AD5755 datasheet(33/34 Pages) AD

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Preliminary Technical Data

AD5755/AD5735

Rev. PrG | Page 33 of 34

Figure 22. AD5755/AD5735 to ADSP-BF527 SPORT 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 printed circuit board on which the

AD5755/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 AD5755/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 AD5755/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 capacitors are 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, which provide a low impedance path to ground

at high frequencies to handle transient currents due to internal

logic switching.

The power supply lines of the AD5755/AD5735 should use as

large a trace as possible to provide low impedance paths and

reduce the effects of glitches on the power supply line. Fast

switching signals such as clocks should be shielded with digital

ground to avoid radiating noise to other parts of the board and

should never be run near the reference inputs. A ground line

routed between the SDIN and SCLK lines helps reduce crosstalk

between them (not required on a multilayer board that has a

separate ground plane, but separating the lines helps). It is

essential to minimize noise on the REFIN line because it

couples through to the DAC output.

Avoid crossover of digital and analog signals. Traces on

opposite sides of the board should run at right angles to each

other. This reduces the effects of feed through the board. A

microstrip technique is by far the best, but not always possible

with a double-sided board. In this technique, the component

side of the board is dedicated to ground plane, while signal

traces are placed on the solder side.

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 might occur.

Isocouplers provide voltage isolation in excess of 2.5 kV. The

serial loading structure of the AD5755/AD5735 makes it ideal

for isolated interfaces, because the number of interface lines is

kept to a minimum. Figure 23 shows a 4-channel isolated

interface to the AD5755/AD5735 using an ADuM1400. For

more information, go to www.analog.com.

Figure 23. Isolated Interface

VIA

SERIAL CLOCK OUT

TO SCLK

VOA

ENCODE

DECODE

VIB

SERIAL DATA OUT

TO SDIN

VOB

ENCODE

DECODE

VIC

SYNC OUT

TO SYNC

VOC

ENCODE

DECODE

VID

CONTROL OUT

TO LDAC

VOD

ENCODE

DECODE

µCONTROLLER

ADuM14001

1ADDITIONAL PINS OMITTED FOR CLARITY

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