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Digital isolator problems

redflood
Intellectual 780 points

Other Parts Discussed in Thread: ISO5851, ISO7420, ISO7320FC, ISO7420FCC, ISO7240CF

Hi everyone,

I want to use a digital isolator of TI (such as ISO742x) to make a safety board to protect MCU board and Motor driver board like an Opto-isolator. Is it possible, any risk to my MCU board? any warning for me?

Thanks!

  • 0
    TI__Prodigy 530 points
    Hi,
    Yes you can use digital isolators to protect your MCU. Isolated gate driver ISO5851 is available from TI. I can help you chose the best part, if you can provide below information.
    Do you intend to control motor driver from a MCU board and provide isolation & safety to MCU board? What are voltages at motor drive end, which you want to isolate from MCU board? Can you please clarify and share rough schematics or block diagram to better understand your query. Thanks
    Regards,Neer
  • 0 in reply to Neeraj Bhardwaj
    Intellectual 780 points

    Thank Neer,

    I want to use ISO7420 with diagram as below, I think it simple and easy to use, but can you help to advise about safety of that Idea?

  • 0 in reply to redflood
    TI__Genius 12185 points

    Hi,

    Typically, for many motor drive applications, it is recommended to use a digital isolator with default output state 'Low'. This is to ensure that during power up, the digital isolator doesn't turn on the IGBT or MOSFET inadvertently.

    Please check your system setup and confirm whether you need a device with default output 'Low' or 'High'. If default output low, then we recommend to use ISO7320FC or ISO7420FCC.

  • 0 in reply to Saleem Marwat
    Intellectual 780 points
    Yes I used ISO7420CF, It's work well, my concern is:
    1.is it has ability to protect my controller?
    2. Can I use it as a solution replace for opto coupler?
    3. When control pwm, we need ground from controller directly connect to ground of motor, this issue make me confuse, because we want to ground is separated with this solution, can you suggest to me a some ideas?
  • 0 in reply to redflood
    TI__Genius 12185 points
    Ok, great. I assume you are using ISO7420FCC (& not ISO7420CF since such a part doesn't exist).
    To answer your questions:

    1- Yes, it has the ability to protect your controller with in the isolation ratings of the device. ISO7420FCC has safety certifications from the following regulatory agencies: UL, VDE, CSA, and CQC. Safety certificates are available online at: www.ti.com/.../technicaldocuments uner 'More Literature' tab.

    2- Yes, you can use this device as an opto-replacement.

    3- Not sure what you mean. Can you send a drawing of how you are connecting the grounds together? GND1 of ISO7420FCC is typically connected to the low voltage side and GND2 is connected to high voltage system ground. It is similar to how you'd connect opto-coupler ground pins.
  • 0 in reply to Saleem Marwat
    Intellectual 780 points

    Sorry for my mistake, I used ISO7240CF.

    It's seem I solved almost my problems after your answer. Thanks a lot.

    New answer.

    1. When we use opto, we need resistor to have a right current, with my part my design as below:

    DIR, BREAK, PWM was connected to controller, is my design meet standards of TI?

    2. Pull up or pull out resistor will better?

    3. How about level protection of ISO7240CF part? Can you suggest another part with higher protection ? I'm going to make a new design with a CNC machine higher current and voltage. I need a 4 channels isolator of TI.

    Thanks for your help!

  • 0 in reply to redflood
    TI__Prodigy 530 points

    Hi,

    In your design, please make left and right side ground different as shown below from datasheet. Currently both side capacitors is showing connected to GND. Left side C211 is to be connected to GND1 and Right side C212 is to be connected to GND2.

    #1) DIR, BREAK, PWM inputs, driven from controller is fine. Please let's know input signal frequency; will be mostly within spec of 25Mbps.

    #2) Pull-up or pull-down is not needed from TI isolator point of view. In case it is needed from microcontroller point of view, then you can consider putting them accordingly.

    #3) Maximum working voltage is 560Vpk. For CNC machine, please let's know what are motor specifications;  e.g. if 48V with 2.5A rating stepper motor is considered, then it is well below allowed spec. In case you plan to use higher voltage and current motor, then you need to change H-bridge device accordingly, whereas isolation device can remain the same.

    Regards, Neer

  • 0 in reply to Neeraj Bhardwaj
    Intellectual 780 points
    Thank you for your support!
    1. When we use IGBT Gate Driver as you have suggested to me this part ISO5851?,
    2. how I can choose a right part for my application? which is important parameter?
  • 0 in reply to redflood
    TI__Prodigy 530 points

    Thanks.

    Please refer to application note for further details on Motor Driver and Control Solutions:  "http://www.ti.com/lit/sl/slyb165g/slyb165g.pdf".

    Regards, Neer

    PS: If this answers your question, please click verify answer to close this thread.

  • 0 in reply to Neeraj Bhardwaj
    Intellectual 780 points

    Thanks for your support!

    1.So with four Gate Drivers we have a H-Bridge, isn't it?

    2. I can connect a pin of controller has tolerance 3.3V or 5V to pin of ISO7240F, it's depend on VCC I source. am I right?

    3. I refer to slau253a.pdf, and below is reference design, some part is difference from typical design in datasheet of IC, so I want to know function of resistors R1,R2,R3,R4 and C1,C2,C3. is C8,C6,C7,C5 necessary ? can I use simple design like typical design?


    Thanks!

  • 0 in reply to redflood
    TI__Genius 12185 points

    Regarding your question # 3, ISO7240CF has 4000 Vpk Transient Overvoltage rating and 560 Vpk working voltage as Neer pointed out. If you need digital isolator with higher isolation rating, then you may want to consider ISO7840F. It has Transient Overvoltage rating of 8000 Vpk and working voltage of 2121 Vpk.

  • 0 in reply to Saleem Marwat
    Intellectual 780 points

    Thank you, I have update the latest questions. Can you or Neer give me an answer?

  • 0 in reply to redflood
    TI__Prodigy 530 points

    Hi,

    Please find response to your queries. Thanks

    #1) Yes, for further details please refer to application note http://www.ti.com/lit/sl/slyb165g/slyb165g.pdf.

    #2) Yes, it depends on VCC1 of Isolation device. Please refer to device datasheet of ISO7240CF for further details.

    #3) Yes, you can use simple design like typical design. R1,R2, R3 is for 50Ohms drive input source and not needed for microcontroller with CMOS output. C1, C2, C3 are load capacitance for testing and not needed. C5, C6, C7 and C8 are needed for power supply.

    Regards, Neer