AD767 Datasheet PDF - Analog Devices
| Part Number | AD767 | |
| Description | Microprocessor-Compatible 12-Bit D/A Converter | |
| Manufacturers | Analog Devices | |
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FEATURES
Complete 12-Bit D/A Function
On-Chip Output Amplifier
High Stability Buried Zener Reference
Fast 40 ns Write Pulse
0.3" Skinny DIP and PLCC Packages
Single Chip Construction
Monotonicity Guaranteed Over Temperature
Settling Time: 3 s max to 1/2 LSB
Guaranteed for Operation with ؎12 V or ؎15 V Supplies
TTL/5 V CMOS Compatible Logic Inputs
MIL-STD-883 Compliant Versions Available
Microprocessor-Compatible
12-Bit D/A Converter
AD767*
FUNCTIONAL BLOCK DIAGRAM
PRODUCT DESCRIPTION
The AD767 is a complete voltage output 12-bit digital-to-
analog converter including a high stability buried Zener
reference and input latch on a single chip. The converter uses
12 precision high-speed bipolar current steering switches and a
laser-trimmed thin-film resistor network to provide high accuracy.
Microprocessor compatibility is achieved by the on-chip latch.
The design of the input latch allows direct interface to 12-bit
buses. The latch responds to strobe pulses as short as 40 ns,
allowing use with the fastest available microprocessors.
The functional completeness and high performance of the
AD767 result from a combination of advanced switch design,
high-speed bipolar manufacturing process, and the proven laser
wafer-trimming (LWT) technology.
The subsurface (buried) Zener diode on the chip provides a
low-noise voltage reference which has long-term stability and
temperature drift characteristics comparable to the best discrete
reference diodes. The laser trimming process which provides the
excellent linearity is also used to trim the absolute value of the
reference as well as its temperature coefficient. The AD767 is
thus well suited for wide temperature range performance with
± 1/2 LSB maximum linearity error and guaranteed monotonicity
over the full temperature range. Typical full-scale gain T.C. is
5 ppm/°C.
PRODUCT HIGHLIGHTS
1. The AD767 is a complete voltage output DAC with voltage
reference and digital latches on a single IC chip.
2. The input latch responds to write pulse widths as short as
40 ns assuring direct interface with the industry’s fastest
microprocessors.
3. The internal buried Zener reference is laser-trimmed to
10.00 volts with a ± 1% maximum error. The reference
voltage is also available for external application.
4. The gain setting and bipolar offset resistors are matched to
the internal ladder network to guarantee a low gain temperature
coefficient and are laser trimmed for minimum full-scale and
bipolar offset errors.
5. The precision high-speed current steering switches and
on-board high-speed output amplifier settle within 1/2 LSB
for a 10 V full-scale transition in 3.0 µs when properly
compensated.
6. The AD767 is available in versions compliant with
MIL-STD-883. Refer to the Analog Devices Military
Products Databook or current AD767/883B data sheet for
detailed specifications.
*Protected by Patent Numbers 3,803,590; 3,890,611; 3,932,863; 3,978,473;
4,020,486; and others pending.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
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AD767
BIPOLAR CONFIGURATION (Figure 3)
This configuration will provide a bipolar output voltage from
–5.000 to +4.9976 volts, with positive full scale occurring with
all bits ON (all 1s).
STEP I … OFFSET ADJUST
Turn OFF all bits. Adjust 100 Ω trimmer R1 to give –5.000
volts output.
STEP II … GAIN ADJUST
Turn ON all bits. Adjust 100 Ω gain trimmer R2 to give a
reading of +4.9976 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 R1 for zero volts
output.
Figure 3. ±5 V Bipolar Voltage Output
INTERNAL/EXTERNAL REFERENCE USE
The AD767 has an internal low-noise buried Zener diode
reference which is trimmed for absolute accuracy and tempera-
ture coefficient. This reference is buffered and optimized for use
in a high-speed DAC and will give long-term stability equal or
superior to the best discrete Zener reference diodes. The per-
formance of the AD767 is specified with the internal reference
driving the DAC since all trimming and testing (especially for
full-scale error and bipolar offset) is done in this configuration.
The internal reference has sufficient buffering to drive external
circuitry in addition to the reference currents required for the
DAC (typically 0.5 mA to Ref In and 1.0 mA to Bipolar Offset).
A minimum of 0.1 mA is available for driving external loads.
The AD767 reference output should be buffered with an
external op amp if it is required to supply more than 0.1 mA
output current. The reference is typically trimmed to ± 0.2%,
then tested and guaranteed to ± 1.0% max error. The
temperature coefficient is comparable to that of the full-scale
TC for a particular grade.
If an external reference is used (10.000 V, for example),
additional trim range must be provided, since the internal
reference has a tolerance of ± 1%, and the AD767 full-scale and
bipolar offset are both trimmed with the internal reference. The
gain and offset trim resistors give about ± 0.25% adjustment
range, which is sufficient for the AD767 when used with the
internal reference.
It is also possible to use external references other than 10 volts.
The recommended range of reference voltage is from +8 to
+10.5 volts, which allows both 8.192 V and 10.24 V ranges to
be used. The AD767 is optimized for fixed-reference applications.
If the reference voltage is expected to vary over a wide range in
a particular application, a CMOS multiplying DAC is a better
choice.
Reduced values of reference voltage will also permit the ± 12 volt
± 5% power supply requirement to be relaxed to ± 12 volts
± 10%.
It is not recommended that the AD767 be used with external
feedback resistors to modify the scale factor. The internal
resistors are trimmed to ratio-match and temperature-track the
other resistors on the chip, even though their absolute tolerances
are ±20%, and absolute temperature coefficients are approximately
–50 ppm/°C. If external resistors are used, a wide trim range
(± 20%) will be needed and temperature drift will be increased
to reflect the mismatch between the temperature coefficients of
the internal and external resistors.
Small resistors may be added to the feedback resistors in order
to accomplish small modifications in the scaling. For example, if
a 10.24 V full scale is desired, a 140 Ω 1% low-TC metal-film
resistor can be added in series with the internal (nominal) 5k
feedback resistor, and the gain trim potentiometer (between
Pins 6 and 7) should be increased to 200 Ω. In the bipolar
mode, increase the value of the bipolar offset trim potentiometer
also to 200 Ω.
REV. A
Figure 4. Using the AD767 with the AD588 High Precision Reference
–5–
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| Information | Total 8 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
| Download | [ AD767.PDF Datasheet ] | |
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