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Circuit Note
CN-0151
Circuit Designs Using Analog Devices Products
Apply these product pairings quickly and with confidence.
For more information and/or support call 1-800-AnalogD
(1-800-262-5643) or visit www.analog.com/circuit.
Devices Connected/Referenced
AD5446/
AD5543
14-/16-Bit High Bandwidth DACs
with Serial Interface
OP1177/
AD8510
Precision, Low Noise, Low Input Bias
Current Op Amps
ADR425/
ADR512
Precision, Low Noise 5 V/1.2 V References
Versatile High Precision Programmable Current Sources Using DACs,
Op Amps, and MOSFET Transistors
Rev. A
“Circuits from the Lab” from Analog Devices have been designed and built by Analog Devices
engineers. Standard engineering practices have been employed in the design and construction of
each circuit, and their function and performance have been tested and verified in a lab environment
at room temperature. However, you are solely responsible for testing the circuit and determining its
suitability and applicability for your use and application. Accordingly, in no event shall Analog
Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to
any cause whatsoever connected to the use of any “Circuit from the Lab”. (Continued on last page)
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Tel: 781.329.4700
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Fax: 781.461.3113 ©2010-2011 Analog Devices, Inc. All rights reserved.
CIRCUIT FUNCTION AND BENEFITS
Digitally controlled current sources are critical functions in a
variety of applications, such as power management, solenoid
control, motor control, impedance measurement, sensor
excitation, and pulse oximetry. Here we describe three current
sources with serial interface digital control using DACs,
op amps, and MOSFET transistors.
The DACs selected are high resolution (14- or 16-bit), low
power CMOS with standard serial interfaces. The AD5543
16-bit DAC is packaged in ultracompact (3 mm × 4.7 mm)
8-lead MSOP and 8-lead SOIC packages. The AD5446 14-bit
DAC is available in a small 10-lead MSOP package. The two
DACs are both compatible with most DSP interface standards
and also SPI, QSPI, and MICROWIRE. The external reference
voltage input allows many output level variations, up to 10 V.
The combination of parts represents industry-leading small PC
board area, low cost, and high resolution. The three designs
offer low risk solutions and use industry-standard parts.
CIRCUIT DESCRIPTION
All three circuits require a single 5 V supply for the DACs and
±15 V supplies for the op amps. Some circuits may need an
accurate external voltage reference (see MT-087 Tutorial).
Each circuit contains two stages. The first stage is the input
stage, composed of the DAC and an op amp. The second stage is
an N-channel MOSFET transistor output stage (Figure 1 and
Figure 2), which supplies the current in response to the digital
word sent to the system.
The input stage of the circuit, shown in Figure 1, is composed of
a current output DAC (AD5446) and its op amp (AD8510). It
provides the conversion of the command word and drives the
transistor. It also modulates the voltage applied to the single
resistor. The command word is sent via an SPI interface.
The output stage is composed of an N-channel MOSFET
transistor (NTE4153N), which can provide more current
than the output of the op amp and a single resistor. The single
resistor, R1, produces the current with the voltage applied to its
pins. The transistor regulates this current.
4
5
6
7
8
9
10
1
2
3
2
3
4
7
6
3pF
+5V
+15V
−15V
+
−
D
S
G
R1
100Ω
NTE4153NT1G
I
LOAD
OUT
AD5446
SCLK
SDIN
SYNC
R
FB
V
DD
V
REF
I
OUT
1
I
OUT
2
GND
V
IN
SEE TEXT
SCLK
DIN
SDO
AGND
AGND
SDO
SYNC
AD8510
08977-001
Figure 1.
Current Source Using a Current Output DAC (All Connections and Decoupling Not Shown)
