AD586 datasheet(47/48 Pages) AD

47 / 48 page

Data Sheet

AD5735

Rev. B | Page 47 of 48

Traces

The power supply lines of the 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 prevent radi-

ating 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 traces 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 oppo-

site sides of the board should run at right angles to each other

to reduce the effects of feedthrough on the board. A microstrip

technique is by far the best method, but it is not always possible

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

side of the board is dedicated to ground plane, and signal traces

are placed on the solder side.

DC-to-DC Converters

To achieve high efficiency, good regulation, and stability, a

well-designed printed circuit board layout is required.

Follow these guidelines when designing printed circuit boards

(see Figure 77):

•

Keep the low ESR input capacitor, CIN, close to AVCC and

PGND.

•

Keep the high current path from CIN through the inductor

(LDCDC) to SWx and PGND as short as possible.

•

Keep the high current path from CIN through the inductor

(LDCDC), the diode (DDCDC), and the output capacitor

(CDCDC) as short as possible.

•

Keep high current traces as short and as wide as possible.

The path from CIN through the inductor (LDCDC) to SWx

and PGND should be able to handle a minimum of 1 A.

•

Place the compensation components as close as possible to

the COMPDCDC_x pin.

•

Avoid routing high impedance traces near any node

connected to SWx or near the inductor to prevent radiated

noise injection.

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 can provide voltage isolation

in excess of 2.5 kV. The serial loading structure of the AD5735

makes it ideal for isolated interfaces because the number of inter-

face lines is kept to a minimum. Figure 85 shows a 4-channel

isolated interface to the AD5735 using an ADuM1411. For

more information, visit www.analog.com.

VIA

SERIAL CLOCK

OUT

TO SCLK

VOA

ENCODE

DECODE

VIB

SERIAL DATA

OUT

TO SDIN

VOB

ENCODE

DECODE

VIC

SYNC OUT

VOC

ENCODE

DECODE

VID

CONTROL OUT

VOD

ENCODE

DECODE

MICROCONTROLLER

ADuM1411

TO SYNC

TO LDAC

Figure 85. 4-Channel Isolated Interface to the AD5735

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