AD7650 datasheet(12/21 Pages) AD

12 / 21 page

REV. 0

–11–

AD7650

Transfer Functions

Using the OB/

2C digital input, the AD7650 offers two output

codings: straight binary and two’s complement. The LSB size is

VREF /65536, which is about 38.15

µV. The ideal transfer char-

acteristic for the AD7650 is shown in Figure 4 and Table I.

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 = V REF/65536

Figure 4. ADC Ideal Transfer Function

Table I. Output Codes and Ideal Input Voltages

Digital Output Code (Hex)

Analog

Straight

Two’s

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

µV

0001

8001

–FSR

0 V

0000

8000

NOTES

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

IN+ – VIN– above VREF – VREFGND).

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

IN+ below VIN–).

NOTES

1. THE ADR421 IS RECOMMENDED WITH CREF = 47 F.

2. THE AD8021 IS RECOMMENDED WITH A COMPENSATION CAPACITOR CC = 10pF, TYPE CERAMIC NPO.

3. OPTIONAL LOW JITTER

CNVST.

AD7650

2.5V REF

NOTE 1

NOTE 2

NOTE 3

CLOCK

C/ P/DSP

SERIAL

PORT

DIGITAL SUPPLY

(3.3V OR 5V)

DVDD

100nF

10 F

100nF

10 F

100

100nF

10 F

ANALOG

SUPPLY

(5V)

CREF1

1 F

4.7nF

ANALOG INPUT

(0V TO 2.5V)

RESET

IMPULSE

WARP

SER/

PAR

OB/

CNVST

BUSY

SDOUT

SCLK

IN–

IN+

REFGND

REF

AGND

AVDD

DGND

DVDD

OVDD

OGND

Figure 5. Typical Connection Diagram

TYPICAL CONNECTION DIAGRAM

Figure 5 shows a typical connection diagram for the AD7650.

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