Datasheet

Data Sheet AD5737
Rev. C | Page 41 of 44
TRANSIENT VOLTAGE PROTECTION
The AD5737 contains ESD protection diodes that prevent dam-
age from normal handling. The industrial control environment
can, however, subject I/O circuits to much higher transients. To
protect the AD5737 from excessively high voltage transients,
external power diodes and a surge current limiting resistor (R
P
)
are required, as shown in Figure 62. A typical value for R
P
is 10 Ω.
The two protection diodes and the resistor (R
P
) must have appro-
priate power ratings.
R
LOAD
R
D1
D2
P
AD5737
V
BOOST_x
I
OUT_x
AGND
C
DCDC
4.7µF
C
FILTER
0.1µF
R
FILTER
10Ω
(FROM
DC-TO-DC
CONVERTER)
10067-079
Figure 62. Output Transient Voltage Protection
Further protection can be provided using transient voltage
suppressors (TVSs), also referred to as transorbs. These compo-
nents are available as unidirectional suppressors, which protect
against positive high voltage transients, and as bidirectional
suppressors, which protect against both positive and negative
high voltage transients. Transient voltage suppressors are avail-
able in a wide range of standoff and breakdown voltage ratings.
The TVS should be sized with the lowest breakdown voltage
possible while not conducting in the functional range of the
current output.
It is recommended that all field connected nodes be protected.
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5737 is via a serial bus
that uses a protocol compatible with microcontrollers and DSP
processors. The communication channel is a 3-wire minimum
interface consisting of a clock signal, a data signal, and a latch
signal. The AD5737 requires a 24-bit data-word with data valid
on the falling edge of SCLK.
The DAC output update is initiated either on the rising edge of
LDAC
or, if
LDAC
is held low, on the rising edge of
SYNC
. The
contents of the registers can be read using the readback function.
AD5737-to-ADSP-BF527 Interface
The AD5737 can be connected directly to the SPORT interface
of the ADSP-BF527, an Analog Devices, Inc., Blackfin® DSP.
Figure 63 shows how the SPORT interface can be connected
to control the AD5737.
AD5737
SYNC
SCLK
SDIN
LDAC
SPORT_TFS
SPORT_TSCLK
SPORT_DT0
GPIO0
ADSP-BF527
10067-080
Figure 63. AD5737-to-ADSP-BF527 SPORT Interface
LAYOUT GUIDELINES
Grounding
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 printed circuit board on
which the AD5737 is mounted should be designed so that the
analog and digital sections are separated and confined to
certain areas of the board. If the AD5737 is in a system where
multiple devices require an AGND-to-DGND connection, the
connection should be made at one point only. The star ground
point should be established as close as possible to the device.
The GNDSW
x
pin and the ground connection for the AV
CC
supply are referred to as PGND. PGND should be confined to
certain areas of the board, and the PGND-to-AGND connection
should be made at one point only.
Supply Decoupling
The AD5737 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 cap-
acitors should have low effective series resistance (ESR) and low
effective series inductance (ESL), 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.