AD565A/AD566A
CONNECTING THE AD566A FOR BUFFERED VOLTAGE
OUTPUT
FIGURE 5. BIPOLAR CONFIGURATION
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 bipolar output voltage from
–5.000 volts to +4.9976 volts, with positive full scale occurring
with all bits ON (all 1s).
R1
100
BIPOLAR OFF
20V SPAN
9.95k
5k
5k
AD566A
10V SPAN
R2
100
REF
IN 19.95k
10pF
0.5mA
I
REF
I
O
8k
DAC
OUT
AD509
2.4k
+V
10V
E
REF
DAC
I
OUT
=
4 I
REF
CODE
CODE
INPUT
MSB
LSB
AD561
REF
GND
20k
POWER
GND
–V
EE
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.
+15V
100
100k
BIPOLAR OFF
R1
50k
–15V
20V SPAN
9.95k
5k
5k
R2
100
+V
10V
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
AD566A
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.
10V SPAN
REF
IN 19.95k
E
REF
AD561
REF
GND
POWER
GND
–V
EE
10pF
0.5mA
I
REF
I
O
8k
DAC
OUT
AD509
2.4k
DAC
I
OUT
=
4 I
REF
CODE
CODE
INPUT
MSB
LSB
20k
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.
REV. D
–9–
AD [ ANALOG DEVICES ]
