ISO122

www.ti.com

SBOS160A – NOVEMBER 1993 – REVISED JANUARY 2015

8.4 Device Functional Modes

The ISO122 does not have any additional functional modes.

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

9.1.1 Carrier Frequency Considerations

The ISO122 amplifier transmits the signal across the isolation barrier by a 500kHz duty cycle modulation

technique. For input signals having frequencies below 250 kHz, this system works like any linear amplifier. But

for frequencies above 250 kHz, the behavior is similar to that of a sampling amplifier. The signal response to

inputs greater than 250 kHz performance curve shows this behavior graphically; at input frequencies above

250 kHz the device generates an output signal component of reduced magnitude at a frequency below 250 kHz.

This is the aliasing effect of sampling at frequencies less than two times the signal frequency (the Nyquist

frequency). At the carrier frequency and its harmonics, both the frequency and amplitude of the aliasing go to

zero.

9.1.2 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 250 kHz, the output also will display spurious outputs (aliasing), in a manner similar to

that for VIN > 250 kHz and the amplifier response will be identical to that shown in the Signal Response to Inputs

Greater Than 250-kHz 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 vs Frequency

curve and compute the amplifier response to this input-referred error signal from the data given in the Signal

Response to Inputs Greater than 250-kHz performance curve. For example, if a 800-kHz 1000-Vrms IMR is

present, then a total of [(–60 dB) + (–30 dB)] x (1000 V) = 32-mV error signal at 200 kHz plus a 1 V, 800-kHz

error signal will be present at the output.

9.1.3 High IMV dV/dt Errors

As the IMV frequency increases and the dV/dt exceeds 1000 Vµs, 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 ±15 V

may decrease the dV/dt to 500 V/µs for typical performance.

9.1.4 High Voltage Testing

Texas Instruments has adopted a partial discharge test criterion that conforms to the German VDE0884

Optocoupler Standards. This method requires the measurement of minute current pulses (< 5 pC) while applying

2400-Vrms, 60-Hz high-voltage stress across every ISO122 isolation barrier. No partial discharge may be

initiated to pass this test. This criterion confirms transient overvoltage (1.6 × 1500 Vrms) protection without

damage to the ISO122. Lifetest results verify the absence of failure under continuous rated voltage and

maximum temperature.

This new test method represents the “state of the art” for nondestructive high–voltage reliability testing. It is

based on the effects of nonuniform fields that exist in heterogeneous dielectric material during barrier

degradation. In the case of void nonuniformities, 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 ms current pulses that repeat on each AC voltage cycle. The minimum

AC barrier voltage that initiates partial discharge 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.” The

Copyright © 1993–2015, Texas Instruments Incorporated

Submit Documentation Feedback

9

Product Folder Links: ISO122