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ISO122 Datasheet(PDF) 7 Page - Burr-Brown (TI) |
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ISO122 Datasheet(HTML) 7 Page - Burr-Brown (TI) |
7 / 13 page 7 ® ISO122 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 (aliasing), in a manner similar to that for V IN > 250kHz and the amplifier response will be identical to that shown in the Signal Response to Inputs Greater Than 250kHz 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 250kHz 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. Isolation Barrier V IN 1 µF +V S2 – V S1 +V S1 1 µF 1 µF Gnd –V S2 1 µF V OUT Gnd ±V S1 ±V S2 FIGURE 2. Basic Signal and Power Connections. 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 ISO122 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 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 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 ISO122. 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. ISO122P ISO150 A 1 A 0 –15V +15V +15V –15V 1 2 9 10 7 8 V OUT 2 1 15 15 16 PGA 102 7 6 8 V IN 3 4 5 FIGURE 3. Programmable-Gain Isolation Channel with Gains of 1, 10, and 100. |
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