AD565A/AD566A

REV. D

–9–

CONNECTING THE AD566A FOR BUFFERED VOLTAGE

OUTPUT

The standard current-to-voltage conversion connections using

an operational amplifier are shown here with the preferred trim-

ming techniques. If a low offset operational amplifier (AD510L,

AD517L, AD741L, AD301AL, AD OP07) is used, excellent

performance can be obtained in many situations without trim-

ming (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

will typically be within

±1/2 LSB (plus op amp offset), and full

scale accuracy will be within 0.1% (0.25% max). Substituting a

50

Ω resistor for the 100 Ω bipolar offset trimmer will give a

bipolar zero error typically within

±2 LSB (0.05%).

The AD509 is recommended for buffered voltage-output appli-

cations which require a settling time to

±1/2 LSB of one micro-

second. The feedback capacitor is shown with the optimum

value for each application; this capacitor is required to compen-

sate for the 25 picofarad DAC output capacitance.

FIGURE 4. UNIPOLAR CONFIGURATION

This configuration will provide a unipolar 0 volt to +10 volt

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 volts (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 volts. (Full scale is adjusted to 1 LSB less than

nominal full scale of 10.000 volts.) 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 will provide a bipolar output voltage from

–5.000 volts to +4.9976 volts, 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 volts.

STEP II . . . GAIN ADJUST

Turn ON all bits. Adjust 100

Ω gain trimmer R2 to give a read-

ing of +4.9976 volts.

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.