AD5040/AD5060
Rev. A | Page 19 of 24
APPLICATIONS
CHOOSING A REFERENCE FOR THE AD5040/
AD5060
To achieve the optimum performance from the AD5040/
AD5060, carefully choose a precision voltage reference. The
AD5040/AD5060 have 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 to consider 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 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 an ADR43x
device, 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 temperature to trim
out any errors.
Because the supply current required by the AD5040/AD5060 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.
SYNC
SCLK
DIN
7V
5V
V
OUT
= 0V TO 5V
ADR395
04767-036
3-WIRE
SERIAL
INTERFACE
AD5040/
AD5060
Figure 50. ADR395 as Reference to AD5060/AD5040
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
output voltage affects INL, DNL, and TUE. A reference with a
tight temperature coefficient specification should be chosen to
reduce the 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 8 shows
examples of recommended precision references for use as a
supply to the AD5040/AD5060.
Table 8. Precision References for the AD5040/AD5060
Part No.
Initial
Accuracy
(mV max)
Temp. 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 AD5040/
AD5060
The AD5040/AD5060 have been designed for single-supply
operation, but a bipolar output range is also possible using the
circuit in Figure 51. 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
⎥
⎦
⎤
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
×−
⎟
⎠
⎞
⎜
⎝
⎛
+
×
⎟
⎠
⎞
⎜
⎝
⎛
×=
1R
2R
V
1R
2R1RD
VV
DDDD
O
65536
where D represents the input code in decimal (0 to 65536,
AD5060).
With V
REF
= 5 V, R1 = R2 = 10 kΩ:
V5
65536
10
−
⎟
⎠
⎞
⎜
⎝
⎛
×
=
D
V
O
Using the AD5060, 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 .
+5V
10μF
04767-037
R1 = 10kΩ
V
OUT
V
REF
0.1μF
3-WIRE
SERIAL
INTERFACE
AD820/
OP295
+
–
–5V
+5V
R2 = 10k
±5V
AD5040/
AD5060
Figure 51. Bipolar Operation with the AD5040/AD5060
