Datasheet

Data Sheet AD5735
Rev. C | 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, C
IN
, close to AV
CC
and
PGND.
• Keep the high current path from C
IN
through the inductor
(L
DCDC
) to SW
x
and PGND as short as possible.
• Keep the high current path from C
IN
through the inductor
(L
DCDC
), the diode (D
DCDC
), and the output capacitor
(C
DCDC
) as short as possible.
• Keep high current traces as short and as wide as possible.
The path from C
IN
through the inductor (L
DCDC
) to SW
x
and PGND should be able to handle a minimum of 1 A.
• Place the compensation components as close as possible to
the COMP
DCDC_x
pin.
• Avoid routing high impedance traces near any node
connected to SW
x
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.
V
IA
SERIAL
CLOCK
OUT
TO SCLK
V
O
A
ENCODE
DECODE
V
IB
SERIA
L D
AT
A
OUT
T
O SDIN
V
OB
ENCODE DECODE
V
IC
SYNC OUT
V
OC
ENCODE DECODE
V
ID
CONTROL
OUT
V
OD
ENCODE DECODE
MICROCONTROLLER
ADuM1411
T
O SYNC
TO LDAC
09961-081
Figure 85. 4-Channel Isolated Interface to the AD5735