AD5764CSUZ Datasheet, PDF (27/28 Pages) Analog Devices – Complete Quad, 16-Bit, High Accuracy, Serial Input, Bipolar Voltage Output DAC

Data Sheet
LAYOUT GUIDELINES
In any circuit where accuracy is important, careful consideration
of the power supply and ground return layout helps to ensure the
rated performance. The PCB on which the AD5764 is mounted
must be designed so that the analog and digital sections are sepa-
rated and confined to certain areas of the board. If the AD5764 is
in a system where multiple devices require an AGND-to-DGND
connection, the connection is to be made at one point only. The
star ground point is established as close as possible to the device.
The AD5764 must have ample supply bypassing of 10 μF in parallel
with 0.1 μF on each supply, located as close to the package as
possible, ideally right up against the device. The 10 μF capacitors
are the tantalum bead type. The 0.1 μF capacitor must have low
effective series resistance (ESR) and low effective series inductance
(ESI), such as the common ceramic types, which provide a low
impedance path to ground at high frequencies to handle transient
currents due to internal logic switching.
The power supply lines of the AD5764 must be as large a trace
as possible to provide low impedance paths and reduce the effects
of glitches on the power supply line. Fast switching signals, such as
clocks, must be shielded with digital ground to avoid radiating
noise to other parts of the board, and must never be run near
the reference inputs. A ground line routed between the SDIN
and SCLK lines helps reduce crosstalk between them (not required
on a multilayer board, which has a separate ground plane; however,
it is helpful to separate the lines). It is essential to minimize noise
on the reference inputs because it couples through to the DAC
output. Avoid crossover of digital and analog signals. Traces on
opposite sides of the board must run at right angles to each other.
This reduces the effects of feedthrough on the board. A microstrip
technique is recommended, but not always possible with a double-
sided board. In this technique, the component side of the board
is dedicated to the ground plane, and signal traces are placed on
the solder side.
GALVANICALLY ISOLATED INTERFACE
In many process control applications, it is necessary to provide
an isolation barrier between the controller and the unit being
controlled to protect and isolate the controlling circuitry from
any hazardous common-mode voltages that may occur. Isocoup-
lers provide voltage isolation in excess of 2.5 kV. The serial
loading structure of the AD5764 makes it ideal for isolated
AD5764
interfaces because the number of interface lines is kept to a
minimum. Figure 37 shows a 4-channel isolated interface to the
AD5764 using an ADuM1400. For more information, go to
www.analog.com.
MICROCONTROLLER
SERIAL CLOCK
OUT
ADuM1400*
V_IA
ENCODE
SERIAL DATA ^VIB
OUT
ENCODE
SYNC OUT ^VIC
ENCODE
DECODE
DECODE
DECODE
V_OA
TO SCLK
V_OB
TO SDIN
V_OC
TO SYNC
CONTROL OUT ^VID
ENCODE
DECODE
V_OD
TO LDAC
*ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 37. Isolated Interface
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5764 is via a serial bus
that uses a standard protocol that is compatible with micro-
controllers and DSP processors. The communications channel
is a 3-wire (minimum) interface consisting of a clock signal, a
data signal, and a synchronization signal. The AD5764 requires
a 24-bit data-word with data valid on the falling edge of SCLK.
For all the interfaces, the DAC output update can be performed
automatically when all the data is clocked in, or it can be done
under the control of LDAC. The contents of the data register
can be read using the readback function.
EVALUATION BOARD
The AD5764 comes with a full evaluation board to aid designers
in evaluating the high performance of the part with minimum
effort. All that is required with the evaluation board is a power
supply and a PC. The AD5764 evaluation kit includes a populated,
tested AD5764 PCB. The evaluation board interfaces to the USB
port of the PC. Software is available with the evaluation board,
which allows the user to easily program the AD5764. The software
runs on any PC that has Microsoft® Windows® 2000/NT/XP
installed.
The EVAL-AD5764EB data sheet is available, which gives full
details on the operation of the evaluation board.
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