
AD5300
–11–
REV. 0
R2 = 10k
V
+5V
–5V
AD820/
OP295
3-WIRE
SERIAL
INTERFACE
+5V
AD5300
10
m
F
0.1
m
F
V
DD
V
OUT
R1 = 10k
V
6
5V
Figure 30. Bipolar Operation with the AD5300
T wo 8-Bit AD5300s T ogether Make One 15-Bit DAC
By using the configuration below in Figure 31, it can be seen
that one 15-bit DAC can be made with two 8-bit AD5300s.
Because of the low supply current the AD5300 requires, the
output of one DAC may be directed into the supply pin of the
second DAC. T he first DAC has no problem sourcing the re-
quired 140
μ
A of current for the second DAC.
Since the AD5300 works on any supply voltage between 2.5 V
and 5.5 V, the output of the first DAC can be anywhere above
2.5 V. For a V
DD
of 5 V this allows the first DAC to use half of
its output range (2.5 V to 5 V), which gives 7-bit resolution on
the output voltage. T his output then becomes the supply and
reference for the second DAC. T he second DAC has 8-bit reso-
lution on the output range, which gives an overall resolution for
the system of 15 bits.
A level-shifter is required to ensure that the logic input voltages
do not exceed the supply voltage of the part. T he microcontroller
outputs 5 V signals which need to be level-shifted down to 2.5 V
in the case of the second DAC having a supply of only 2.5 V.
AD5300
V
DD
SYNC
SCLK
DIN
+5V
MICRO-
CONTROLLER
V
OUT
= 2.5 TO 5V
LEVEL
SHIFTER
V
OUT
= 0 TO 5V
15-BIT RESOLUTION
SYNC
SCLK
DIN
V
DD
AD5300
Figure 31. 15-Bit DAC Using Two AD5300s
Using AD5300 with an Opto-Isolated Interface
In process-control applications in industrial environments it is
often necessary to use an opto-isolated interface to protect and
isolate the controlling circuitry from any hazardous common-
mode voltages that may occur in the area where the DAC is
functioning. Opto-isolators provide isolation in excess of 3 kV.
Because the AD5300 uses a three-wire serial logic interface, it
requires only three opto-isolators to provide the required isola-
tion (see Figure 32). T he power supply to the part also needs to
be isolated. T his 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 AD5300.
V
DD
0.1
m
F
V
DD
10k
V
10k
V
V
DD
10k
V
+5V
REGULATOR
V
OUT
GND
DIN
SYNC
SCLK
POWER
10
m
F
V
DD
SYNC
SCLK
DATA
AD5300
Figure 32. AD5300 with an Opto-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. T he printed circuit board containing the AD5300 should
have separate analog and digital sections, each having its own
area of the board. If the AD5300 is in a system where other
devices require an AGND to DGND connection, the connec-
tion should be made at one point only. T his ground point should
be as close as possible to the AD5300.
T he power supply to the AD5300 should be bypassed with
10
μ
F and 0.1
μ
F capacitors. T he capacitors should be physi-
cally as close as possible to the device with the 0.1
μ
F capacitor
ideally right up against the device. T he 10
μ
F capacitors are the
tantalum bead type. It is important that the 0.1
μ
F capacitor has
low Effective Series Resistance (ESR) and Effective Series In-
ductance (ESI), e.g. common ceramic types of capacitors. T his
0.1
μ
F capacitor provides a low impedance path to ground for
high frequencies caused by transient currents due to internal
logic switching.
T he power supply line itself should have as large a trace as pos-
sible 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 through the board. T he 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 two-layer board.