REV.

–9–

CONNECTING THE AD566A FOR BUFFERED VOLTAGE

OUTPUT

The standard current-to-voltage conversion connections using an

operational amplifier are shown in Figures 4, 5, and 6 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 typically is 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 bipolar 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 compensate for the

25 pF DAC output capacitance.

FIGURE 4. UNIPOLAR CONFIGURATION

This configuration provides a unipolar 0 V to 10 V output range.

In this mode, the bipolar terminal, Pin 7, should be grounded if not

used for trimming.

100k

+15V

–15V

R1

50k

19.95k

20k

0.5mA

DAC

4

CODE

AD566A

9.95k

5k

8k

20V SPAN

10V SPAN

DAC

OUT

POWER

GND

REF

GND

BIPOLAR OFF

5k

CODE

INPUT

LSB

MSB

R2

100

10pF

AD509

2.4k

100

AD561

+V

REF

IN

Figure 4. 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 7 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 5. 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

AD566A

9.95k

5k

8k

20V SPAN

10V SPAN

DAC

OUT

POWER

GND

REF

GND

BIPOLAR OFF

5k

CODE

INPUT

LSB

MSB

R2

100

10pF

AD509

2.4k

AD561

+V

REF

IN

R1

100

Figure 5.

±5 V Bipolar Voltage Output

STEP I . . . OFFSET ADJUST

Turn OFF all bits. Adjust 100

Ω trimmer R1 to give –5.000

output V.

STEP II . . . GAIN ADJUST

Turn ON all bits. Adjust 100

Ω gain trimmer R2 to give a read-

ing 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.

F

AD565A