Datasheet

AD5686/AD5684 Data Sheet
Rev. A | Page 24 of 28
APPLICATIONS INFORMATION
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5686/AD5684 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
.
AD5686/AD5684 TO ADSP-BF531 INTERFACE
The SPI interface of the AD5686/AD5684 is designed to be
easily connected to industry-standard DSPs and micro-
controllers. Figure 43 shows the AD5686/AD5684 connected
to the Analog Devices, Inc., Blackfin® DSP. The Blackfin has an
integrated SPI port that can be connected directly to the SPI
pins of the AD5686/AD5684.
Figure 43. ADSP-BF531 Interface
AD5686/AD5684 TO SPORT INTERFACE
The Analog Devices ADSP-BF527 has one SPORT serial
port. Figure 44 shows how one SPORT interface can be used
to control the AD5686/AD5684.
Figure 44. 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 AD5686/
AD5684 are mounted should be designed so that the AD5686/
AD5684 lie on the analog plane.
The AD5686/AD5684 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 AD5686/AD5684 LFCSP models have an exposed pad
beneath the device. Connect this pad 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 pad on the bottom of the package to the
corresponding thermal land pad on the PCB. Design thermal
vias into the PCB land pad area to further improve heat
dissipation.
The GND plane on the device can be increased (as shown in
Figure 45) to provide a natural heat sinking effect.
Figure 45. Pad Connection to Board
ADSP-BF531
SYNCSPISELx
SCLK
SCK
SDINMOSI
LDACPF9
RESETPF8
AD5686/
AD5684
10797-164
ADSP-BF527
SYNCSPORT_TFS
SCLKSPORT_TSCK
SDINSPORT_DTO
LDACGPIO0
RESETGPIO1
AD5686/
AD5684
10797-165
AD5686/
AD5684
GND
PLANE
BOARD
10797-166