Follow TI's high voltage technology experts to learn about the advantages of capacitive isolation technology!

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Follow TI's high voltage technology experts to learn about the advantages of capacitive isolation technology! [Copy link]

 Texas Instruments' reinforced isolation technology is achieved by connecting a thick silicon dioxide capacitor bank in series. Each channel uses high voltage isolation capacitors on both dies.

Cross-Section Schematic

In the cross-section schematic above, you can see that there is a die on each side, and both have a high voltage capacitor. And they are in series. The isolation capacitor bank is >21 microns thick. Data travels across this isolation barrier as shown in the schematic below. The signal comes in, is modulated, travels across the isolation barrier of the differential capacitor pair, is demodulated, and then travels out

This isolated communication path is used in digital isolators, isolated links, analog-to-digital converters, isolated amplifiers, and isolated gate drivers. This structure allows for very high isolation capabilities, including 12.8kV surge voltage rating, 8kV peak transient overvoltage, and 1.5kVRMS working voltage. Now let's take a closer look at the structure. We'll start at the top. Here's what you see in an X-ray image of a 16-lead SOIC package. This is a wide-body package. Inside the package, there is a large internal gap between the two die pads, which is over 600 microns. Each die has high voltage capacitors. This is a three-channel isolator with six capacitors on each side. The reinforced isolation barrier consists of two high voltage capacitors, one on each die in series. Each capacitor is a thick silicon dioxide capacitor dielectric. One of the best tests for high isolation voltage capability is the breakdown voltage test, or ramp-to-breakdown voltage test. In this test, a high AC voltage is applied from left to right. The voltage is ramped at a rate of 1 kVRMS per second until breakdown occurs. When breakdown occurs, the breakdown voltage is recorded. This process is repeated on a large number of devices. By statistically analyzing these devices, we can evaluate how well the technology performs relative to the rated value. In the histogram above, we have data from 1,130 devices from 113 lots that were ramped up to breakdown voltage. You can see that the average breakdown voltage is above 14kVRMS. This is much higher than the rated isolation voltage of 5.7kVRMS. A good way to judge how much higher this performance is is the CPK metric. A CPK of 1 means the data is 3sigma above the isolation requirement. A CPK of 2 means the data is 6sigma above the isolation rating. You can see that this data set has CPKs greater than 6. This CPK was measured under production test conditions and is 20% higher than the isolation rating. This data shows that TI's reinforced isolation portfolio has high voltage capabilities that exceed the reinforced isolation requirements. Reliability Testing The primary isolation electrical life test is the time-dependent dielectric breakdown test, or TDDB. TDDB is a standard method for determining dielectric life as a function of voltage. In the graph below, you can see that the voltages used for testing are the blue dots, and these are 5,000, 6,000, and 7,000 VRMS, which are much higher than the 1,500 VRMS operating voltage. Using Weibull statistics at each voltage, we can measure the average lifetime, which is called t63, or the point at which 63% of the devices fail. The points in the lifetime where the failure rate of the devices is still below 1 PPM form the dashed line on the left side of the graph. The multiple voltage data is then fit to a model. The model is a standard TDB model where the time to failure is exponentially related to the applied electric field, or in this case, the applied voltage. Because of the exponential relationship, you can see in the graph that the lifetime on the y-axis is a logarithmic scale, and it spans a wide range, from 10 seconds at the bottom of the graph all the way up to 300 years at the top of the graph. One way to use this data is to compare the 1 PPM line to the isolation rating. You can see a comparison of the two in the upper left corner of the graph. There are three ways you can compare the margin of the actual data to the working voltage. One is the voltage margin. Another is the lifetime margin. The last is to look at the failure rate. We chose silicon dioxide as our dielectric because it has excellent reliability. In the table below, we compare some dielectrics that are sometimes used in isolation products.

• Surge Testing

Surge testing is used to verify the device's ability to withstand very high voltage levels for a short period of time, such as lightning strikes. Surge peak voltage testing is required and is part of external standards IEC61000-4-5 and VDE0884-10 and 11. Surge testing is performed by sampling. At TI, we use a method to statistically analyze surge characterization data, as shown in the following figure: This figure shows the surge test failure rate as a function of voltage. The method we use is to test a certain number of devices at different voltages and record the number of failures. This test uses 50 pulses with the same polarity. We call this a unipolar surge test. We test with 50 positive pulses or 50 negative pulses. The unipolar test represents immunity to a single surge event. However, there is another test method, which we call bipolar testing. The bipolar test is a worst-case surge test due to hysteresis effects. In this test, each device is subjected to 25 pulses of opposite polarity in sequence. When we switch polarity, the device still has some of the charge caused by the previous 25 pulses, which puts more stress on the isolation barrier. This test represents immunity to more complex surge events. This test is now required by VDE0884-10 and 11. The orange data in the figure is bipolar data, and with this data, you can see that the failure rate is zero at 12kV, and the failure rate is still not zero until 15kV, and then there are failures after the voltage is higher, and the failure rate is 100% at 22kV. At some voltages, all isolation layers will fail. This type of test helps you understand how much margin your technology has relative to the required value. In this case, you can see that the guaranteed voltage is 12.8kV, which is 60% higher than the 8kV surge isolation rating. This data shows that the device has a very high margin relative to the required isolation voltage. In summary, TI's reinforced isolation product portfolio has high voltage capabilities that exceed the reinforced isolation requirements. We use statistical testing methods to prove the high voltage isolation quality of these products with substantial margins.

qwqwqw2088

By the way, learn about the advantages of capacitive isolation technology

star_66666

Good information, good stuff.

alan000345

qwqwqw2088 Published on 2018-12-12 12:03 By the way, let’s learn about the advantages of capacitor isolation technology

Yes, the isolated ones are better in terms of safety, but now many manufacturers do not provide isolated ones due to cost issues.

alan000345

star_66666 posted on 2018-12-12 23:39 Good information, good stuff

I will share more good things like this in the future.

star_66666

Look forward to it, come on