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ADS8405

SLAS427 – DECEMBER 2004

Terminal Functions

NAME

NO.

I/O

DESCRIPTION

AGND

5, 8, 11, 12, 14,

–

Analog ground

15, 44, 45

BDGND

25, 35

–

Digital ground for bus interface digital supply

BUSY

36

O

Status output. High when a conversion is in progress.

BYTE

39

I

Byte select input. Used for 8-bit bus reading. 0: No fold back 1: Low byte D[7:0] of the 16 most

significant bits is folded back to high byte of the 16 most significant pins DB[15:8].

CONVST

40

I

Convert start. The falling edge of this input ends the acquisition period and starts the hold

period.

CS

42

I

Chip select. The falling edge of this input starts the acquisition period.

8-Bit Bus

16-Bit Bus

Data Bus

BYTE = 0

BYTE = 1

BYTE = 0

DB15

16

O

D15 (MSB)

D7

D15 (MSB)

DB14

17

O

D14

D6

D14

DB13

18

O

D13

D5

D13

DB12

19

O

D12

D4

D12

DB11

20

O

D11

D3

D11

DB10

21

O

D10

D2

D10

DB9

22

O

D9

D1

D9

DB8

23

O

D8

D0 (LSB)

D8

DB7

26

O

D7

All ones

D7

DB6

27

O

D6

All ones

D6

DB5

28

O

D5

All ones

D5

DB4

29

O

D4

All ones

D4

DB3

30

O

D3

All ones

D3

DB2

31

O

D2

All ones

D2

DB1

32

O

D1

All ones

D1

DB0

33

O

D0 (LSB)

All ones

D0 (LSB)

–IN

7

I

Inverting input channel

+IN

6

I

Noninverting input channel

NC

3

–

No connection

REFIN

1

I

Reference input

REFM

47, 48

I

Reference ground

REFOUT

2

O

Reference output. Add 1-µF capacitor between the REFOUT pin and REFM pin when the

internal reference is used.

RESET

38

I

Current conversion is aborted and output latches are cleared (set to zeros) when this pin is

asserted low. RESET works independantly of CS.

RD

41

I

Synchronization pulse for the parallel output. When CS is low, this serves as the output enable

and puts the previous conversion result on the bus.

+VA

4, 9, 10, 13, 43,

–

Analog power supplies, 5-V dc

46

+VBD

24, 34, 37

–

Digital power supply for bus

8