7

®

ISO124

1

2

7

9

10

8

PGA102

ISO124

ISO150

1

2

3

16

4

6

7

8

5

15

15

+15V –15V

+15V –15V

V

IN

V

OUT

A

0

A

1

above 250kHz, the behavior is similar to that of a sampling

amplifier. The signal response to inputs greater than 250kHz

performance curve shows this behavior graphically; at input

frequencies above 250kHz the device generates an output

signal component of reduced magnitude at a frequency

below 250kHz. This is the aliasing effect of sampling at

frequencies less than 2 times the signal frequency (the

Nyquist frequency). Note that at the carrier frequency and its

harmonics, both the frequency and amplitude of the aliasing

go to zero.

ISOLATION MODE VOLTAGE INDUCED ERRORS

IMV can induce errors at the output as indicated by the plots of

IMV vs Frequency. It should be noted that if the IMV frequency

exceeds 250kHz, the output also will display spurious outputs

amplifier response will be identical to that shown in the “Signal

Response to Inputs Greater Than 250kHz” typical performance

curve. This occurs because IMV-induced errors behave like input-

referred error signals. To predict the total error, divide the isolation

voltage by the IMR shown in the “IMR versus Frequency” typical

performance curve and compute the amplifier response to this

input-referred error signal from the data given in the “Signal

Response to Inputs Greater Than 250kHz” typical performance

curve. For example, if a 800kHz 1000Vrms IMR is present, then

a total of [(–60dB) + (–30dB)] x (1000V) = 32mV error signal at

200kHz plus a 1V, 800kHz error signal will be present at the

output.

HIGH IMV dV/dt ERRORS

As the IMV frequency increases and the dV/dt exceeds

1000V/

µs, the sense amp may start to false trigger, and the

output will display spurious errors. The common-mode

current being sent across the barrier by the high slew rate is

the cause of the false triggering of the sense amplifier.

Lowering the power supply voltages below

±15V may

decrease the dV/dt to 500V/

µs for typical performance.

HIGH VOLTAGE TESTING

Burr-Brown Corporation has adopted a partial discharge test

criterion that conforms to the German VDE0884 Optocou-

pler Standards. This method requires the measurement of

minute current pulses (<5pC) while applying 2400Vrms,

60Hz high voltage stress across every ISO124 isolation

barrier. No partial discharge may be initiated to pass

this test. This criterion confirms transient overvoltage

(1.6 x 1500Vrms) protection without damage to the ISO124.

Lifetest results verify the absence of failure under continu-

ous rated voltage and maximum temperature.

This new test method represents the “state-of-the art” for

non-destructive high voltage reliability testing. It is based on

the effects of non-uniform fields that exist in heterogeneous

dielectric material during barrier degradation. In the case of

void non-uniformities, electric field stress begins to ionize

the void region before bridging the entire high voltage

barrier. The transient conduction of charge during and after

the ionization can be detected externally as a burst of 0.01-

0.1

µs current pulses that repeat on each ac voltage cycle.

The minimum ac barrier voltage that initiates partial dis-

charge is defined as the “inception voltage.” Decreasing the

barrier voltage to a lower level is required before partial

discharge ceases and is defined as the “extinction voltage.”

We have characterized and developed the package insulation

processes to yield an inception voltage in excess of 2400Vrms

so that transient overvoltages below this level will not

damage the ISO124. The extinction voltage is above

1500Vrms so that even overvoltage induced partial dis-

charge will cease once the barrier voltage is reduced to the

1500Vrms (rated) level. Older high voltage test methods

relied on applying a large enough overvoltage (above rating)

to break down marginal parts, but not so high as to damage

good ones. Our new partial discharge testing gives us more

confidence in barrier reliability than breakdown/no break-

down criteria.

FIGURE 3. Programmable-Gain Isolation Channel with

Gains of 1, 10, and 100.

FIGURE 2. Basic Signal and Power Connections.

+V

S1

+V

S2

Gnd

Gnd

V

IN

V

OUT

–V

S1

±V

S1

±V

S2

–V

S2

1µF

1µF 1µF

1µF

Isolation Barrier

ISO124