EVAL-AD5765EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD5765EBZ' PDF : 28 Pages View PDF
AD5765
LAYOUT GUIDELINES
For any circuit in which accuracy is important, careful consid-
eration of the power supply and ground return layout helps to
ensure the rated performance. The printed circuit board on
which the AD5765 is mounted should be designed so that the
analog and digital sections are separated and confined to
certain areas of the board. If the AD5765 is in a system in which
multiple devices require an AGND-to-DGND connection, the
connection should be made at one point only. The star ground
point should be established as close as possible to the device.
The AD5765 should 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 capa-
citor should 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 AD5765 should use 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, should be shielded with digital ground
to avoid radiating noise to other parts of the board and should
never be run near the reference inputs. A ground line routed
between the SDIN and SCLK lines helps reduce crosstalk
between them (this is 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 such noise couples through to the DAC output.
Avoid crossover of digital and analog signals. Traces on
opposite sides of the board should 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.
Isocouplers provide voltage isolation in excess of 2.5 kV. The
serial loading structure of the AD5765 makes it ideal for
Data Sheet
isolated interfaces because the number of interface lines is kept
to a minimum. Figure 30 shows a 4-channel isolated interface to
the AD5765 using an ADuM1400. For more information, go to
www.analog.com.
MICRO-
CONTROLLER
SERIAL CLOCK
OUT
ADuM14001
VIA
ENCODE
SERIAL DATA VIB
OUT
ENCODE
SYNC OUT VIC
ENCODE
DECODE
DECODE
DECODE
VOA
TO SCLK
VOB
TO SDIN
VOC
TO SYNC
CONTROL OUT VID
ENCODE
DECODE
VOD
TO LDAC
1ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 30. Isolated Interface
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5765 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 AD5765 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 done
automatically when all the data is clocked in, or it can be done
under the control of LDAC. The contents of the DAC register
can be read using the readback function.
AD5765 to Blackfin DSP Interface
Figure 31 shows how the AD5765 can be interfaced to an Analog
Devices, Inc., Blackfin® DSP. The Blackfin has an integrated SPI
port that can be connected directly to the SPI pins of the AD5765
and programmable I/O pins that can be used to set the state of a
digital input such as the LDAC pin.
ADSP-BF531
SPISELx
SCK
MOSI
PF10
AD57651
SYNC
SCLK
SDIN
LDAC
1ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 31. AD5765 to Blackfin Interface
Rev. C | Page 26 of 28
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