Datasheet

AD5310 Data Sheet
Rev. B | Page 14 of 16
APPLICATIONS INFORMATION
USING REF19x AS A POWER SUPPLY FOR AD5310
Because the supply current required by the AD5310 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 quite noisy or if the system supply voltages are at some
value other than 5 V or 3 V (for example, 15 V). The REF19x
outputs a steady supply voltage for the AD5310. If the low dropout
REF195 is used, the current that it needs to supply to the AD5310
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 0.002 LSB error.
Figure 32. REF195 as Power Supply to AD5310
BIPOLAR OPERATION USING THE AD5310
The AD5310 is designed for single-supply operation but a bipolar
output range is also possible using the circuit shown in Figure 33.
This circuit results in 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:












×−






+
×






×=
R1
R2
V
R1
R2R1D
VV
DDDD
O
1024
where D represents the input code in decimal (0 to 1023).
With V
DD
= 5 V, R1 = R2 = 10 kΩ,
V5
1024
10
−






×
=
D
V
O
This is an output voltage range of ±5 V, with 000 hex corresponding
to a −5 V output and 3FF hex corresponding to a +5 V output.
Figure 33. Bipolar Operation with the AD5310
USING AD5310 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 AD5310 uses a 3-wire serial logic interface, it only
requires 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 AD5310.
Figure 34. AD5310 with an Opto-Isolated Interface