Datasheet

EVAL-AD7400A/AD7401A
Rev. 0 | Page 6 of 16
SOCKETS
There are 4 SMB input sockets relevant to the operation of the
AD7400A or AD7401A on this evaluation board. All of these
sockets are used for applying an externally generated signal to
the evaluation board. When operating the board with the EVAL-
CED1Z, the only external sockets necessary are those used to
supply the differential input signals to the analog inputs of the
ADC (that is, J2 (V
IN
+), J3 (V
IN
−)). All of the other sockets are
optional and if they are not used, their signals are supplied by
the EVAL-CED1Z. Most of these sockets are used when operat-
ing the board as a standalone unit, as all the signals required are
supplied from external sources. The functions of these sockets
are outlined in Table 4.
The V
DD1
supply, which is the supply for the isolated side of
the device, must be supplied by an external source via the J1-1
connector. The V
DD2
supply must be supplied by 3.3 V from an
external source via the J4 connector.
Table 4. Socket Functions
Socket Function
J2 (V
IN
+)
Subminiature BNC socket for a unipolar
differential input that is applied directly to the
V
IN
+ pin of the AD7400A or AD7401A.
J3 (V
IN
−)
Subminiature BNC socket for a unipolar
differential input that is applied directly to the
V
IIN
− pin of the AD7400A or AD7401A.
J5 (MCLKOUT/
MCLKIN)
Subminiature BNC socket for the MCLKOUT
output on the AD7400A or subminiature BNC
socket for the MCLKIN input to the AD7401A.
J6 (MDAT) Subminiature BNC socket for the MDAT output.
CONNECTORS
There are three connectors on the EVAL-AD7400A/AD7401A
as outlined in Table 5.
Table 5. Connector Functions
Connector Function
J1-1 External V
DD1
power connector.
J1-2 External GND
1
power connector.
J1-3 External −5 V power connector.
J4-1 External V
DD2
power connector.
J4-2 GND
2
power connector.
J12
SPORT connector for the digital interface and
power supply connections.
TEST POINTS
There are numerous test points on the EVAL-AD7400A/
AD7401A. The test points enable the user to have easy access
to these signals for probing, evaluation, and debugging.
OPERATING WITH THE EVAL-CED1Z
The evaluation board can be operated in standalone mode
or operated in conjunction with the EVAL-CED1Z. This
evaluation board controller is available from Analog Devices
under the order entry EVAL-CED1Z.
When interfacing the EVAL-AD7400A/AD7401A directly to
the EVAL-CED1Z, the control signals to operate the EVAL-
AD7400A/AD7401A are provided by the EVAL-CED1Z. The
device supplies (V
DD1
, V
DD2
, and −5 V) need to be supplied
by an external source via the J1 and J4 connectors. If the
AD797 op amps are not being used, then the −5 V is not
required.
The AD7400A and AD7401A are isolated Σ-Δ modulators
that convert an analog input signal into a high speed (10 MHz
typical for AD7400A and 20 MHz for the AD7401A), single-
bit data stream. The time average of the single-bit data from
the modulator is directly proportional to the input signal. To
generate an output digital word similar to a conventional ADC,
the 1 bit output data stream from the AD7400A or AD7401A
needs to be processed by a digital filter. A sinc3 filter is recom-
mended for use with a decimation rate of 256, this results in a
16-bit word with a throughout rate of 39 kHz, assuming a 10 MHz
clock frequency. The sinc3 filter has been implemented in the
FPGA on the EVAL-CED1Z and hence the performance results
displayed by the software are generated using this filter with a
decimation rate of 256.
For the AD7401A the MCLKIN is supplied by the EVAL-
CED1Z. The MSCLK frequency is set at 16 MHz. This gives
a throughput rate of 62.5 kSPS for a decimation rate of 256.
The software allows the user to change the throughput rate
by effectively modifying the decimation rate.
Software to communicate with the EVAL-CED1Z and the
AD7400A or AD7401A is provided with the EVAL-AD7400A/
AD7401A package.
The SPORT connector on the EVAL-AD7400A/AD7401A
plugs directly into the SPORT connector on the EVAL-CED1Z
board. The EVAL-CED1Z board is powered from a 7 V, 15 W
power supply which accepts input voltages from 100 V to 240 V
ac and contains the relevant adaptors for worldwide use. The
power supply is provided with the EVAL-CED1Z.
Connection between the EVAL-CED1Z and the USB port of a
PC is via a standard USB 2.0 connection cable that is provided
as part of the EVAL-CED1Z package.