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Problems with AC244005 isolator

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lmeiners
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2011/01/31 16:10:01 (permalink)
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Problems with AC244005 isolator

We're developing a line of motor drives that have the circuit common of the dsPIC33 processor at the same potential as the negative side of the DC bus.  When we tried to debug these systems using the AC244005 isolators that are an accessory to the REAL ICE emulator pods, we would get random faults in the debugger as soon as we increased the bus voltage above about 50V (that's with the IGBT switches operating).  After trying about every type of isolation we could think of, we eventually attributed the problem to the approximately 460pF of coupling capacitance between the high and low voltage sides of the isolator, which was coupling the high-frequency noise from the DC bus back into the emulator and causing communication errors.  We took the circuit that Microchip used for the isolator and did our own layout of the board  The coupling capacitance in the new layout dropped to about 10pF and the problems that we were having went away.  We suggested to the technical support group that it would be a good idea for them to do a new layout of the board and offered to give them what we had done.  Haven't had a response so far.  If anyone is having similar problems we're willing to share the Gerber files and BOM if anyone wants to make their own board.  Perhaps the moderator could respond if Microchip would have a problem with this.
#1

15 Replies Related Threads

    flubydust
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    Re:Problems with AC244005 isolator 2011/01/31 20:09:22 (permalink)
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    How on earth did they manage to get 460pF of stray capacitance across an isolation barrier?

    You need about 8 square inches of plate to get 460pF with 0.4mm FR4 dielectric.

    Did they have a multilayer board with a large area of 'hot' and 'cold' plane overlapping? It sounds dangerous never mind noisy.

    post edited by flubydust - 2011/01/31 20:12:11
    #2
    lmeiners
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    Re:Problems with AC244005 isolator 2011/02/01 08:29:55 (permalink)
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    flubydust

    How on earth did they manage to get 460pF of stray capacitance across an isolation barrier?

    You need about 8 square inches of plate to get 460pF with 0.4mm FR4 dielectric.

    Did they have a multilayer board with a large area of 'hot' and 'cold' plane overlapping? It sounds dangerous never mind noisy.


    I think, all true.  There are a lot of areas where the separation between the high-voltage and low-voltage copper is about 10 mil.
    #3
    SHRIPAD
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    Re:Problems with AC244005 isolator 2012/07/20 05:12:35 (permalink)
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    Dear Imeiners,
              We are also using dsPIC33F for motor control application. We are having 380V DC Bus on our Board & also having an ICD3 Debugger & we need to isolate debugger from our target. Please can you let me know whether it is possible to use your Isolator or AC244005 with ICD3 or it is only meant for Real ICE?
    It would be very kind of you if you can share gerber files & BOM of your Isolator. If this can't help our cause please can you suggest any alternate solution.
     
    Waiting for your valuable reply. Thanks in Advance.
    Regards,
    Shripad
    #4
    Antipodean
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    Re:Problems with AC244005 isolator 2012/07/20 08:33:19 (permalink)
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    lmeiners 
    If anyone is having similar problems we're willing to share the Gerber files and BOM if anyone wants to make their own board.  Perhaps the moderator could respond if Microchip would have a problem with this.


    I wouldn't mind having a copy, if possible please.

    Do not use my alias in your message body when replying, your message will disappear ...

    Alan
    #5
    jswanson
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    Re:Problems with AC244005 isolator 2012/08/09 02:41:51 (permalink)
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    I would like a copy also please.  I was wondering if the circuit could be modified to provide VPP for devices that require it?
    #6
    drazen
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    Re:Problems with AC244005 isolator 2012/08/09 07:39:04 (permalink)
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    SHRIPAD
    Dear Imeiners,
             We are also using dsPIC33F for motor control application. We are having 380V DC Bus on our Board & also having an ICD3 Debugger & we need to isolate debugger from our target. Please can you let me know whether it is possible to use your Isolator or AC244005 with ICD3 or it is only meant for Real ICE?
    It would be very kind of you if you can share gerber files & BOM of your Isolator. If this can't help our cause please can you suggest any alternate solution.

    Waiting for your valuable reply. Thanks in Advance.
    Regards,
    Shripad

     
    AC244005 is strictly for RealICE. It is not USB isolator but sits between ICSP and RealICE input. RealICE is using LVDS for signaling and this isolator isolates those LVDS signals.
     
    You could try to use any USB isolator. AD has some USB isolator chips.
    #7
    Slog_On
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    Re:Problems with AC244005 isolator 2014/09/07 14:27:24 (permalink)
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    With hopes that you are still around, do you still have a copy of the AC244005 rebuild data?
    And even if not, could you point to an on-line schematic?  we have inherited an isolator that doesn't work and need to troubleshoot it.
    Thanks in advance.
    #8
    drazen
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    Re:Problems with AC244005 isolator 2014/09/09 02:16:51 (permalink)
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    I think isolator schematic is part of (newer) RealICE datasheet. Open RealICE pages on microchip and take a look into pdfs.
    #9
    Daimonion
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    Re:Problems with AC244005 isolator 2014/11/27 08:43:14 (permalink)
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    Regarding this schematics, drazen
     
    may it is possible to take a closer look into this problems:
     

    #10
    ric
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    Re:Problems with AC244005 isolator 2014/11/27 12:38:11 (permalink)
    +1 (1)
    Daimonion
    Regarding this schematics, drazen
     
    may it is possible to take a closer look into this problems:




    It appears you may have tried to post a URL, which the forum has not allowed.

    I also post at: PicForum
    Links to useful PIC information: http://picforum.ric323.co...opic.php?f=59&t=15
    NEW USERS: Posting images, links and code - workaround for restrictions.
    To get a useful answer, always state which PIC you are using!
    #11
    Daimonion
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    Re:Problems with AC244005 isolator 2014/11/27 12:41:37 (permalink)
    +1 (1)
    Hm the forum does not allow his own links?!
     
    http://www.microchip.com/forums/m834320.aspx

     
    post edited by Daimonion - 2014/11/27 12:45:44
    #12
    DarioG
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    Re:Problems with AC244005 isolator 2014/11/27 14:54:55 (permalink)
    +1 (1)
    It only depends on your score/youth grin

    GENOVA :D :D ! GODO
    #13
    ric
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    Re:Problems with AC244005 isolator 2014/11/27 14:56:07 (permalink)
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    Youth?
    Do you mean "age" on this forum? :)

    I also post at: PicForum
    Links to useful PIC information: http://picforum.ric323.co...opic.php?f=59&t=15
    NEW USERS: Posting images, links and code - workaround for restrictions.
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    #14
    DarioG
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    Re:Problems with AC244005 isolator 2014/11/27 14:59:58 (permalink)
    +2 (2)
    yeah, tried to be funny grin !!

    GENOVA :D :D ! GODO
    #15
    lmeiners
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    Re: Problems with AC244005 isolator 2015/01/29 12:04:48 (permalink)
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    My apologies.  I haven't looked at this thread for a looong time.  The circuit files for our layout of the isolator are attached.  As you will see, we basically copied the circuit given in the REAL ICE manual.  We left out the USDO and USCK signals.  It was our understanding that they weren't used, since trace is not supported with the isolator.  We could probably have squeezed them in but we didn't want to take the chance of crowding the areas around the small switching power supplies and picking up noise from them.  That's probably not an issue--we just didn't want to have to do the board over again.  The board fits in the Microchip box for the AC244005 isolator.  We put in the option of using a modular connector for the connection to the target.  Those don't become disconnected so easily.
     
    I gave this to Microchip shortly after the post and they sent me a couple of T-shirts and some other bling which was nice of them.  I don't know if they ever fixed the problem since we haven't purchased any more isolators since then.   I also can't guarantee if the circuit will work with the current version of their REAL ICE + isolator.  I tried to upload the schematics that go with this, which are *.pdf files, but they exceeded the 200K limit.  If anyone really wants them I'll disassemble the individual sheets and try again.
     
    Cheers
     
     
    #16
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