AD586 datasheet(46/48 Pages) AD

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AD5735

Data Sheet

Rev. B | Page 46 of 48

DRIVING INDUCTIVE LOADS

When driving inductive or poorly defined loads, a capacitor

may be required between the IOUT_x pin and the AGND pin to

ensure stability. A 0.01 µF capacitor between IOUT_x and AGND

ensures stability of a load of 50 mH. The capacitive component

of the load may cause slower settling, although this may be

masked by the settling time of the AD5735. There is no maxi-

mum capacitance limit for the current output of the AD5735.

TRANSIENT VOLTAGE PROTECTION

The AD5735 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 AD5735 from excessively high voltage transients,

external power diodes and a surge current limiting resistor (RP)

are required, as shown in Figure 83. A typical value for RP is 10 Ω.

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

priate power ratings.

RLOAD

AD5735

VBOOST_x

IOUT_x

AGND

CDCDC

4.7µF

CFILTER

0.1µF

RFILTER

Ω

(FROM

DC-TO-DC

CONVERTER)

Figure 83. 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.

The voltage output node can be protected with a similar circuit,

where D2 and the transorb are connected to AVSS. For the volt-

age output node, the +VSENSE_x pin should also be protected with

a large value series resistance to the transorb, such as 5 kΩ. In

this way, the IOUT_x and VOUT_x pins can also be tied together and

share the same protection circuitry.

MICROPROCESSOR INTERFACING

Microprocessor interfacing to the AD5735 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 AD5735 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.

AD5735-to-ADSP-BF527 Interface

The AD5735 can be connected directly to the SPORT interface

of the ADSP-BF527, an Analog Devices, Inc., Blackfin® DSP.

Figure 84 shows how the SPORT interface can be connected

to control the AD5735.

AD5735

SYNC

SCLK

SDIN

LDAC

SPORT_TFS

SPORT_TSCLK

SPORT_DT0

GPIO0

ADSP-BF527

Figure 84. AD5735-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 AD5735 is mounted should be designed so that the

analog and digital sections are separated and confined to

certain areas of the board. If the AD5735 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 AD5735 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 capac-

itors are the tantalum bead type. The 0.1 µF capacitors 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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