AD5686 datasheet(24/28 Pages) AD

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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

SYNC

SPISELx

SCLK

SCK

SDIN

MOSI

LDAC

PF9

RESET

PF8

AD5686/

AD5684

ADSP-BF527

SYNC

SPORT_TFS

SCLK

SPORT_TSCK

SDIN

SPORT_DTO

LDAC

GPIO0

RESET

GPIO1

AD5686/

AD5684

AD5686/

AD5684

GND

PLANE

BOARD

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