AD586 datasheet(40/44 Pages) AD

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AD5737

Data Sheet

Rev. B | Page 40 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 (RP)

are required, as shown in Figure 62. A typical value for RP is 10 Ω.

The two protection diodes and the resistor (RP) must have appro-

priate power ratings.

RLOAD

AD5737

VBOOST_x

IOUT_x

AGND

CDCDC

4.7µF

CFILTER

0.1µF

RFILTER

Ω

(FROM

DC-TO-DC

CONVERTER)

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

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 GNDSWx pin and the ground connection for the AVCC

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.

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