Datasheet

AD5061
Rev. B | Page 18 of 20
APPLICATIONS
CHOOSING A REFERENCE
To achieve the optimum performance from the AD5061,
thought should be given to the choice of a precision voltage
reference. The AD5061 has just one reference input, V
REF
. 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 vol-
tage 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 leads to a full-scale
error in the DAC. To minimize these errors, a reference 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 errors.
Because the supply current required by the AD5061 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.
AD5061
SYNC
SCLK
DIN
7V
5V
V
OUT
= 0V TO 5V
ADR395
04762-036
3-WIRE
SERIAL
INTERFACE
Figure 46. ADR395 as Reference to the AD5061
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 a supply to the AD5061.
Table 7. Precision References Part List for the AD5061
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
The AD5061 has been designed for single-supply operation, but
a bipolar output range is also possible using the circuit shown in
Figure 47. The circuit shown yields an output voltage range of
±5 V. Rail-to-rail operation at the amplifier output is achievable
using an AD8675/AD820/AD8032 or an OP196/OP295.
The output voltage for any input code can be calculated as
follows:
⎥
⎦
⎤
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
×−
⎟
⎠
⎞
⎜
⎝
⎛
+
×
⎟
⎠
⎞
⎜
⎝
⎛
×=
1R
2R
V
1R
2R1RD
VV
DDDD
O
65536
where D represents the input code in decimal (0 to 65536).
With V
REF
= 5 V, R1 = R2 = 10 kΩ,
V5
65536
10
−
⎟
⎠
⎞
⎜
⎝
⎛
×
=
D
V
O
This is an output voltage range of ±5 V with 0x0000 correspond-
ing to a −5 V output and 0xFFFF corresponding to a +5 V output.
AD5061
+5V
10µF
04762-037
R1 = 10kΩ
V
BF
V
OUT
V
REF
0.1µF
3-WIRE
SERIAL
INTERFACE
AD820/
OP295
+
–
–5V
+5V
R2 = 10k
Ω
±5V
Figure 47. Bipolar Operation with the AD5061