AD5726
Data Sheet
Rev. C | Page 16 of 20
Single 5V SupplyOperation
For operation with a 5 V supply, the reference voltage should
be set between 1.0 V and 2.5 V for optimum linearit
y. Figure 28shows a
n AD780 used to supply a 2.5 V reference voltage. The
headroom of the reference and DAC are both sufficient to support
a +5 V supply with ±5 V tolerance.
06469-
026
5V
10F
0.01F
INPUT
OUTPUT
GND
TRIM
0.2F
AD780
AD5726
AVDD
5V
AVSS
GND
VREFP
VREFN
0V TO 2.5V OPERATION
SINGLE 5V SUPPLY
10kΩ
0.1F║10F
Figure 28. 5 V Single-Supply Operation
POWER SUPPLY BYPASSING AND GROUNDING
In any circuit where accuracy is important, careful consideration
to the power supply and ground return layout helps to ensure
the rated performance. Th
e AD5726 has a single ground pin
that is internally connected to the digital section as the logic
reference level. The user’s first instinct may be to connect this
pin to the digital ground; however, in large systems, the digital
ground is often noisy because of the switching currents of other
digital circuitry. Any noise introduced at the ground pin could
couple into the analog output. Thus, to avoid error-causing
digital noise in the sensitive analog circuitry, the ground pin
should be connected to the system analog ground.
The ground path (circuit board trace) should be as wide as possible
to reduce any effects of parasitic inductance and ohmic drops. A
ground plane is recommended if possible. The noise immunity
of the on-board digital circuitry, typicallyin the hundreds of milli-
volts, is well able to reject the common-mode noise typically seen
between system analog and digital grounds. Finally, connect the
analog and digital ground to each other at a single point in the
system to provide a common reference. This connection is prefer-
ably done at the power supply.
Good grounding practice is essential to maintain analog perform-
ance in the surrounding analog support circuitry as well. With
two reference inputs and four analog outputs capable of moderate
bandwidth and output current, there is a significant potential
for ground loops. Again, a ground plane is recommended as
the most effective solution to minimize errors due to noise and
ground offsets.
Th
e AD5726 should have ample supply bypassing located as
close to the package as possible. Recommended capacitor values
are 10 F in parallel with 0.1 F. The 0.1 F capacitor should
have low effective series resistance (ESR) and effective series
inductance (ESI), such as the common ceramic types, which
provide a low impedance path to ground at high frequencies
to handle transient currents due to internal logic switching.
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 fromany
hazardous common-mode voltages that may occur. Isocouplers
provide voltage isolation in excess of 2.5 kV. The serial loading
structure of th
e AD5726 makes it ideal for isolated interfaces
because the number of interface lines is kept to a minimum.
Figure 29 shows a 4-channel isolated interface connected to
ENCODE
DECODE
ENCODE
DECODE
ENCODE
DECODE
ENCODE
DECODE
VIA
VIB
VIC
VID
VOA
VOB
VOC
VOD
TO SCLK
TO SDIN
TO CS
TO LDAC
ADuM1400*
SERIAL CLOCK OUT
SERIAL DATA OUT
SYNC OUT
CONTROL OUT
MICROCONTROLLER
*ADDITIONAL PINS OMITTED FOR CLARITY.
06469-
027
Figure 29. Isolated Interface