AD5320
Rev. C | Page 15 of 20
APPLICATIONS
USING REF19X AS A POWER SUPPLY FOR AD5320
Because the supply current required by the AD5320 is
extremely low, an alternative option is to use a REF19x voltage
reference (REF195 for 5 V or REF193 for 3 V) to supply the
required voltage to the part (see
Figure 32). This is especially
useful if the power supply is noisy or if the system supply
voltages are at some value other than 5 V or 3 V (such as 15 V).
The REF19x outputs a steady supply voltage for the AD5320. If
the low dropout REF195 is used, the current it needs to supply
to the AD5320 is 140 μA. This is with no load on the output of
the DAC. When the DAC output is loaded, the REF195 also
needs to supply the current to the load. The total current
required (with a 5 kΩ load on the DAC output) is:
140 μA + (5 V/5 kΩ) = 1.14 mA
The load regulation of the REF195 is typically 2 ppm/mA,
which results in an error of 2.3 ppm (11.5 μV) for the 1.14 mA
current drawn from it. This corresponds to a 0.009 LSB error.
REF195
AD5320
DIN
SCLK
SYNC
15
5V
140µA
V
OUT
= 0V TO 5V
3-WIRE
SERIAL
INTERFACE
00934-032
Figure 32. REF195 as Power Supply to AD5320
BIPOLAR OPERATION USING THE AD5320
The AD5320 is designed for single-supply operation but a bipolar
output range is also possible using the circuit in
Figure 33. The
circuit below gives an output voltage range of ±5 V. Rail-to-rail
operation at the amplifier output is achievable using an AD820 or
an OP295 as the output amplifier.
The output voltage for any input code can be calculated as
follows:
⎥
⎦
⎤
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
×−
⎟
⎠
⎞
⎜
⎝
⎛
+
×
⎟
⎠
⎞
⎜
⎝
⎛
×=
1
2
1
21
4096 R
R
V
R
RR
D
VV
DDDD
O
where
D represents the input code in decimal (0 to 4095).
With
V
DD
= 5 V, R1 = R2 = 10 kΩ:
V
D
V
O
5
4096
10
−
⎟
⎠
⎞
⎜
⎝
⎛
×
=
This is an output voltage range of ±5 V with 000 hex
corresponding to a −5 V output and FFF hex corresponding to
a +5 V output.
3-WIRE SERIAL INTERFACE
+5V
AD5320
10µF
0.1µF
V
DD
V
OUT
R1 = 10kΩ
R2 = 10k
+5V
±5
–5V
AD820/
OP295
00934-033
Figure 33. Bipolar Operation with the AD5320
USING AD5320 WITH AN OPTO-ISOLATED
INTERFACE
For 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 can occur in the area where the DAC is
functioning. Opto-isolators provide isolation in excess of 3 kV.
Because the AD5320 uses a 3-wire serial logic interface, it
requires only three opto-isolators to provide the required
isolation (see
Figure 34). The power supply to the part also
needs to be isolated. This 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 AD5320.
V
DD
0.1µF
V
DD
10kΩ
10kΩ
V
DD
10kΩ
5V
REGULATOR
V
OUT
GND
DIN
SYNC
SCLK
POWER
10µF
V
DD
SYNC
SCLK
DATA
AD5320
00934-034
Figure 34. AD5320 with An Opto-Isolated Interface
