Datasheet AD202, AD204 (Analog Devices) - 9

AD202/AD204 CHANNEL 0 CHANNEL 1
Figure 17. A three-pole active filter is included in the design to
HI LO HI LO
get normal-mode rejection of frequencies above a few Hz and to provide enhanced common-mode rejection at 60 Hz. If offset adjustment is needed, it is best done at the trim pins of the OP07 itself; gain adjustment can be done at the feedback resistor. Note that the isolated supply current is large enough to mandate the use of 1 mF supply bypass capacitors. This circuit can be
RF RG RF RG
used with an AD202 if a low power op amp is used instead of
0.1”
the OP07.
GRID Process Current Input with Offset.
Figure 18 shows an isolator receiver that translates a 4-20 mA process current
100pF 100pF
signal into a 0 V to 10 V output. A 1 V to 5 V signal appears at the isolator’s output, and a –1 V reference applied to output LO provides the necessary level shift (in multichannel applications,
1 1
the reference can be shared by all channels). This technique is
2 2 3 3
often useful for getting offset with a follower-type output buffer.
4 4 5 5 6 6 AD202 OR AD204 +15V + 1V + TO 4–20mA 250 5V – 15k 0V –15V TO
Figure 16b.
10V –1V TO 1k 10k Synchronization.
Since AD204s operate from a common
ADDITIONAL – CHANNELS
clock, synchronization is inherent. AD202s will normally not
237 AD589
interact to produce beat frequencies even when mounted on
6.8k
0.25-inch centers. Interaction may occur in rare situations where a large number of long, unshielded input cables are bundled
–15V
together and channel gains are high. In such cases, shielded cable may be required or AD204s can be used. Figure 18. Process Current Input Isolator with Offset The circuit as shown requires a source compliance of at least
APPLICATIONS EXAMPLES
5 V, but if necessary that can be reduced by using a lower value
Low Level Sensor Inputs.
In applications where the output of of current-sampling resistor and configuring the input amplifier low level sensors such as thermocouples must be isolated, a low for a small gain. drift input amplifier can be used with an AD204, as shown in
0.15 F AD204 39k HI + 470k 470k + AD OP-07 50k 1 F VO = VI 1 +
( )
0.038 R F G 49.9k – RG LO + 1 F 1 F CLK 220M + +7.5V OPTIONAL OPEN INPUT –7.5V CLK RET DETECTION
Figure 17. Input Amplifier and Filter for Sensor Signals (NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to Page 3 for proper DIP package pinout.) REV. D –9– Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION PRODUCT HIGHLIGHTS SPECIFICATIONS AD246–SPECIFICATIONS AD246 Pin Designations PIN DESIGNATIONS ORDERING GUIDE DIFFERENCES BETWEEN THE AD202 AND AD204 INSIDE THE AD202 AND AD204 USING THE AD202 AND AD204 Powering the AD204 AD246 Clock Drive Input Configurations Adjustments Common-Mode Performance Dynamics and Noise Using Isolated Power Operation at Reduced Signal Swing PCB Layout for Multichannel Applications Synchronization APPLICATIONS EXAMPLES Low Level Sensor Inputs Process Current Input with Offset High Compliance Current Source Motor Control Isolator. Floating Current Source/Ohmmeter Photodiode Amplifier OUTLINE DIMENSIONS Revision History