AD7871TQ Analog Devices Inc, AD7871TQ Datasheet - Page 13

• Manufacturer Part Number: AD7871TQ
• Description: IC ADC 14BIT SAMPLING 28-CDIP
• Manufacturer: Analog Devices Inc

Specifications of AD7871TQ

• Rohs Status: RoHS non-compliant
• Number Of Bits: 14
• Sampling Rate (per Second): 83k
• Data Interface: Serial, Parallel
• Number Of Converters: 1
• Power Dissipation (max): 95mW
• Voltage Supply Source: Dual ±
• Operating Temperature: -55°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: 28-CDIP (0.600", 15.24mm)

LAYOUT HINTS
Ensure that the layout for the printed circuit board has the digi-
tal and analog signal lines separated as much as possible. Take
care not to run a digital track alongside an analog signal track.
Guard (screen) the analog input with AGND.
Establish a single point analog ground (star ground) separate
from the logic system ground at the AD7871/AD7872 AGND
pin or as close as possible to the AD7871/AD7872. Connect all
other grounds and the AD7871/AD7872 DGND to this single
analog ground point. Do not connect any other digital grounds
to this analog ground point.
Low impedance analog and digital power supply common re-
turns are essential to low noise operation of the ADC, so make
the foil width for these tracks as wide as possible. The use of
ground planes minimizes impedance paths and also guards the
analog circuitry from digital noise. The circuit layout of Figures
26 and 27 have both analog and digital ground planes that are
kept separated and joined together only at the AD7871/AD7872
AGND pin.
NOISE
Keep the input signal leads to V
AGND as short as possible to minimize input noise coupling. In
applications where this is not possible, use a shielded cable be-
tween the source and the ADC. Reduce the ground circuit im-
pedance as much as possible since any potential difference in
grounds between the signal source and the ADC appears as an
error voltage in series with the input signal.
DATA ACQUISITION BOARD
Figure 24 shows the AD7871/AD7872 in a data acquisition cir-
cuit. The corresponding printed circuit board (PCB) layout has
three interface ports: one serial and two parallel. Note that the
AD7871/AD7872 serial lines are buffered by a 74HC244. This
allows long lines with large capacitive loads to be driven. One of
the parallel ports is directly compatible with the ADSP-2100
evaluation board expansion connector.
The only additional component required for a full data acquisi-
tion system is an anti-aliasing filter. There is a component grid
provided near the analog input on the PCB, which may be used
for such a filter or any other input conditioning circuitry. To fa-
cilitate this option, there is a shorting plug (labelled LK1 on the
PCB) on the analog input track. If this shorting plug is used, the
analog input connects to the buffer amplifier driving the AD7871/
AD7872; if this shorting plug is omitted, a wire link can be used to
connect the analog input to the PCB component grid.
INTERFACE CONNECTIONS
There are two parallel connectors labeled SKT4 and SKT6,
and one serial connector labeled SKT5. A shorting plug option
(LK3 in Figure 24) configures the ADC for the appropriate
interface.
SKT6 is a 96-contact (3-row) Eurocard connector that is directly
compatible with the ADSP-2100 Evaluation Board Prototype
Expansion Connector. The expansion connector on the
ADSP-2100 has eight decoded chip enable outputs labeled
ECE1 to ECE8. ECE6 is used to drive the AD7871 CS input
on the board. To avoid selecting the onboard RAM sockets at
the same time, LK6 on the ADSP-2100 board must be removed.
In addition, the ADSP-2100 expansion connector has four in-
REV. D
IN
and signal return leads from
–13–
terrupts labelled EIRQ0 to EIRQ3. The AD7871 BUSY/INT
output connects to EIRQ0. There is a single wait state generator
connected to EDMACK to allow the AD7871 to interface to the
faster versions of the ADSP-2100.
SKT4 is a 26-way (2-row) IDC connector. This contains the
same signal contacts as SKT6 except for EDMACK, which is
connected to SKT6 only. It also contains decoded R/W and
STRB inputs necessary for TMS32020 interfacing.
SKT5 is a 5-way D-type connector meant for serial interfacing
only. An inverted DB11/SCLK output is also provided on this
connector for systems that accept data on a rising clock edge.
SKT1, SKT2 and SKT3 are three BNC connectors providing
connections for the analog input, the CONVST input and an
external clock.
Figure 22. SKT4 Pinout
POWER SUPPLY CONNECTIONS
The PCB requires two analog power supplies and one 5 V logic
supply. The analog supplies are labelled V+ and V–, and the
range for both supplies is 12 V to 15 V. Connection to the 5 V
digital supply is made through any of the connectors SKT4 to
SKT6. The 5 V supply required by the AD7871 and AD7872
is generated from voltage regulators on the V+ and V– power
supplies input (IC6 and IC7 in Figure 24).
SHORTING PLUG OPTIONS
There are seven shorting plug options which must be set before
using the board. These are outlined below:
LK1 Connects the analog input to a buffer amplifier. The
LK2 Selects either the AD7871/AD7872 internal clock or
LK3 Configures the AD7871 14/8/CLK input for the
LK4 Connects the AD7871 RD input directly to the two par-
LK5 Connects the pull-up resistor R3 to SSTRB.
LK6 Connects the pull-up resistor R4 to SCLK.
LK7 Connects the pull-up resistor R5 to SDATA.
Note that LK5 to LK7 should be removed for parallel interfacing.
analog input may also be connected to a component
grid for signal conditioning.
an external clock source.
appropriate serial or parallel interface.
allel connectors or to a decoded STRB and R/W input.
Figure 23. SKT5 Pinout
AD7871/AD7872