AD5726(Rev0) Ver la hoja de datos (PDF) - Analog Devices
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AD5726 Datasheet PDF : 20 Pages
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APPLICATIONS
POWER-UP SEQUENCE
To prevent CMOS latch-up conditions, powering AVDD, AVSS,
and GND prior to any reference voltages is recommended. The
ideal power-up sequence is GND, AVSS, AVDD, VREFP, VREFN, and
the digital inputs. Noncompliance with the power-up sequence
over an extended period can elevate the reference currents and
eventually damage the device. On the other hand, if the non-
compliant power-up sequence condition is as short as a few
milliseconds, the device can resume normal operation without
damage once AVDD/AVSS are powered up.
REFERENCE CONFIGURATION
Output voltage ranges can be configured as either unipolar or
bipolar, and within these choices, a wide variety of options
exists. The unipolar configuration can be either a positive (as
shown in Figure 23) or a negative voltage output. The bipolar
configuration can be either symmetrical (as shown in Figure 24)
or nonsymmetrical.
+15V
+15V
+
INPUT
OUTPUT
OP1177
VREFP
0.2µF
ADR01
TRIM
10kΩ
VREFN
AVDD
AD5726
0.1µF║10µF
+10V OPERATION
AVSS
BALANCE
100kΩ
GAIN
100kΩ
–15V
Figure 23. Unipolar +10 V Operation
+15V
39kΩ
+15V
64
3
6.2Ω
12
1
0.2µF
AD688 FOR ±10V
AD588 FOR ±5V
5
14
AVDD
VREFP
AD5726
6.2Ω
15
0.2µF
8
13
7
VREFN
AVSS
1µF
–15V
±5 OR ±10V OPERATION
Figure 24. Symmetrical Bipolar Operation
0.1µF║10µF
AD5726
Figure 24 (symmetrical bipolar operation) shows the AD5726
configured for ±10 V operation. See the AD688 datasheet for a
full explanation of the reference operation.
Adjustments may not be necessary for many applications
because the AD688 is a very high accuracy reference. However,
if additional adjustments are required, adjust the AD5726 full-
scale first. Begin by loading the digital full-scale code (0xFFF).
Then, modify the gain adjust potentiometer to attain a DAC
output voltage of 9.9976 V. Next, alter the balance adjust to set
the midscale output voltage to 0.000 V.
The 0.2 μF bypass capacitors shown at their reference inputs in
Figure 24 should be used whenever ±10 V references are used.
Applications with single references or references to ±5 V may
not require the 0.2 μF bypassing. The 6.2 Ω resistor in series
with the output of the reference amplifier keeps the amplifier
from oscillating with the capacitive load. This has been found to
be large enough to stabilize this circuit. Larger resistor values
are acceptable if the drop across the resistor does not exceed a VBE.
Assuming a minimum VBE of 0.6 V and a maximum current of
2.75 mA, the resistor should be under 200 Ω for the loading of a
single AD5726.
Using two separate references is not recommended. Having two
references may cause different drifts with time and temperature,
whereas with a single reference, most drifts track.
Unipolar positive full-scale operation can usually be set by a
reference with the correct output voltage. This is preferable to
using a reference and dividing down to the required value. For a
10 V full-scale output, the circuit can be configured as shown in
Figure 25. In this configuration, the full-scale value is first set by
adjusting the 10 kΩ resistor for a full-scale output of 9.9976 V.
+15V
U1
0.1µF║10µF
+15V
AVDD
VREFP
AD5726
VREFN
AVSS
VIN
VOUT
ADR01
TEMP TRIM
GND
+15V
0.2µF
U2
V+
OP1177
V–
–15V 0V TO –10V OPERATION
–15V
Figure 25. Unipolar −10 V Operation
Figure 25 shows the AD5726 configured for −10 V to 0 V opera-
tion. An ADR01 and OP1177 are configured to produce a −10 V
output that is connected directly to VREFP for the reference voltage.
Rev. 0 | Page 15 of 20
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