AD780 OR THE ADR291 VOLTAGE REFERENCE, CREF IS 47 F,

SEE VOLTAGE REFERENCE INPUT SECTION.

2. THE OP184 IS RECOMMENDED.

3. OPTIONAL LOW JITTER

CNVST.

Figure 5. Typical Connection Diagram

Transfer Functions

Using the OB/

2C digital input, the AD7660 offers two output

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

VREF/65536, which is about 38.15

mV. The ideal transfer charac-

teristic for the AD7660 is 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 (Hex)

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

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 AD7660.

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