AD565A

REV.

–8–

CONNECTING THE AD565A FOR BUFFERED VOLTAGE

OUTPUT

The standard current-to-voltage conversion connections using an

operational amplifier are shown in Figures 1, 2, and 3 with the

preferred trimming techniques. If a low offset operational amplifier

(OP77, AD741L, OP07) is used, excellent performance can be

obtained in many situations without trimming (an op amp with

less than 0.5 mV max offset voltage should be used to keep offset

errors below 1/2 LSB). If a 50

Ω fixed resistor is substituted for

the 100

Ω trimmer, unipolar zero is typically within ±1/2 LSB

(plus op amp offset) and full-scale accuracy is within 0.1%

(0.25% max). Substituting a 50

Ω resistor for the 100 Ω bipo-

lar offset trimmer gives a bipolar zero error typically within

±2 LSB (0.05%).

The AD509 is recommended for buffered voltage-output

applications that require a settling time to

± 1/2 LSB of

1

μs. The feedback capacitor is shown with the optimum value

for each application; this capacitor is required to compen-

sate for the 25 pF DAC output capacitance.

FIGURE 1. UNIPOLAR CONFIGURATION

This configuration provides a unipolar 0 V to 10 V output

range. In this mode, the bipolar terminal, Pin 8, should be

grounded if not used for trimming.

19.95k

20k

0.5mA

DAC

4

CODE

AD565A

9.95k

5k

8k

20V SPAN

10V SPAN

DAC

OUT

POWER

GND

REF

GND

BIPOLAR OFF

5k

CODE

INPUT

LSB

MSB

10V

REF

OUT

REF

IN

R2

100

10pF

AD509

OUTPUT

0V TO

+10V

100

100k

+15V

–15V

R1

50k

2.4k

Figure 1. 0 V to 10 V Unipolar Voltage Output

STEP I . . . ZERO ADJUST

Turn all bits OFF and adjust zero trimmer R1 until the output

reads 0.000 V (1 LSB = 2.44 mV). In most cases, this trim is not

needed, but Pin 8 should then be connected to Pin 12.

STEP II . . . GAIN ADJUST

Turn all bits ON and adjust 100

Ω gain trimmer R2 until the

output is 9.9976 V. (Full scale is adjusted to 1 LSB less than

nominal full scale of 10.000 V.) If a 10.2375 V full scale is desired

(exactly 2.5 mV/bit), insert a 120

Ω resistor in series with the gain

resistor at Pin 10 to the op amp output.

FIGURE 2. BIPOLAR CONFIGURATION

This configuration provides a bipolar output voltage from

–5.000 V to +4.9976 V, with positive full scale occurring with

all bits ON (all 1s).

19.95k

20k

0.5mA

DAC

4

CODE

AD565A

9.95k

5k

8k

20V SPAN

10V SPAN

DAC

OUT

POWER

GND

REF

GND

BIPOLAR OFF

5k

CODE

INPUT

LSB

MSB

10V

REF

OUT

REF

IN

R2

100

10pF

AD509

OUTPUT

–5V TO

+5V

2.4k

R1

100

Figure 2.

±5 V Bipolar Voltage Output

STEP I . . . OFFSET ADJUST

Turn OFF all bits. Adjust 100

Ω trimmer R1 to give –5.000 V

output.

STEP II . . . GAIN ADJUST

Turn ON all bits. Adjust 100

Ω gain trimmer R2 to give a

reading of +4.9976 V.

Please note that it is not necessary to trim the op amp to obtain

full accuracy at room temperature. In most bipolar situations,

an op amp trim is unnecessary unless the untrimmed offset drift

of the op amp is excessive.

FIGURE 3. OTHER VOLTAGE RANGES

The AD565A can also be easily configured for a unipolar 0 V to

+5 V range or

±2.5 V and ±10 V bipolar ranges by using the

additional 5 k

Ω application resistor provided at the 20 V span R

terminal, Pin 11. For a 5 V span (0 V to +5 V, or

±2.5 V), the

two 5 k

Ω resistors are used in parallel by shorting Pin 11 to Pin 9

and connecting Pin 10 to the op amp output and the bipolar

offset either to ground for unipolar or to REF OUT for the

bipolar offset either to ground for unipolar or to REF OUT for

the bipolar range. For the

±10 V range (20 V span) use the 5 kΩ

resistors in series by connecting only Pin 11 to the op amp output

and the bipolar offset connected as shown. The

±10 V option is

shown in Figure 3.

19.95k

20k

0.5mA

DAC

4

CODE

AD565A

9.95k

5k

8k

20V SPAN

10V SPAN

DAC

OUT

POWER

GND

REF

GND

BIPOLAR OFF

5k

CODE

INPUT

LSB

MSB

10V

REF

OUT

REF

IN

R2

100

10pF

AD509

OUTPUT

–10V TO

+10V

3.0k

R1

100

Figure 3.

±10 V Voltage Output

F