AD664
Figure 1a. 44-Pin Block Diagram
FUNCTIONAL DESCRIPTION
tions. This register may also be read back to check its contents.
A RESET-TO-ZERO feature allows all DACs to be reset to 0
volts out by strobing a single pin.
The AD664 combines four complete 12-bit voltage output D/A
converters with a fast, flexible digital input/output port on one
monolithic chip. It is available in two forms, a 44-pin version
shown in Figure 1a and a 28-pin version shown in Figure 1b.
44-Pin Versions
Each DAC offers flexibility, accuracy and good dynamic perfor-
mance. The R-2R structure is fabricated from thin-film resistors
which are laser-trimmed to achieve 1/2 LSB linearity and guar-
anteed monotonicity. The output amplifier combines the best
features of the bipolar and MOS devices to achieve good dy-
namic performance and low offset. Settling time is under 10 µs
and each output can drive a 5 mA, 500 pF load. Short-circuit
protection allows indefinite shorts to VLL, VCC, VEE and GND.
The output and span resistor pins are available separately. This
feature allows a user to insert current-boosting elements to in-
crease the drive capability of the system, as well as to overcome
parasitics.
Digital circuitry is implemented in CMOS logic. The fast, low
power, digital interface allows the AD664 to be interfaced with
most microprocessors. Through this interface, the wide variety
of features on each chip may be accessed. For example, the in-
put data for each DAC is programmed by way of 4-, 8-, 12- or
16-bit words. The double-buffered input structure of this latch
allows all four DACs to be updated simultaneously. A readback
feature allows the internal registers to be read back through the
same digital port, as either 4-, 8- or 12-bit words. When dis-
abled, the readback drivers are placed in a high impedance
(tristate) mode. A TRANSPARENT mode allows the input data
to pass straight through both ranks of input registers and appear
at the DAC with a minimum of delay. One D/A may be placed
in the transparent mode at a time, or all four may be made
transparent at once. The MODE SELECT feature allows the
output range and mode of the DACs to be selected via the data
bus inputs. An internal mode select register stores the selec-
Figure 1b. 28-Pin Block Diagram
28-Pin Versions
The 28-pin versions are dedicated versions of the 44-pin
AD664. Each offers a reduced set of features from those offered
in the 44-pin version. This accommodates the reduced number
of package pins available. Data is written and read with 12-bit
words only. Output range and mode select functions are also
not available in 28-pin versions. As an alternative, users specify
either the UNI (unipolar, 0 to VREF) models or the BIP (bipolar,
–VREF to VREF) models depending on the application require-
ments. Finally, the transparent mode is not available on the
28-pin versions.
D
REV.
–4–
ADI [ ADI ]
