AD5726 Analog Devices, AD5726 Datasheet - Page 16

• Manufacturer Part Number: AD5726
• Description: Quad, 12-Bit, Serial Input, Unipolar/Bipolar, Voltage Output DAC
• Manufacturer: Analog Devices

Specifications of AD5726

• Resolution (bits): 12bit
• Dac Update Rate: 111kSPS
• Dac Settling Time: 9µs
• Max Pos Supply (v): +15.75V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

AD5726
Single 5 V Supply Operation
For operation with a 5 V supply, the reference voltage should
be set between 1.0 V and 2.5 V for optimum linearity. Figure 28
shows an
headroom of the reference and DAC are both sufficient to support
a +5 V supply with ±5 V tolerance.
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. The 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.
AD780
5V
INPUT
GND
AD780
0V TO 2.5V OPERATION
SINGLE 5V SUPPLY
OUTPUT
TRIM
10µF
Figure 28. 5 V Single-Supply Operation
used to supply a 2.5 V reference voltage. The
10kΩ
0.01µF
0.2µF
V
V
REFP
REFN
*ADDITIONAL PINS OMITTED FOR CLARITY.
MICROCONTROLLER
SERIAL CLOCK OUT
SERIAL DATA OUT
AD5726
AV
AV
CONTROL OUT
DD
SS
SYNC OUT
0.1µF║10µF
V
V
V
V
IB
IA
IC
ID
Figure 29. Isolated Interface
Rev. B | Page 16 of 20
ENCODE
ENCODE
ENCODE
ENCODE
ADuM1400*
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, typically in 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.
The AD5726 should have ample supply bypassing located as
close to the package as possible. Recommended capacitor values
are 10 μF in parallel with 0.1 μF. The 0.1 μF 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 from any
hazardous common-mode voltages that may occur. Isocouplers
provide voltage isolation in excess of 2.5 kV. The serial loading
structure of the 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
the AD5726 using an ADuM1400.
DECODE
DECODE
DECODE
DECODE
V
V
V
V
OA
OB
OC
OD
TO SCLK
TO SDIN
TO CS
TO LDAC