AD5686R datasheet(28/31 Pages) AD

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AD5686R/AD5685R/AD5684R

Data Sheet

Rev. D | Page 28 of 31

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 59 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 59. ADSP-BF531 Interface

AD5686R/AD5685R/AD5684R TO SPORT

INTERFACE

The Analog Devices ADSP-BF527 has one SPORT serial port.

Figure 60 shows how one SPORT interface can be used to

control the AD5686R/AD5685R/AD5684R.

Figure 60. 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 61) to provide a natural heat sinking effect.

Figure 61. Paddle Connection to Board

ADSP-BF531

SYNC

SPISELx

SCLK

SCK

SDIN

MOSI

LDAC

PF9

RESET

PF8

AD5686R/

AD5685R/

AD5684R

ADSP-BF527

SYNC

SPORT_TFS

SCLK

SPORT_TSCK

SDIN

SPORT_DTO

LDAC

GPIO0

RESET

GPIO1

AD5686R/

AD5685R/

AD5684R

AD5686R/

AD5685R/

AD5684R

GND

PLANE

BOARD

AD5686R Datasheet(PDF) 28 Page - Analog Devices

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