Datasheet

ADR440/ADR441/ADR443/ADR444/ADR445
Rev. E | Page 15 of 20
APPLICATIONS INFORMATION
OUTPUT ADJUSTMENT
The ADR44x family features a TRIM pin that allows the user to
adjust the output voltage of the part over a limited range. This
allows errors from the reference and overall system errors to be
trimmed out by connecting a potentiometer between the output
and the ground, with the wiper connected to the TRIM pin.
Figure 35 shows the optimal trim configuration. R1 allows fine
adjustment of the output and is not always required. R
P
should
be sufficiently large so that the maximum output current from
the ADR44x is not exceeded.
TRIM
V
IN
V
O
= ±0.5%
0.1µF
0.1µF
GND
R2
1kΩ
R
P
10kΩ
05428-035
V
OUT
6
2
5
4
R1
100kΩ
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
Figure 35. ADR44x Trim Function
Using the trim function has a negligible effect on the temperature
performance of the ADR44x. However, all resistors need to be
low temperature coefficient resistors, or errors may occur.
BIPOLAR OUTPUTS
By connecting the output of the ADR44x to the inverting ter-
minal of an operational amplifier, it is possible to obtain both
positive and negative reference voltages. Care must be taken
when choosing Resistors R1 and R2 (see Figure 36). These
resistors must be matched as closely as possible to ensure mini-
mal differences between the negative and positive outputs. In
addition, care must be taken to ensure performance over
temperature. Use low temperature coefficient resistors if the
circuit is used over temperature; otherwise, differences exist
between the two outputs.
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
6
2
4
V
IN
V
OUT
GND
R1
10kΩ
R2
10kΩ
R3
5kΩ
–10V
+10V
–5V
+5V
0.1µF
0.1µF
05428-036
+
V
DD
Figure 36. ADR44x Bipolar Outputs
PROGRAMMABLE VOLTAGE SOURCE
To obtain different voltages than those offered by the ADR44x,
some extra components are needed. In Figure 37, two potenti-
ometers are used to set the desired voltage and the buffering
amplifier provides current drive. The potentiometer connected
between V
OUT
and GND, with its wiper connected to the
noninverting input of the operational amplifier, takes care of
coarse trim. The second potentiometer, with its wiper connected
to the trim terminal of the ADR44x, is used for fine adjustment.
Resolution depends on the end-to-end resistance value and the
resolution of the selected potentiometer.
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
6
2
4
V
IN
V
OUT
GND
R2
10kΩ
ADJ V
REF
05428-038
+
V
DD
R1
10kΩ
Figure 37. Programmable Voltage Source
For a completely programmable solution, replace the two
potentiometers in Figure 37 with one Analog Devices dual
digital potentiometer, offered with either an SPI or an I
2
C
interface. These interfaces set the position of the wiper on both
potentiometers and allow the output voltage to be set. Table 9
lists compatible Analog Devices digital potentiometers.