AD673

REV. A

–3–

ORDERING GUIDE

Temperature

Relative

Model

Range

Accuracy

Package Option

1

AD673JN

0

°C to +70°C

±1/2 LSB max

Plastic DIP (N-20)

AD673JD

0

°C to +70°C

±1/2 LSB max

Ceramic DIP (D-20)

AD673SD

2

–55

°C to +125°C

±1/2 LSB max

Ceramic DIP (D-20)

AD673JP

0

°C to +70°C

±1/2 LSB max

PLCC (P-20A)

NOTES

Analog Devices Military Products Databook .

ABSOLUTE MAXIMUM RATINGS

V+ to Digital Common . . . . . . . . . . . . . . . . . . . . . 0 V to +7 V

V– to Digital Common . . . . . . . . . . . . . . . . . . . 0 V to –16.5 V

Analog Common to Digital Common . . . . . . . . . . . . . . .

±1 V

Analog Input to Analog Common . . . . . . . . . . . . . . . . .

±15 V

Control Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V to V+

Digital Outputs (High Impedance State) . . . . . . . . . . 0 V to V+

Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 mW

FUNCTIONAL DESCRIPTION

A block diagram of the AD673 is shown in Figure 1. The posi-

tive CONVERT pulse must be at least 500 ns wide. DR goes

high within 1.5

µs after the leading edge of the convert pulse in-

dicating that the internal logic has been reset. The negative edge

of the CONVERT pulse initiates the conversion. The internal

8-bit current output DAC is sequenced by the integrated injec-

tion logic (I

most significant bit to least significant bit to provide an output

current which accurately balances the input signal current

through the 5 k

Ω resistor. The comparator determines whether

the addition of each successively weighted bit current causes the

DAC current sum to be greater or less than the input current; if

the sum is more, the bit is turned off. After testing all bits, the

SAR contains a 8-bit binary code which accurately represents

the input signal to within (0.05% of full scale).

BURIED ZENER REF

COMP-

ARATOR

ANALOG

IN

DB7

V+

V–

DIGITAL

COMMON

CONVERT

INT

CLOCK

8-BIT

SAR

DB6

DB5

DB4

DB3

DB2

DB1

DB0

MSB

LSB

ANALOG

COMMON

BIPOLAR

OFFSET

CONTROL

DATA

READY

AD673

5k

DATA

ENABLE

8-BIT

CURRENT

OUTPUT

DAC

Figure 1. AD673 Functional Block Diagram

The SAR drives DR low to indicate that the conversion is com-

plete and that the data is available to the output buffers. DATA

ENABLE

can then be activated to enable the 8-bits of data de-

sired. DATA ENABLE should be brought high prior to the next

conversion to place the output buffers in the high impedance state.

The temperature compensated buried Zener reference provides

the primary voltage reference to the DAC and ensures excellent

stability with both time and temperature. The bipolar offset in-

put controls a switch which allows the positive bipolar offset

current (exactly equal to the value of the MSB less 1/2 LSB) to

be injected into the summing (+) node of the comparator to off-

set the DAC output. Thus the nominal 0 V to +10 V unipolar

input range becomes a –5 V to +5 V range. The 5 k

Ω thin-film

input resistor is trimmed so that with a full-scale input signal, an

input current will be generated which exactly matches the DAC

output with all bits on.

UNIPOLAR CONNECTION

The AD673 contains all the active components required to per-

form a complete A/D conversion. Thus, for many applications,

all that is necessary is connection of the power supplies (+5 V

and –12 V to –15 V), the analog input and the convert pulse.

However, there are some features and special connections which

should be considered for achieving optimum performance. The

functional pinout is shown in Figure 2.

The standard unipolar 0 V to +10 V range is obtained by short-

ing the bipolar offset control pin (Pin 16) to digital common

(Pin 17).

14

13

12

11

17

16

15

20

19

18

10

9

8

1

2

3

4

7

6

5

TOP VIEW

(Not to Scale)

AD673

CONNECTED TO TEST POINTS AND SHOULD BE LEFT FLOATING

NC

*

DIGITAL COMMON

DATA READY

NC

DATA ENABLE

NC

*

LSB DB0

DB1

ANALOG IN

ANALOG COMMON

BIPOLAR OFFSET

DB2

DB3

DB4

DB5

DB6

MSB DB7

V+

CONVERT

V–

PIN 1

IDENTIFIER

Figure 2. AD673 Pin Connections