AD1674
GRO UND ING
P ACKAGE INFO RMATIO N
If a single AD1674 is used with separate analog and digital
ground planes, connect the analog ground plane to AGND and
the digital ground plane to DGND keeping lead lengths as short
as possible. T hen connect AGND and DGND together at the
AD1674. If multiple AD1674s are used or the AD1674 shares
analog supplies with other components, connect the analog and
digital returns together once at the power supplies rather than at
each chip. T his prevents large ground loops which inductively
couple noise and allow digital currents to flow through the ana-
log system.
D imensions shown in inches and (mm).
28-P in Ceram ic D IP P ackage (D -28)
0.505 (12.83)
28
15
0.59 ±0.01
(14.98 ±0.254)
PIN 1
14
1
GENERAL MICRO P RO CESSO R INTERFACE
CO NSID ERATIO NS
0.050 ±0.010
(1.27 ±0.254)
0.095
(2.41)
1.42 (36.07)
1.40 (35.56)
A typical A/D converter interface routine involves several opera-
tions. First, a write to the ADC address initiates a conversion.
T he processor must then wait for the conversion cycle to com-
plete, since most ADCs take longer than one instruction cycle to
complete a conversion. Valid data can, of course, only be read
after the conversion is complete. T he AD1674 provides an out-
put signal (ST S) which indicates when a conversion is in
progress. T his signal can be polled by the processor by reading
it through an external three-state buffer (or other input port).
T he ST S signal can also be used to generate an interrupt upon
completion of a conversion, if the system timing requirements
are critical (bear in mind that the maximum conversion time of
the AD1674 is only 10 microseconds) and the processor has
other tasks to perform during the ADC conversion cycle. An-
other possible time-out method is to assume that the ADC will
take 10 microseconds to convert, and insert a sufficient number
of “no-op” instructions to ensure that 10 microseconds of pro-
cessor time is consumed.
0.145 ±0.02
(3.68 ±0.51)
0.125
(3.17)
MIN
0.010 ±0.002
(0.254 ±0.05)
0.085
(2.16)
0.6 (15.24)
SEATING
PLANE
0.047 ±0.007
(1.19 ±0.178)
0.1 (2.54)
0.017 ±0.003
(0.43 ±0.076)
28-Lead P lastic D IP P ackage (N-28)
28
1
15
0.550 (13.97)
0.530 (13.462)
PIN 1
14
0.606 (15.39)
0.594 (15.09)
1.450 (38.83)
1.440 (35.576)
0.160 (4.06)
0.140 (3.56)
0.200
(5.080)
MAX
15
°
0.012 (0.305)
0.008 (0.203)
0°
0.175 (4.45)
0.105 (2.67)
0.065 (1.65)
0.045 (1.14)
0.020 (0.508)
0.015 (0.381)
0.120 (3.05)
SEATING
PLANE
0.095 (2.41)
Once it is established that the conversion is finished, the data
can be read. In the case of an ADC of 8-bit resolution (or less),
a single data read operation is sufficient. In the case of convert-
ers with more data bits than are available on the bus, a choice of
data formats is required, and multiple read operations are
needed. T he AD1674 includes internal logic to permit direct in-
terface to 8-bit or 16-bit data buses, selected by the 12/8 input.
In 16-bit bus applications (12/8 HIGH) the data lines (DB11
through DB0) may be connected to either the 12 most signifi-
cant or 12 least significant hits of the data bus. T he remaining
four bits should be masked in software. T he interface to an 8-bit
data bus (12/8 LOW) contains the 8 MSBs (DB11 through
DB4). T he odd address (A0 HIGH) contains the 4 LSBs (DB3
through DB0) in the upper half of the byte, followed by four
trailing zeroes, thus eliminating bit masking instructions.
28-Lead Wide-Body SO P ackage (R-28)
28
15
0.2992 (7.60)
0.2914 (7.40)
0.4193 (10.65)
PIN 1
0.3937 (10.00)
14
1
0.1043 (2.65)
0.7125 (18.10)
0.0926 (2.35)
0.6969 (17.70)
0.0291 (0.74)
x 45°
0.0098 (0.25)
0.0500 (1.27)
0.0157 (0.40)
8°
0°
0.0118 (0.30)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
0.0500 (1.27)
BSC
0.0125 (0.32)
0.0091 (0.23)
AD1674 Data Form at for 8-Bit Bus
–12–
REV. C
ADI [ ADI ]
