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How can I evaluate the isolated voltage in application from the safty standard(VDE, CSA, UL)?

Other Parts Discussed in Thread: ISO7220C, ADS1203, AMC1200

For example, in ISO7220C,

I can find VDE, CSA, and UL information, and in VDE(IEC 60747-5-2),

Basic Insulation

  Maximum Transient Overvoltage, 4000 VPK

  Maximum Surge Voltage, 4000 VPK

  Maximum Working Voltage, 560 VPK

But I cannot find any test or apply information of the three parameters, so I cannot determine the isolated voltage in real application.

And from the three parameter, I guess the test signal is AC voltage,

but how can I evaluae it when I apply ISO7220c in isolated DC voltage?

  • I'm not sure I understand your first question. ISO7220C is certified to withstand 4000Vpk transient Overvoltage for 60 seconds. It also passed 4000Vpk Surge (1.2usec/ 50usec waveform) voltage. The max working voltage indicates that this device can sustain 560Vpk voltage between the two grounds for the lifetime (28 years) of the isolator.

    The testing is performed with AC voltage. AC voltage is more stringent on the isolatin barrier when compared to the DC voltage.

  • Even though from isolation barrier perspective, AC is more stringent than DC voltage, we don't recommend this isolator for DC isolation due to functional performance risks associated with charge spreading.

     

  • Thanks, It's all I need. Sorry for the un-clear question.

  • for this answer : we don't recommend this isolator for DC isolation due to functional performance risks associated with charge spreading.

    So Can I guess all capacitive isolators are not suitable for DC isolation?

    In motor control, ADS1203+ISO7220 or AMC1200 are recommended for current measurement and bus voltage measurement(~400V), when the IGBT is failed in current measurement, or  the divided resistor for bus voltage measurement is broken, the isolator barrier endure 400VDC for long term. the AMC1200's insulation spec is: Viorm = 1200Vpk(AC), but I'm pullzed for your DC isolation description.

  • No,  this is not true for all capacitive isolators, we need to analyze performance on a device by device basis. As I mentioned earlier, the isolation barrier will remain intact under DC voltage stress. The only question is regarding the functionality  (parametric performance) of a specific device under a high electric field induced due to DC voltage. We just don't have enough DC stress data on some of these older devices.

    In your application, I don't see a problem with using our device since the isolation barrier will remain intact for the lifetime of the digital isolator (>28 years) under 400VDC stress.

  • Thanks. It's looks like some difficult for different isolator application.

    I find some isolator application document in TI.com, like:

    slla181a.pdf, ISO72x Digital Isolator Magnetic-Field Immunity
    slla198.pdf, The ISO72x Family of High-Speed Digital Isolators
    slla197.pdf, High-Voltage Lifetime of the ISO72x Family of Digital Isolators

    Maybe you can give me some other document which can help me.

     

  • Hi Bo,

    I've no specific document on DC isolation. Perhaps, it'll be easier if we can discuss your concerns over the phone. You can call me at 1-214-212-2250