EVAL-AD7716EB Datasheet, PDF (2/12 Pages) Analog Devices – Evaluation Board For 22-Bit Data Acquisition System

EVAL-AD7716EB
HARDWARE DESCRIPTION
The circuit diagram for the EVAL-AD7716EB is shown in
Figure 1. The circuit is powered by +/- 5V supplies which are
connected to V_DD and V_SS. All analog and digital circuitry on
the board is powered from these supplies.
Analog Section
The OP-07 input buffers are low noise, low-bandwidth op-amps
and are ideal for buffering the low-bandwidth signals which the
AD7716 will digitise. They have a specified noise spectral
density of 11nV/Root Hz at 600Hz. This corresponds to an rms
noise of 0.25µV in the band, which is more than adequate for
the AD7716.
The AD780 reference is the recommended reference for these
low-noise applications. It provides the necessary +2.5V
reference for the device. It is chosen for its very low noise in the
programmed passband. The AD780 has a typical noise spectral
density of 100nV/Root Hz at 600 Hz. This corresponds to an
rms noise of 2.5µV in this band, which is more than adequate
for the AD7716.
Digital Section
The AD7716 will accept one digital input to the D_IN1 pin and
allow transmission back to the host processor. The D_IN1 input
is clearly identified at P1 on the board.
The device also allows the user to program two digital outputs.
These outputs are available on D_OUT1 and D_OUT2 and the state
of these output is displayed on the two LED’s, D1 and D2.
Note that D_OUT1 and D_OUT2 are also available on P1.
The EVAL-AD7716EB has an on-board 8Mhz crystal oscillator
to run the device. This is a standard parallel resonance crystal
and has two 15pF capacitors connected for stable operation.
On the digital side of the AD7716, the circuitry is designed to
simplify the printer port interface. The SDATA pin of the
device is separated into two (SDATAIN AND SDATAOUT).
The DRDY output pin is used as the handshake signal for the
printer port.
CASCIN and CASCOUT are made available on J2. These
signals allow multiple AD7716’s to be hooked together simply in
multi-device applications.
Links and Switches
There are a number of links and switches on the board and their
functions are described below.
LK1:
Normally Not Connected. This link connects
the CASCOUT pin to the CASCIN pin of the
AD7716. When the device is operated in this
fashion, a reset must be applied after every write
to the control register.
LK2:
Normally Connected. This link connects the
inverse of DRDY to the CASCIN pin of the
AD7716. When used in this fashion, only one
reset is needed at the start of operation is
needed. The control register may be written to
without further resets.
LK3:
Normally Not Connected. This link allows
IC8 to be bypassed in applications where the
user wishes to keep a common SDATA line.
LK4:
Normally Not Connected. This link, in
association with LK14, allows IC8 to be
bypassed.
SW2-1:
SW2-2,3,4:
This switch when positioned as in Figure 2, sets
the MODE pin of the AD7716 to a "high".
This sets up the device for the Slave Mode
Interface, which is the interface mode employed
when connected to the PC. In this mode, the
AD7716 is the slave in the system and the
processor is the master.
These three switches,when positioned as in
Figure 2, set the device address pins A0, A1, A2
of the AD7716 to "000", respectively. This
information is contained in the data stream
going back to the processor. In a multi-device
system, it is possible to have eight discrete
addresses for eight AD7716, thus making a 32-
channel data acquisition system. Please consult
the AD7716 data sheet for further details.
1
1
1
234
0
0
Figure 2. SW2 Default Settings
–2–
REV. B