AN-968
APPLICATION NOTE
One Technology Way • P. O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Te l: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
Current Sources: Options and Circuits
by Martin Murnane
Rev. 0 | Page 1 of 4
DOUT/RDY
DIN
SCLK
CS
DV
DD
SERIAL
INTERFACE
AND
LOGIC
CONTROL
-
ADC
AD7794/AD7795
AIN1(+)
REFIN1(+)
AIN1(–)
AIN2(+)
AIN2(–)
AIN3(+)
AIN3(–)
REFIN2(+)
IOUT1
REFIN1(–)
IN-AMP
V
DD
GND
MUX
PSW
GND
INTERNAL
CLOCK
CLK
GND AV
DD
V
DD
IN+
IN–
OUT– OUT+
IN+
IN–
OUT– OUT+
R
CM
V
DD
REFIN2(–)
BUF
07488-001
Figure 1. AD7794 Current Source Application (See AD7794 Data Sheet for More Details)
INTRODUCTION
Many applications require current sources to excite various devices
for sensor drive, accurate measurement, and other applications.
This application note discusses several options that are available
to designers when designing current sources using ICs from
Analog Devices, Inc. It shows examples of current sources from
the microampere range which are integrated in specific devices
and also medium to high power discrete applications up to the
1 A range.
LOW CURRENT—ADC APPLICATION
Some ADCs are designed specifically for direct sensor
attachment with internal constant current sources, also
called excitation currents.
The AD7794 device has two programmable excitation currents
that can be programmed from 10 μA to 1 mA (see Figure 1).
The current sources are controlled via a register (I/O register)
that enables and directs the current to one of two output pins,
in this case IOUT1 (see Figure 1 for details). This is adequate
for low power portable applications where sensor power
consumption must be low.
