Datasheet

AD5696/AD5694 Data Sheet
Rev. A | Page 22 of 24
APPLICATIONS INFORMATION
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5696/AD5694 is via a
serial bus that uses a standard protocol that is compatible with
DSP processors and microcontrollers. The communications
channel requires a 2-wire interface consisting of a clock signal
and a data signal.
AD5696/AD5694 TO ADSP-BF531 INTERFACE
The I
2
C interface of the AD5696/AD5694 is designed for easy
connection to industry-standard DSPs and microcontrollers.
Figure 41 shows the AD5696/AD5694 connected to the Analog
Devices, Inc., Blackfin® processor. The Blackfin processor has
an integrated I
2
C port that can be connected directly to the I
2
C
pins of the AD5696/AD5694.
Figure 41. AD5696/AD5694 to ADSP-BF531 Interface
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. The PCB on which the AD5696/AD5694
are mounted should be designed so that the AD5696/AD5694
lie on the analog plane.
The AD5696/AD5694 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 capacitor is 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; these
capacitors provide a low impedance path to ground at high
frequencies to handle transient currents due to internal logic
switching.
In systems where many devices are on one board, it is often
useful to provide some heat sinking capability to allow the
power to dissipate easily.
The AD5696/AD5694 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 LFCSP 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 42) to provide a natural heat sinking effect.
Figure 42. 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 Analog Devices iCoupler® products provide voltage iso-
lation in excess of 2.5 kV. The serial loading structure of the
AD5696/AD5694
makes the part ideal for isolated interfaces
because the number of interface lines is kept to a minimum.
Figure 43 shows a 4-channel isolated interface to the AD5696/
AD5694 using the ADuM1400. For more information, visit
http://www.analog.com/icouplers.
Figure 43. Isolated Interface
ADSP-BF531
SCLGPIO1
SDAGPIO2
LDACPF9
RESETPF8
AD5696/
AD5694
10799-164
AD5696/
AD5694
GND
PLANE
BOARD
10799-166
ENCODE
SERIAL
CLOCK IN
CONTROLLER
ADuM1400
SERIAL
DATA OUT
RESET OUT
LOAD DAC
OUT
DECODE
TO
SCL
TO
SDA
TO
RESET
TO
LDAC
V
IA
V
OA
ENCODE
DECODE
V
IB
V
OB
ENCODE DECODE
V
IC
V
OC
ENCODE DECODE
V
ID
V
OD
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