®

ISO212P

7

The bulk inception voltage, on the other hand, varies with

the insulation system and the number of ionization defects.

This directly establishes the absolute maximum voltage

(transient) that can be applied across the test device before

destructive partial discharge can begin.

Measuring the bulk extinction voltage provides a lower,

more conservative, voltage from which to derive a safe

continuous rating. In production, it’s acceptable to measure

at a level somewhat below the expected inception voltage

and then de-rate by a factor related to expectations about the

system transients. The isolation amplifier has been exten-

sively evaluated under a combination of high temperatures

and high voltage to confirm its performance in this respect.

The ISO212P is free of partial discharges at rated voltages.

PARTIAL DISCHARGE TESTING IN PRODUCTION

Not only does this test method provide far more qualitative

information about stress withstand levels than did previous

stress tests, but it also provides quantitative measurements

from which quality assurance and control measures can be

based. Tests similar to this test have been used by some

manufacturers such as those of high voltage power distribu-

tion equipment for some time, but they employed a simple

measurement of RF noise to detect ionization. This method

was not quantitative with regard to energy of the discharge

and was not sensitive enough for small components such as

isolation amplifiers. Now, however, manufacturers of HV

test equipment have developed means to measure partial

discharge, and VDE, the German standards group, has adopted

use of this method for the testing of opto-couplers. To

accommodate poorly defined transients, the part under test is

exposed to a voltage that is 1.6 times the continuous rated

voltage and must display < 5pC partial discharge level in a

100% production test.

INSTALLATION AND

OPERATING INSTRUCTIONS

POWER SUPPLY AND SIGNAL CONNECTIONS

As with any mixed analog and digital signal component,

correct decoupling and signal routing precautions must be

used to optimize performance. Figure 1 shows the proper

passed to Com 2 with a 0.1

µF ceramic capacitor as close to

the device as possible. Short leads will minimize lead

inductance. A ground plane will also reduce noise problems.

If a low impedance ground plane is not used, signal common

lines, and either O/P High or O/P Low pin should be tied

directly to the ground at the supply and Com 2 returned via

a separate trace to the supply ground.

To avoid gain and isolation mode (IMR) errors introduced

by the external circuit, connect grounds as indicated in

Figure 3. Layout practices associated with isolation amplifi-

ers are very important. In particular, the capacitance associ-

ated with the barrier, and series resistance in the signal and

reference leads, must be minimized. Any capacitance across

the barrier will increase AC leakage and, in conjunction with

ground line resistance, may degrade high frequency IMR.

VOLTAGE GAIN MODIFICATIONS

The uncommitted operational amplifier at the input can be

used to provide gain, signal inversion, active filtering or

current to voltage conversion. The standard design approach

for any op-amp stage can be used, provided that the full scale

voltage appearing on f

If the input op-amp is overdriven, ripple at the output will

result. To prevent this, the feedback resistor should have a

minimum value of 10k

Ω.

Also, it should be noted that the current required to drive the

equivalent impedance of the feedback network is supplied

by the internal DC/DC converter and must be taken into

account when calculating the loading added to

±V

Since gain inversion can be incorporated in either the input

or output stage of the ISO212P, it is possible to use the input

amplifier in a non-inverting configuration and preserve the

high impedance this configuration offers. Signal inversion at

the output is easily accomplished by connecting O/P High to

Com 2 instead of O/P Low.

ISOLATED POWER OUTPUT DRIVE CAPABILITY

On the input side of the ISO212P, there are two power

supplies capable of delivering 5mA at

±8V to power exter-

nal circuitry. When using these supplies with external loads,

it is recommended that additional decoupling in the form of

10

µF tantalum bead capacitors be added to improve the

voltage regulation. Loss of linearity will result if additional

filtering is not used with an output load. Again, power

dissipated in the feedback loop around the input op amp

must be subtracted from the available power output at

±V

SS1.

If the ISO212P is to be used in multiple applications, care

should be taken in the design of the power distribution

FIGURE 3. Technique for Connecting Com 1 and Com 2.

V

ISO

CC

+V

CC

–V

Power

Supply

Load

Circuit

R

O/P Low

Com 2

Com 1

Input

Common

C

INT

C

EXT 2

C

EXT 1

O/P High

C

and R have a direct effect.

EXT 2

C

has minimal effect on total IMR.

EXT 1

f

B

–

+