Data Sheet AD5601/AD5611/AD5621
Rev. H | Page 19 of 21
USING THE AD5601/AD5611/AD5621 WITH A
GALVANICALLY ISOLATED INTERFACE
In process control applications in industrial environments,
it is often necessary to use a galvanically isolated interface to
protect and isolate the controlling circuitry from any hazardous
common-mode voltages that might occur in the area where the
DAC is functioning. iCoupler® provides isolation in excess of
2.5 kV. Because the AD5601/AD5611/AD5621 use a 3-wire serial
logic interface, the ADuM1300 3-channel digital isolator
provides the required isolation (see Figure 53). The power
supply to the part also needs to be isolated, which is done by
using a transformer. On the DAC side of the transformer, a 5 V
regulator provides the 5 V supply required for the AD5601/
AD5611/AD5621.
Figure 53. AD5601/AD5611/AD5621 with a Galvanically Isolated Interface
POWER SUPPLY BYPASSING AND GROUNDING
When accuracy is important in a circuit, it is helpful to carefully
consider the power supply and ground return layout on the
board. The PCB containing the AD5601/AD5611/AD5621
should have separate analog and digital sections, each having its
own area of the board. If the AD5601/AD5611/AD5621 are in a
system where other devices require an AGND-to-DGND
connection, the connection should be made at one point only.
This ground point should be as close as possible to the
AD5601/AD5611/AD5621.
The power supply to the AD5601/AD5611/AD5621 should be
bypassed with 10 μF and 0.1 μF capacitors. The capacitors
should be physically as close as possible to the device, with the
0.1 μF capacitor ideally right up against the device. The 10 μF
capacitors are the tantalum bead type. It is important that the
0.1 μF capacitor have low effective series resistance (ESR) and
effective series inductance (ESI), such as in common ceramic
types of capacitors. This 0.1 μF capacitor provides a low imped-
ance path to ground for high frequencies caused by transient
currents due to internal logic switching.
The power supply line itself should have as large a trace as
possible to provide a low impedance path and reduce glitch
effects on the supply line. Clocks and other fast switching
digital signals should be shielded from other parts of the board
by digital ground. Avoid crossover of digital and analog signals,
if possible. When traces cross on opposite sides of the board,
ensure that they run at right angles to each other to reduce
feedthrough effects on the board. The best board layout tech-
nique is the microstrip technique, where the component side of
the board is dedicated to the ground plane only and the signal
traces are placed on the solder side. However, this is not always
possible with a two-layer board.
06853-052
V
DD
AD5601/
AD5611/
AD5621
ADuM1300
POWER 10µF 0.1µF
GND
5V
REGULATOR
SCLKV
OA
V
OUT
V
OB
SYNC
V
OC
V
IA
V
IB
V
IC
SCLK
SDI
DATA SDIN
