Datasheet

Data Sheet AD5725
Rev. C | Page 17 of 20
POWER SUPPLIES
Power supplies required are AV
SS
, AV
DD
, and V
L
. The AV
SS
supply can be set between −15 V and 0 V. AV
DD
is the positive
supply; its operating range is between +5 V and +15 V.
V
L
is the digital output supply voltage for the readback function.
It is normally connected to +5 V. This pin is a logic reference
input only. It does not supply current to the device. If the readback
function is not used, V
L
can be left open-circuit. While V
L
does
not supply current to the AD5725, it does supply current to the
digital outputs when the readback function is used.
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 or a
negative voltage output, and the bipolar configuration can be
either symmetrical or nonsymmetrical.
06442-007
ADR01
+15V
INPUT
OUTPUT
TRIM
10kΩ
+10V OPERATION
+15V
AD5725
–15V
OP1177
AV
DD
AV
SS
V
REFP
0.2µF
V
REFN
+
10µF
0.1µF
10µF
0.1µF
Figure 27. Unipolar +10 V Operation
0.2µF
AD5725
+15V
+15V
–15V
AV
DD
V
REFP
V
REFN
AV
SS
BALANCE
100kΩ
GAIN
100kΩ
46
12
5
138
3
1
14
15
7
6.2Ω
0.2µF
6.2Ω
1µF
39kΩ
AD688 FOR ±10V
AD588 FOR ±5V
06442-008
±5 OR ±10V OPERATION
10µF
0.1µF
10µF
0.1µF
Figure 28. Symmetrical Bipolar Operation
Figure 28 (Symmetrical Bipolar Operation) shows the AD5725
configured for ±10 V operation. See the AD688 data sheet for a
full explanation of reference operation. Adjustments may not be
required for many applications since the AD688 is a very high
accuracy reference. However, if additional adjustments are
required, adjust the AD5725 full scale first. Begin by loading the
digital full-scale code (0xFFF). Then, adjust the gain adjust
potentiometer to attain a DAC output voltage of 9.9976 V.
Then, adjust the balance adjust to set the mid-scale output
voltage to 0.000 V.
The 0.2 µF bypass capacitors shown at the reference inputs in
Figure 28 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 is to keep the amplifier
from oscillating with the capacitive load. We have found that
this is large enough to stabilize this circuit. Larger resistor
values are acceptable, provided that the drop across the resistor
does not exceed a V
BE
. Assuming a minimum V
BE
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 AD5725.
Using two separate references is not recommended. Having two
references can cause different drifts with time and temperature,
whereas with a single reference, most drifts will track.
Unipolar positive full-scale operation can usually be set with 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 29. In this configuration, the full-scale value is set first by
adjusting the 10 kΩ resistor for a full-scale output of 9.9976 V.