AD660SQ/883B AD [Analog Devices], AD660SQ/883B Datasheet - Page 7

• Manufacturer Part Number: AD660SQ/883B
• Description: Monolithic 16-Bit Serial/Byte DACPORT
• Manufacturer: AD [Analog Devices]

BIPOLAR CONFIGURATION
The circuit shown in Figure 4a will provide a bipolar output
voltage from –10.000000 V to +9.999694 V with positive full
scale occurring with all bits ON. As in the unipolar mode, resis-
tors R1 and R2 may be eliminated altogether to provide AD660
bipolar operation without any external components. Eliminat-
ing these resistors will increase the gain error by 0.50% of FSR
in the bipolar mode.
Gain offset and bipolar zero errors can be adjusted to zero us-
ing the circuit shown in Figure 4b as follows:
STEP I . . . OFFSET ADJUST
Turn OFF all bits. Adjust trimmer R2 to give 10.000000 volts
output.
STEP II . . . GAIN ADJUST
Turn all bits ON and adjust R1 to give a reading of +9.999694
volts.
STEP III . . . BIPOLAR ZERO ADJUST (Optional)
In applications where an accurate zero output is required, set
the MSB ON, all other bits OFF, and readjust R2 for zero volts
output.
Figure 4b.
Offset Adjustment
REV. A
R1 50
LDAC
100
R1
HBE
SER
CLR
HBE
SER
CLR
16
17
18
19
23
16
17
18
19
23
Figure 4a.
UNI/BIP CLR/
UNI/BIP CLR/
REF IN
REF IN
LDAC
LBE
CONTROL
LBE
10 V Bipolar Voltage Output with Gain and
CONTROL
15
15
LOGIC
LOGIC
REF OUT
REF OUT
CS
14
CS
14
10k
10k
+10V REF
+10V REF
R2 50
10 V Bipolar Voltage Output
SIN/
DB0
SIN/
DB0
24
24
12
12
16-BIT LATCH
16-BIT LATCH
16-BIT LATCH
16-BIT LATCH
R2
100
16-BIT DAC
16-BIT DAC
MSB/LSB/
DB1
MSB/LSB/
DB1
11
11
–V
–V
1
1
EE
EE
DB7
DB7
5
+V
5
+V
2
2
CC
CC
+V
+V
AD660
AD660
3
3
10.05k
LL
LL
10.05k
10k
10k
DGND
DGND
4
4
13
22
20
21
13
22
20
21
SPAN/
BIP OFF
V
S
SPAN/
BIP OFF
V
S
AGND
OUT
OUT
OUT
OUT
OUTPUT
OUTPUT
AGND
–7–
It should be noted that using external resistors will introduce a
small temperature drift component beyond that inherent in the
AD660. The internal resistors are trimmed to ratio-match and
temperature-track other resistors on chip, even though their ab-
solute tolerances are 20% and absolute temperature coeffi-
cients are approximately –50 ppm/ C . In the case that external
resistors are used, the temperature coefficient mismatch be-
tween internal and external resistors, multiplied by the sensitiv-
ity of the circuit to variations in the external resistor value, will
be the resultant additional temperature drift.
INTERNAL/EXTERNAL REFERENCE USE
The AD660 has an internal low noise buried Zener diode refer-
ence which is trimmed for absolute accuracy and temperature
coefficient. This reference is buffered and optimized for use in a
high speed DAC and will give long-term stability equal or supe-
rior to the best discrete Zener diode references. The perfor-
mance of the AD660 is specified with the internal reference
driving the DAC and with the DAC alone (for use with a preci-
sion external reference ).
The internal reference has sufficient buffering to drive external
circuitry in addition to the reference currents required for the
DAC (typically 1 mA to REF IN and 1 mA to BIPOLAR
OFFSET). A minimum of 2 mA is available for driving external
loads. The AD660 reference output should be buffered with an
external op amp if it is required to supply more than 4 mA total
current. The reference is tested and guaranteed to 0.2% max
error.
It is also possible to use external references other than 10 volts
with slightly degraded linearity specifications. The recom-
mended range of reference voltages is +5 V to +10.24 V, which
allows 5 V, 8.192 V and 10.24 V ranges to be used. For ex-
ample, by using the AD586 5 V reference, outputs of 0 V to
+5 V unipolar or 5 V bipolar can be realized. Using the
AD586 voltage reference makes it possible to operate the
AD660 with 12 V supplies with 10% tolerances.
AD660