AD7622

Rev. 0 | Page 16 of 28

TRANSFER FUNCTIONS

Using the OB/2C digital input, the AD7622 offers two output

codings: straight binary and twos complement. The LSB size

Figure 23 and Table 7 for the ideal transfer characteristic.

000...000

000...001

000...010

111...101

111...110

111...111

ANALOG INPUT

+FSR – 1.5 LSB

+FSR – 1 LSB

–FSR + 1 LSB

–FSR

–FSR + 0.5 LSB

Figure 23. ADC Ideal Transfer Function

Table 7. Output Codes and Ideal Input Voltages

Digital Output Code (Hex)

Description

Analog Input

Straight

Binary

Twos

Complement

FSR −1 LSB

+2.047938 V

0xFFFF1

0x7FFF1

FSR − 2 LSB

+2.047875 V

0xFFFE

0x7FFE

Midscale + 1 LSB

+62.5 μV

0x8001

0x0001

Midscale

0 V

0x8000

0x0000

Midscale − 1 LSB

−62.5 μV

0x7FFF

0xFFFF

−FSR + 1 LSB

−2.047938 V

0x0001

0x8001

−FSR

−2.048 V

0x00002

0x80002

RD

CS

100nF

100nF

AVDD

10µF

100nF

AGND

DGND

DVDD

OVDD

OGND

CNVST

BUSY

SDOUT

SCLK

RESET

PD

REFBUFIN

10Ω

D

CLOCK

AD7622

MICROCONVERTER/

MICROPROCESSOR/

DSP

SERIAL

PORT

DIGITAL

INTERFACE

SUPPLY

(2.5V OR 3.3V)

ANALOG

SUPPLY (2.5V)

OVDD

WARP

DIGITAL

SUPPLY (2.5V)

IN+

IN–

U2

15Ω

NOTE 5

50Ω

50pF

NOTE 1

ANALOG

INPUT +

2.7nF

2.7nF

U1

15Ω

NOTE 1

SER/PAR

OB/2C

REFGND

REF

PDBUF

PDREF

100nF

ANALOG

INPUT –

NOTE 2

NOTE 2

NOTE 3

NOTE 4

NOTE 3

NOTE 7

NOTE 6

NORMAL

10µF

10µF

10µF

10kΩ

50pF

1. SEE ANALOG INPUTS SECTION.

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

3. THE CONFIGURATION SHOWN IS USING THE INTERNAL REFERENCE. SEE VOLTAGE REFERENCE INPUT SECTION.

4. A 10µF CERAMIC CAPACITOR (X5R, 1206 SIZE) IS RECOMMENDED (FOR EXAMPLE, PANASONIC ECJ3YB0J106M).

SEE VOLTAGE REFERENCE INPUT SECTION.

5. OPTION, SEE POWER SUPPLY SECTION.

6. OPTION, SEE POWER-UP SECTION.

7. OPTIONAL LOW JITTER CNVST, SEE CONVERSION CONTROL SECTION.

Figure 24. Typical Connection Diagram