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Digital isolator ISO7220C

Julien Djn
Intellectual 810 points
Other Parts Discussed in Thread: ISO7220C, ISO7320C, ISO7821, ISO7841, ISO7842

Hello,

I use the ISO7220C digital isolator to separate my micro-controller part (F28335) from my power part (IGBT inverter). So isolators are used to propagate the PWM IGBT commands from the DSP to the inverter.

My typical DC voltage is around 600V (three-phased 400Vac / 50Hz network, rectified throught a diode rectifier, then filtered).

I an currently experiencing some EMI effects when working at 600V : inverter's IGBT drivers seem to be disturbed and commute in an erratic way, inducing the drivers in error state.

When I work at 320V (monophased voltage rectified), I have no problem.

Previously I used no isolators for PWM signals, and got similar problems but at much lower voltages (at ~100V the problem begun) ; thats why I added the isolator : that solved the problem until 320V, but now that appear again at 600V...and I have no DC supply to check the behavior with DC voltage in the interval  320V/600V.

Reading carefuly at the isolator datasheet, I found the Maximum Working Insulating Voltage to be 560Vpeak, so just a little bit under 600V.

Is it possible that this isolator is not the correct one to work under 600Vdc ?

Shall I change for an isolator with re-inforced isolation (like the ISO7521CDW) ?

Thank you,

Best regards,

Julien

  • 0
    TI__Genius 10005 points

    For lower EMI, I'd like to suggest ISO7320C which is pin compatible with ISO7220. ISO7320C also has max working voltage of 566 Vpk, so slightly lower than 600 Vdc but it should be able to withstand 600 Vdc without any issues.

    I'f you'd like to use a device with much higher working voltage with lower EMI, then I'd like to suggest ISO7821, ISO7841 or ISO7842. They are all in a bigger wide-body SOIC-16 package though.

  • 0 in reply to Saleem Marwat
    Intellectual 810 points
    OK, thanks for your answer.

    Do you think that adding 6V on the max working voltage can solve the issue ? Or you presume that ISO7320C has a better immunity than the ISO7220C ?

    Can you confirm that the ISO7320C is adapted for PWM signals at 10kHz, used to command IGBT ?

    Regards,
    Julien
  • 0 in reply to Julien Djn
    TI__Intellectual 2200 points

    Julien,

    ISO73xx and ISO78xx are both suitable for driving PWM signals at 10kHz.

    To add to Saleem's comments, since the problem you are facing appears to be an immunity issue, maybe due to Common Mode Transient Immunity, it is possible ISO7320 may not solve it. It maybe better to use one of the ISO78xx devices:  ISO7821, ISO7841 or ISO7842.

    Rgds,

    Anant

  • 0 in reply to Anant Kamath
    Intellectual 810 points
    I will first try with the ISO7320C, as it is compatible with my PCB made for ISO7220C.

    If not successful, I will test with the ISO7841 and ISO7842.

    I will keep you informed of the results,

    Thank you for your help !

    Regards,
    Julien
  • 0 in reply to Julien Djn
    Intellectual 810 points
    Hello,

    I changed my isolators for the ISO7320C : results are really better, but I still have sometimes EMI problems (inverter bridge that comes in error mode).

    I made a new PCB to use the ISO7842, but results are worst than with the ISO7320C althought the PCB layout are similar in both cases (I only adapted the isolator foot print and add the pull-up for enable signal). The main difference is that the PCB with ISO7320C is more "industrial" than the one with ISO7842 (that is more "prototype") : do you think it can be the reason why ISO7842 are worst than ISO7320 ?

    Thank you,
    Best regards,
    Julien