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What is transient immunity?

Release time:

2023-05-31 10:37

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　　Things like transient immunity are basically products used in the industrial field, most of which we have never seen or heard of. You can say that they are not very common in life, but they also play an irreplaceable role in the industrial industry. So the first thing we should understand clearly in use is what the transient immunity is. Follow us to learn more about it.

 

瞬态抗扰度

 

　　So let's first look at the definition of transient immunity, which is the isolator's ability to suppress fast common-mode transients, usually in kV/µS. In industry, transient immunity is important because common-mode transients are one of the main causes of data corruption in isolated applications. In general, the test setup for the transient immunity we use and the schematic of the test plate photo will follow its schematic guide, and will also show the main parasitic coupling in the HCPL-4506 optical coupler. Transient immunity Because high voltage swing rate (high frequency) transients can be coupled through parasitic capacitors on the isolation gate, thus destroying the data. Then its single largest parasitic coupling in the transient immunity is CLEDN, especially when the photocoupler is configured in the ground cathode mode, it effectively shorts the impedance of the VCM, so the external pull-up resistor rather than the internal pull-up resistor is used for device testing. That is to say, the remaining parasitic coupling, albeit weak, can still produce the data errors caused by CMT. And to a small extent, it will increase the probability of data errors. Of course, it is also an optical coupler upgrade product, can directly replace the ordinary optical coupler, and does not need to make any changes to the PCB, can provide better performance and reliability and power efficiency. Internal puller resistors with transient immunity increase the probability of data errors due to CMT events in both the photocoupler and Si8712A, and since the parasitic coupling of CLED02 is weaker than that of CLED01, the stronger parasitic coupling of CLED01 is associated with a higher 20K. This shows the effect of a single parasitic event, but multiple couplings can combine to produce unwanted effects.

　　The photocoupler input inside the transient immunity keeps the logic high (output low), this time using a pull-up resistor inside for 20 kΩ. Its test results compare the CMTI performance of the Si8712A CMOS digital isolator and the HCPL-4506 optical coupler. At the same time, its LED cathode is exposed to a rise time of 40 ns CMT. This rise time will rapidly change the voltage of LED cathode and anode, thus causing parasitic current to be injected into the Vo pin through CLED02, but CLED01 inside transfers the current from IF to RL pin. And this "1-2" combination causes the current in both the LED and the internal pull-up resistor to decrease simultaneously, further reinforcing the instantaneous output shutdown.

Century Wisdom (Suzhou) Testing Technology Co., Ltd

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