AD5663 Analog Devices, AD5663 Datasheet - Page 19

• Manufacturer Part Number: AD5663
• Manufacturer: Analog Devices

Specifications of AD5663

• Resolution (bits): 16bit
• Dac Update Rate: 220kSPS
• Dac Settling Time: 4µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

APPLICATIONS
CHOOSING A REFERENCE FOR THE AD5663
To achieve the optimum performance from the AD5663,
thought should be given to the choice of a precision voltage
reference. The AD5663 has only one reference input, V
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.
When choosing a voltage reference for high accuracy applica-
tions, the sources of error are 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 ADR423, allows a system designer
to trim system errors out 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 error.
Long-term drift is a measurement of how much the reference
drifts over time. A reference with a tight long-term drift specifi-
cation 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 in 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 ADR425, produce low
output noise in the 0.1 Hz to 10 Hz range. Examples of recom-
mended precision references for use as supplies to the AD5663
are shown in the Table 15.
Table 15. Partial List of Precision References for Use with the AD5663
Part No.
ADR425
ADR395
REF195
AD780
ADR423
Initial Accuracy (mV Max)
±2
±6
±2
±2
±2
Temperature Drift (ppm
3
25
5
3
3
REF
.
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USING A REFERENCE AS A POWER SUPPLY FOR
THE AD5663
Because the supply current required by the AD5663 is extremely
low, an alternative option is to use a voltage reference to supply
the required voltage to the part (see Figure 36). 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 voltage reference outputs a steady supply voltage for
the AD5663; see Table 15 for a suitable reference. If the low drop-
out
AD5663, 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
The load regulation of the REF195 is typically 2 ppm/mA,
which results in a 2.5 ppm (12.5 μV) error for the 1.25 mA
current drawn from it. This corresponds to a 0.164 LSB error.
o
C Max)
REF195
THREE-WIRE
250 μA + (5 V/5 kΩ) = 1.25 mA
INTERFACE
SERIAL
Figure 36. REF195 as Power Supply to the AD5663
is used, it must supply 250 μA of current to the
0.1 Hz to 10 Hz Noise (μV p-p Typ)
3.4
5
50
4
3.4
SYNC
SCLK
DIN
15V
REF195
5V
V
AD5663
DD
V
REF
500µA
V
OUT
= 0V TO 5V
AD5663
V
5
5
5
2.5/3
3
OUT
(V)