AD5641 Analog Devices, AD5641 Datasheet - Page 17

• Manufacturer Part Number: AD5641
• Description: 2.7 V to 5.5 V,
• Manufacturer: Analog Devices

Specifications of AD5641

• Resolution (bits): 14bit
• Dac Update Rate: 1.7MSPS
• Dac Settling Time: 6µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

Data Sheet
USING THE AD5641 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. The AD5641 use a 3-wire serial logic interface, so the
ADuM1300
isolation (see Figure 45). 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 AD5641.
SCLK
DATA
POWER
SDI
Figure 45. AD5641 with a Galvanically Isolated Interface
VIA
VIB
VIC
three-channel digital isolator provides the required
ADuM1300
VOA
VOB
VOC
REGULATOR
5V
SCLK
SYNC
SDIN
AD5641
GND
V
DD
V
10µF
OUT
0.1µF
Rev. D | Page 17 of 20
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 printed circuit board containing the AD5641 should
have separate analog and digital sections, each having its own
area of the board. If the AD5641 is 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 AD5641.
The power supply to the AD5641 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
has 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 impedance
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
technique 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 2-layer board.
AD5641