AD7643

Rev. 0 | Page 10 of 28

Pin

No.

Mnemonic

Type1

Description

31

RD

DI

Read Data. When CS and RD are both low, the interface parallel or serial output bus is enabled.

32

CS

DI

Chip Select. When CS and RD are both low, the interface parallel or serial output bus is enabled.

CS is also used to gate the external clock in slave serial mode.

33

RESET

DI

Reset Input. When high, resets the AD7643. Current conversion, if any, is aborted. Falling edge of

RESET enables the calibration mode indicated by pulsing BUSY high. Refer to the Digital Interface

section. If not used, this pin can be tied to DGND.

34

PD

DI

Power-Down Input. When high, powers down the ADC. Power consumption is reduced and

conversions are inhibited after the current one is completed.

35

CNVST

DI

Conversion Start. A falling edge on CNVST puts the internal sample-and-hold into the hold state

and initiates a conversion.

37

REF

AI/O

Reference Output/Input.

When PDREF/PDBUF = low, the internal reference and buffer are enabled producing 2.048 V on this pin.

When PDREF/PDBUF = high, the internal reference and buffer are disabled allowing an externally

supplied voltage reference up to AVDD volts. Decoupling is required with or without the internal

reference and buffer. Refer to the Voltage Reference Input section.

38

REFGND

AI

Reference Input Analog Ground.

39

IN−

AI

Differential Negative Analog Input.

40

NC

No Connect.

43

IN+

AI

Differential Positive Analog Input.

45

TEMP

AO

Temperature Sensor Analog Output. Normally, 278 mV @ 25°C with a temperature coefficient

of 1 mV/°C. This pin can be used to measure the temperature of the AD7643. See the

Temperature Sensor section.

46

REFBUFIN

AI/O

Internal Reference Output/Reference Buffer Input.

When PDREF/PDBUF = low, the internal reference and buffer are enabled producing the 1.2 V (typical)

band gap output on this pin, which needs external decoupling. The internal fixed gain reference

buffer uses this to produce 2.048 V on the REF pin.

When using an external reference with the internal reference buffer (PDBUF = low, PDREF = high),

applying 1.2 V on this pin produces 2.048 V on the REF pin. Refer to the Voltage Reference Input section.

47

PDREF

DI

Internal Reference Power-Down Input.

When low, the internal reference is enabled.

When high, the internal reference is powered down and an external reference must been used.

48

PDBUF

DI

Internal Reference Buffer Power-Down Input.

When low, the buffer is enabled (must be low when using internal reference).

When high, the buffer is powered down.

Table 7. Data Bus Interface Definition

MODE

MODE1

MODE0

D0/OB/2C

D1/A0

D2/A1

D[3]

D[4:9]

D[10:11]

D[12:15]

D[16:17]

Description

0

0

0

R[0]

R[1]

R[2]

R[3]

R[4:9]

R[10:11]

R[12:15]

R[16:17]

18-Bit Parallel

1

0

1

OB/2C

A0 = 0

R[2]

R[3]

R[4:9]

R[10:11]

R[12:15]

R[16:17]

16-Bit High Word

1

0

1

OB/2C

A0 = 1

R[0]

R[1]

All Zeros

16-Bit Low Word

2

1

0

OB/2C

A0 = 0

A1 = 0

All Hi-Z

R[10:11]

R[12:15]

R[16:17]

8-Bit High Byte

2

1

0

OB/2C

A0 = 0

A1 = 1

All Hi-Z

R[2:3]

R[4:7]

R[8:9]

8-Bit Mid Byte

2

1

0

OB/2C

A0 = 1

A1 = 0

All Hi-Z

R[0:1]

All Zeros

8-Bit Low Byte

2

1

0

OB/2C

A0 = 1

A1 = 1

All Hi-Z

All Zeros

R[0:1]

8-Bit Low Byte

3

1

1

OB/2C

All Hi-Z

Serial Interface

Serial Interface