Datasheet

AD5755-1 Data Sheet
Rev. E | Page 48 of 52
Traces
The power supply lines of the AD5755-1 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 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 oppo-
site sides of the board should run at right angles to each other.
This reduces the effects of feedthrough on 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, whereas 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 80):
• 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 L
DCDC
and the
rectifier, D
DCDC
, to 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
COMP
DCDC_x
.
• 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 AD5755-
1 makes it ideal for isolated interfaces because the number of
interface lines is kept to a minimum. Figure 88 shows a 4-
channel isolated interface to the AD5755-1 using an
ADuM1400. For more information, visit www.analog.com.
09226-081
V
IA
SERIAL CLOCK
OUT
TO SCLK
V
OA
ENCODE
DECODE
V
IB
SERIAL DATA
OUT
TO SDIN
V
OB
ENCODE
DECODE
V
IC
SYNC OUT
V
OC
ENCODE
DECODE
V
ID
CONTROL OUT
V
OD
ENCODE
DECODE
MICROCONTROLLER
ADuM1400*
*ADDITIONAL PINS OMITTED FOR CLARITY.
TO SYNC
TO LDAC
Figure 88. Isolated Interface