Datasheet

AD5686R/AD5685R/AD5684R Data Sheet
Rev. B | Page 28 of 32
APPLICATIONS INFORMATION
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5686R/AD5685R/
AD5684R is via a serial bus that uses a standard protocol that
is compatible with DSP processors and microcontrollers.
The communications channel requires a 3- or 4-wire interface
consisting of a clock signal, a data signal, and a synchronization
signal. The devices require a 24-bit data-word with data valid
on the rising edge of
SYNC
.
AD5686R/AD5685R/AD5684R TO ADSP-BF531
INTERFACE
The SPI interface of the AD5686R/AD5685R/AD5684R is
designed to be easily connected to industry-standard DSPs and
microcontrollers. Figure 60 shows the AD5686R/AD5685R/
AD5684R connected to the Analog Devices Blackfin® DSP. The
Blackfin has an integrated SPI port that can be connected
directly to the SPI pins of the AD5686R/AD5685R/AD5684R.
Figure 60. ADSP-BF531 Interface
AD5686R/AD5685R/AD5684R TO SPORT
INTERFACE
The Analog Devices ADSP-BF527 has one SPORT serial port.
Figure 61 shows how one SPORT interface can be used to
control the AD5686R/AD5685R/AD5684R.
Figure 61. SPORT Interface
LAYOUT GUIDELINES
In any circuit where accuracy is important, careful consider-
ation of the power supply and ground return layout helps to
ensure the rated performance. The PCB on which the AD5686R/
AD5685R/AD5684R are mounted should be designed so that
the AD5686R/AD5685R/AD5684R lie on the analog plane.
The AD5686R/AD5685R/AD5684R 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 capacitor 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.
In systems where there are many devices on one board, it is
often useful to provide some heat sinking capability to allow
the power to dissipate easily.
The AD5686R/AD5685R/AD5684R have an exposed paddle
beneath the device. Connect this paddle to the GND supply for
the part. For optimum performance, use special considerations
to design the motherboard and to mount the package. For
enhanced thermal, electrical, and board level performance,
solder the exposed paddle on the bottom of the package to the
corresponding thermal land paddle on the PCB. Design thermal
vias into the PCB land paddle area to further improve heat
dissipation.
The GND plane on the device can be increased (as shown in
Figure 62) to provide a natural heat sinking effect.
Figure 62. Paddle Connection to Board
ADSP-BF531
SYNCSPISELx
SCLKSCK
SDINMOSI
LDACPF9
RESETPF8
AD5686R/
AD5685R/
AD5684R
10485-164
ADSP-BF527
SYNCSPORT_TFS
SCLKSPORT_TSCK
SDINSPORT_DTO
LDACGPIO0
RESETGPIO1
AD5686R/
AD5685R/
AD5684R
10485-165
AD5686R/
AD5685R/
AD5684R
GND
PLANE
BOARD
10485-166