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AN-1208
APPLICATION NOTE
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Programmable Bidirectional Current Source Using the AD5292 Digital
Potentiometer and the ADA4091-4 Op Amp
Rev. C | Page 1 of 3
CIRCUIT FUNCTION AND BENEFITS
The circuit in Figure 1 provides a programmable bidirectional
Howland current source using the AD5292 digital potentiometer
in conjunction with the quad ADA4091-4 op amp and the
ADR512 voltage reference. This circuit offers 10-bit resolution
over an output current range of ±18.4 mA. The AD5292 is
programmable over an SPI-compatible serial interface.
The ±1% resistor tolerance of the AD5292 allows it to be placed
in series with external divider resistors, as shown in Figure 5, to
reduce the maximum output current without the need to match
the resistors in the circuit. Reducing the I
OUT
range serves to
increase the sensitivity of the output current.
The AD5292 has an internal 20-times programmable memory
that allows a customized I
OUT
at power-up. The circuit provides
accurate, low noise, and low tempco output voltage capability
and is well suited for digital calibration applications.
CIRCUIT DESCRIPTION
Table 1. Devices Connected/Referenced
Product Description
AD5292
Digital potentiometer, 10 bits, 1% resistor
tolerance
ADA4091-4
Micropower, overvoltage protected (OVP),
rail-to-rail op amp
ADR512 Low noise, precision 1.2 V reference
This circuit employs the AD5292 digital potentiometer in
conjunction with the ADR512 reference and the ADA4091-4 op
amp, providing a 10-bit, programmable, bidirectional current
source. The circuit guarantees monotonicity, ±1 LSB DNL, and
has an integral nonlinearity of ±2 LSB, typical.
The bipolar high voltage regulator consists of a low voltage
reference followed by a noninverting and an inverting amplifier
whose gains are set by the ratio of R
1
to R
2
.and R
3
to R
4
. The
ADR512 1.200 V voltage reference has low temperature drift,
high accuracy, and ultralow noise performance.
–15V
–13.8V
–15V
–V
08459-001
AD5292
ADR512
+V
V
SS
V
W
V
DD
V
1
R
1
R
2
3.9kΩ
10nF
10pF
R
BIAS
U1B
U1C
U1A
R
AB
20kΩ
+15V
+13.8V
+15V
V
DD
–V
2
+15V
+1.2V
10.5kΩ ± 1%
1kΩ ± 1%
R
9
R
3
1kΩ
SERIAL
INTERFACE
ADA4091-4
3/4
ADA4091-4
3/4
ADA4091-4
1/4
ADA4091-4
2/4
1kΩ ± 1%
R
4
11.5kΩ ± 1%
R
6
16.5kΩ ± 1%
C
1
10pF
C
2
R
6A
R
LOAD
I
OUT
1.05kΩ ± 1%
R
6B
50Ω ± 1%
R
8
1.1kΩ ± 1%
U1D
R
7
16.5kΩ ± 1%
Figure 1. Programmable Bidirectional Current Source (Simplified Schematic: Decoupling and All Connections Not Shown)
