AD571

REV. A

–4–

BIT 9

BIT 8

BIT 10 (LSB)

DATA READY

BIT 5

BIT 4

BIT 3

ANALOG IN

V–

BIT 7

BIT 6

DIGITAL COM

BIT 2

BLK AND CONV

(MSB) BIT 1

V+

ANALOG COM

BIPOLAR OFF

1

2

18

17

5

6

7

14

13

12

3

4

16

15

8

11

9

10

TOP VIEW

(Not to Scale)

AD571

Figure 3. AD571 Pin Connections

FULL-SCALE CALIBRATION

The 5 k

Ω thin-film input resistor is laser trimmed to produce a

current which matches the full-scale current of the internal

DAC—plus about 0.3%—when a full-scale analog input voltage

of 9.990 volts (10 volts—1 LSB) is applied at the input. The in-

put resistor is trimmed in this way so that if a fine trimming po-

tentiometer is inserted in series with the input signal, the input

current at the full-scale input voltage can be trimmed down to

match the DAC full-scale current as precisely as desired. How-

ever, for many applications the nominal 9.99 volt full scale can

be achieved to sufficient accuracy by simply inserting a 15

Ω re-

sistor in series with the analog input to Pin 13. Typical full-scale

calibration error will then be about

±2 LSB or ±0.2%. If a more

precise calibration is desired, a 50

Ω trimmer should be used in-

stead. Set the analog input at 9.990 volts, and set the trimmer

so that the output code is just at the transition between

1111111110 and 1111111111. Each LSB will then have a weight

of 9.766 mV. If a nominal full scale of 10.24 volts is desired

(which makes the LSB have a value of exactly 10.00 mV), a

100

Ω resistor in series with a 100 Ω trimmer (or a 200 Ω trim-

mer with good resolution) should be used. Of course, larger

full-scale ranges can be arranged by using a larger input resistor,

but linearity and full-scale temperature coefficient may be com-

promised if the external resistor becomes a sizable percentage

of 5 k

Ω.

BIT 9

BIT 8

BIT 10 (LSB)

DATA READY

BIT 5

BIT 4

BIT 3

ANALOG IN

–15V

BIT 7

BIT 6

DIGITAL COM

BIT 2

BLK AND

CONV

(MSB) BIT 1

ANALOG COM

BIPOLAR CONTROL

1

2

18

17

5

6

7

14

13

12

3

4

16

15

8

11

9

10

TOP VIEW

(Not to Scale)

AD571

+5V

(TOLERATES 200mV TO

DIGITAL COM)

15

Ω FIXED OR

50

Ω VARIABLE

(SEE TEXT)

(SHORT TO COM FOR

UNIPOLAR, OPEN FOR BIPOLAR)

Figure 4. Standard AD571 Connections

BIPOLAR OPERATION

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

ing the bipolar offset control pin to digital common. If the pin is

left open, the bipolar offset current will be switched into the

comparator summing node, giving a –5 V to +5 V range with an

offset binary output code. (–5.00 volts in will give a 10-bit code

of 0000000000; an input of 0.00 volts results in an output code of

1000000000 and 4.99 volts at the input yields the 1111111111).

The bipolar offset control input is not directly TTL compatible,

but a TTL interface for logic control can be constructed as

shown in Figure 5.

AD571

B & C

DR

DATA

BIPOLAR

OFFSET

CONTROL

TTL

GATE

10 BITS

5V COM

+5V

15V COM

30k

Ω

3x IN4148

USE ACTIVE

PULL-UP GATE

–15V

Figure 5. Bipolar Offset Controlled by Logic Gate

Gate Output = 1: Unipolar 0 V–10 V Input Range

Gate Output = 0: Bipolar

±5 V Input Range

COMMON-MODE RANGE

The AD571 provides separate analog and digital common con-

nections. The circuit will operate properly with as much as

±200 mV of common-mode range between the two commons.

This permits more flexible control of system common bussing

and digital and analog returns.

In normal operation the analog common terminal may generate

transient currents of up to 2 mA during a conversion. In addi-

tion, a static current of about 2 mA will flow into analog com-

mon in the unipolar mode after a conversion is complete. An

additional 1 mA will flow in during a blank interval with zero

analog input. The analog common current will be modulated by

the variations in input signal.

The absolute maximum voltage rating between the two com-

mons is

±1 volt. We recommend that a parallel pair of back-to-

back protection diodes can be connected between the commons

if they are not connected locally.

TEMPERATURE –

°C

11

3

–50

125

–25

0

25

50

70

100

10

7

6

5

4

9

8

2

1.5

1

I +15V,C

I –15V,B

I –15V,C

I +15V,B

I +5V,C

I +5V,B

C = CONVERT MODE

B = BLANK MODE

Figure 6. AD571 Power Supply Current vs. Temperature