2

®

ADS7819

7

BASIC OPERATION

Figure 1 shows a basic circuit to operate the ADS7819.

Taking R/C (pin 23) LOW for 40ns will initiate a conver-

sion. BUSY (pin 25) will go LOW and stay LOW until the

conversion is completed and the output registers are up-

dated. Data will be output in Binary Two’s Complement

with the MSB on D11 (pin 6). BUSY going HIGH can be

used to latch the data. All convert commands will be ignored

while BUSY is LOW.

FIGURE 1. Basic Operation

CS

R/C

BUSY

OPERATION

1

X

X

None. Databus in Hi-Z state.

↓

0

1

Initiates conversion. Databus remains in

Hi-Z state.

0

↓

1

Initiates conversion. Databus enters Hi-Z

state.

01

↑

Conversion completed. Valid data from the

most recent conversion on the databus.

↓

1

1

Enables databus with valid data from the

most recent conversion.

↓

1

0

Conversion in progress. Databus in Hi-Z

state, enabled when the conversion is completed.

0

↑

0

Conversion in progress. Databus in Hi-Z

state, enabled when the conversion is completed.

00

↑

Conversion completed. Valid data from the

most recent conversion in the output register

but the output pins D11-D0 are tri-stated.

X

X

0

New convert commands ignored. Conversion

in progress.

Table I. Control Line Functions for ‘read’ and ‘convert’.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

28

27

26

25

24

23

22

21

20

19

18

17

16

15

ADS7819

50

Ω

±2.5V

–5V

+5V

0.1µF

NC

10µF

+

10µF

+

0.1µF

Convert Pulse

BUSY

40ns min

D0 (LSB)

D1

D2

D3

D6

D5

D4

D7

D8

D9

D10

D11 (MSB)

0.1µF 10µF

+

The ADS7819 will begin tracking the input signal at the end

of the conversion. Allowing 1.25

µs between convert com-

mands assures accurate acquisition of a new signal.

STARTING A CONVERSION

The combination of CS (pin 24) and R/C (pin 23) LOW for

a minimum of 40ns puts the sample/hold of the ADS7819 in

the hold state and starts a conversion. BUSY (pin 25) will go

LOW and stay LOW until the conversion is completed and

the internal output register has been updated. All new

convert commands during BUSY LOW will be ignored.

The ADS7819 will begin tracking the input signal at the end

of the conversion. Allowing 1.25

µs between convert com-

mands assures accurate acquisition of a new signal. Refer to

Table I for a summary of CS, R/C, and BUSY states and

Figures 2 and 3 for timing parameters.

DESCRIPTION

ANALOG VALUE

DIGITAL OUTPUT

Full Scale Range

±2.5V

Least Significant

1.22mV

Bit (LSB)

BINARY CODE

HEX CODE

+Full Scale

2.499V

0111 1111 1111

7FF

(2.5V – 1LSB)

Midscale

0V

0000 0000 0000

000

One LSB below

–1.22mV

1111 1111 1111

FFF

Midscale

–Full Scale

–2.5V

1000 0000 0000

800

BINARY TWO'S COMPLEMENT

TABLE II. Ideal Input Voltages and Output Codes.