AD5689 datasheet(23/24 Pages) AD

23 / 24 page

Data Sheet

AD5689/AD5687

Rev. B | Page 23 of 24

APPLICATIONS INFORMATION

MICROPROCESSOR INTERFACING

Microprocessor interfacing to the AD5689/AD5687 is achieved

via a serial bus using a standard protocol that is compatible with

DSP processors and microcontrollers. The communications

channel requires a 3-wire or 4-wire interface consisting of a clock

signal, a data signal, and a synchronization signal. Each device

requires a 24-bit data-word with data valid on the rising edge

of SYNC.

AD5689/AD5687 TO ADSP-BF531 INTERFACE

The SPI interface of the AD5689/AD5687 is designed to be

easily connected to industry-standard DSPs and microcontrollers.

Figure 43 shows the AD5689/AD5687 connected to an Analog

Devices Blackfin® DSP. The Blackfin has an integrated SPI port

that connects directly to the SPI pins of the AD5689/AD5687.

ADSP-BF531

SYNC

SPISELx

SCLK

SCK

SDIN

MOSI

LDAC

PF9

RESET

PF8

AD5689/

AD5687

Figure 43. ADSP-BF531 Interface to the AD5689/AD5687

AD5689/AD5687 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 AD5689/AD5687.

ADSP-BF527

SYNC

SPORT_TFS

SCLK

SPORT_TSCK

SDIN

SPORT_DTO

LDAC

GPIO0

RESET

GPIO1

AD5689/

AD5687

Figure 44. SPORT Interface to the AD5689/AD5687

LAYOUT GUIDELINES

In any circuit where accuracy is important, careful consideration of

the power supply and ground return layout helps to ensure the

rated performance. Design the PCB on which the AD5689/

AD5687 are mounted so that the AD5689/AD5687 lie on the

analog plane.

Provide the AD5689/AD5687 with 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 capacitor is of the tantalum bead type. Use a 0.1 μF capa-

citor with 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.

Each AD5689 or AD5687 has 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 45) to provide a natural heat sinking effect.

AD5689/

AD5687

GND

PLANE

BOARD

Figure 45. Paddle Connection to Board

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. The

iCoupler® products from Analog Devices provide voltage

isolation in excess of 2.5 kV. The serial loading structure of the

AD5689/AD5687 makes these parts ideal for isolated interfaces

because the number of interface lines is kept to a minimum.

Figure 46 shows a 4-channel isolated interface to the AD5689/

AD5687 using an ADuM1400. For more information, visit

www.analog.com/icouplers.

ENCODE

SERIAL

CLOCK IN

CONTROLLER

ADuM14001

SERIAL

DATA OUT

SYNC OUT

LOAD DAC

OUT

DECODE

SCLK

SDIN

SYNC

LDAC

VIA

VOA

ENCODE

DECODE

VIB

VOB

ENCODE

DECODE

VIC

VOC

ENCODE

DECODE

VID

VOD

1ADDITIONAL PINS OMITTED FOR CLARITY.

Figure 46. Isolated Interface

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