AD5062
Rev. A | Page 17 of 20
APPLICATIONS
CHOOSING A REFERENCE FOR THE AD5062
To achieve the optimum performance from the AD5062,
thought should be given to the choice of a precision voltage
reference. The AD5062 has just one reference input, VREF. The
voltage on the reference input is used to supply the positive
input to the DAC. Therefore, any error in the reference is
reflected in the DAC.
There are four possible sources of error when choosing a
voltage reference for high accuracy applications: initial
accuracy, ppm drift, long-term drift, and output voltage noise.
Initial accuracy on the output voltage of the DAC will lead to a
full-scale error in the DAC. To minimize these errors, a refer-
ence with high initial accuracy is preferred. Also, choosing a
reference with an output trim adjustment, such as the ADR43x
family, allows a system designer to trim out system errors by
setting a reference voltage to a voltage other than the nominal.
The trim adjustment can also be used at the operating
temperature to trim out any error.
Because the supply current required by the AD5062 is
extremely low, the parts are ideal for low supply applications.
The ADR395 voltage reference is recommended. This requires
less than 100 μA of quiescent current and can, therefore, drive
multiple DACs in one system, if required. It also provides very
good noise performance at 8 μV p-p in the 0.1 Hz to 10 Hz range.
04766-036
AD5062
SYNC
SCLK
DIN
7V
5V
VOUT = 0V TO 5V
ADR395
3-WIRE
SERIAL
INTERFACE
Figure 42. ADR395 as Reference to AD5062
Long-term drift is a measure of how much the reference drifts
over time. A reference with a tight long-term drift specification
ensures that the overall solution remains relatively stable during
its entire lifetime. The temperature coefficient of a reference’s
output voltage affects INL, DNL, and TUE. A reference with a
tight temperature coefficient specification should be chosen to
reduce temperature dependence of the DAC output voltage on
ambient conditions.
In high accuracy applications, which have a relatively low noise
budget, reference output voltage noise needs to be considered. It
is important to choose a reference with as low an output noise
voltage as practical for the system noise resolution required.
Precision voltage references, such as the ADR435, produce low
output noise in the 0.1 Hz to 10 Hz region.
Table 7 shows
examples of recommended precision references for use as
supply to the AD5062.
Table 7. Precision References Part List for the AD5062
Part
No.
Initial
Accuracy
(mV max)
Temperature
Drift
(ppm/°C max)
0.1 Hz to 10 Hz
Noise (μV p-p typ)
ADR435
±2
3 (SO-8)
8
ADR425
±2
3 (SO-8)
3.4
ADR02
±3
3 (SO-8)
10
ADR02
±3
3 (SC70)
10
ADR395
±5
9 (TSOT-23)
8
BIPOLAR OPERATION USING THE AD5062
The AD5062 has been designed for single-supply operation, but
a bipolar output range is also possible using the circuit in
Figure 43. The circuit shown yields an output voltage range of
±5 V. Rail-to-rail operation at the amplifier output is achievable
using an AD820/AD8032 or an OP196/OP295.
The output voltage for any input code can be calculated as
follows:
×
+
×
×
=
1
R
2
R
V
1
R
2
R
1
R
D
V
DD
O
65536
where D represents the input code in decimal (0–65536).
With VREF = 5 V, R1 = R2 = 10 kΩ:
V
5
65536
10
×
=
D
V
O
This is an output voltage range of ±5 V with 0x0000
corresponding to a 5 V output and 0xFFFF corresponding to a
+5 V output.
AD5062
+5V
10F
04
766
-03
7
R1 = 10k
VOUT
VREF
0.1F
3-WIRE
SERIAL
INTERFACE
AD820/
OP295
+
–
–5V
+5V
R2 = 10k
±5V
Figure 43. Bipolar Operation with the AD5062