AD202J View Datasheet(PDF) - Analog Devices

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Description

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AD202J

Low Cost, Miniature Isolation Amplifiers

Analog Devices 

AD202/AD204

CHANNEL 0 CHANNEL 1

HI LO

HI LO

0.1”

GRID

RF

RG RF

RG

100pF

100pF

1

1

2

2

3

3

4

4

5

5

6

6

Figure 16b.

Synchronization. Since AD204s operate from a common

clock, synchronization is inherent. AD202s will normally not

interact to produce beat frequencies even when mounted on

0.25-inch centers. Interaction may occur in rare situations where

a large number of long, unshielded input cables are bundled

together and channel gains are high. In such cases, shielded

cable may be required or AD204s can be used.

APPLICATIONS EXAMPLES

Low Level Sensor Inputs. In applications where the output of

low level sensors such as thermocouples must be isolated, a low

drift input amplifier can be used with an AD204, as shown in

Figure 17. A three-pole active filter is included in the design to

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

used with an AD202 if a low power op amp is used instead of

the OP07.

Process Current Input with Offset. Figure 18 shows an

isolator receiver that translates a 4-20 mA process current

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,

the reference can be shared by all channels). This technique is

often useful for getting offset with a follower-type output buffer.

AD202

OR

AD204

+15V

4–20mA

250⍀

+

1V

TO

5V

–

+

15k⍀

0V

–15V

TO

10V

–1V TO

ADDITIONAL

CHANNELS

237⍀

1k⍀

AD589

10k⍀

–

6.8k⍀

–15V

Figure 18. Process Current Input Isolator with Offset

The circuit as shown requires a source compliance of at least

5 V, but if necessary that can be reduced by using a lower value

of current-sampling resistor and configuring the input amplifier

for a small gain.

0.15␮F

39k⍀

HI

+

AD OP-07

470k⍀ 470k⍀

1␮F

49.9k⍀

0.038␮F

LO

220M⍀

OPTIONAL

OPEN INPUT

DETECTION

RG

+

1␮F

1␮F +

AD204

+

( ) VO = VI ؋

1

+

50k⍀

RG

–

+7.5V

–7.5V

CLK

CLK RET

Figure 17. Input Amplifier and Filter for Sensor Signals

REV. D

(NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to

Page 3 for proper DIP package pinout.)

–9–

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