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TIDA-00281: Why Galvanic Isolation is not used in this design

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Replies: 6

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Part Number: TIDA-00281

In TIDA-00281 i have observed that Driver Board Ground(GND_B) is common with the External MSP Launch Pad.

As per my understanding Launch Pad Ground and Driver Ground(GND_B) must be Separated or Isolated by galvanic isolation for safety and reliability.

Why this kept common in this design?


As we know ,when MOSFET switch there will be switching noise in ground and that Noise might go to Lauch Pad and can Reset MCU or can damage it if Spikes have enough high voltage.

(1)Why Ground Kept common in TIDA-00281?

(2)When to have galvanic isolation between Launch Pad and driver Card like opto coupler etc? any Special Considerations?

 additionally with this i have one more concern which i am describing below.

Let's say i have used Galvanic isolation between Lauch Pad and Driver card by Opto-coupler. With this configuration how can i manage Voltage and Current sense signals.

 

  • Hello Abhi, 

    at TI, we typically speak about two kinds of galvanic isolation:

    • Basic isolation - this prevents hazardous voltage entering the low-voltage circuitry during an error event. There is also a reinforced isolation which is double the basic isolation.
    • Functional isolation - this isolation is required to achieve the desired functionality. This isolation prevents noise coupling, breaks grounding loops etc.

    Typical 12/48-V automotive systems do not require basic isolation because voltages are not lethal. The requirement for functional isolation varies from region to region. I've been seeing projects with both. The final decision depends on the OEM and system concept on the vehicle level (if we still speak automotive). Nevertheless, the communication interface is often isolated in order to prevent noise coupling to the communication wires.

    I have not worked with TIDA-00281 but I am quite sure that the author was able to maintain noise levels on reasonable level which allowed him to avoid the isolation. If you want to implement isolation, TI offers a broad portfolio of isolators you may like:

    • Digital isolators (e.g. ISO77xx)
    • Isolation amplifiers (e.g. AMC1301)

    Just go to  for more details. Note that we do not use opto devices but capacitive technology. The problem with traditional optocouplers is that they suffer from unpredictable aging factor. This make it difficult for the automotive use. 

    Please note that most, if not all, reference designs at ti.com do not demonstrate the final product. It is close but we test only conditions which are described in the design guide. Such a design demonstrates a silicon chip and highlights some of its features.

    For this reason, we often use EVMs like ControlBoards or LaunchPads because they are the easiest way how to add inteligence to the system and interface with the demonstrated chip (e.g. gate driver) or subsystem (e.g. motor control)

    Regards, Jiri Panacek

  • Just to add to what Jiri said, this design uses a Launchpad to allow for changing the microcontroller based on any designer's preferred MCU.  Typically the MCU would be on the board, so it would share a ground with either the 12V system or the 48V system.  Because there are many more interconnections on the 48V side, it is more cost-effective to put the MCU on the 48V side, and thus only need isolation for the three CAN signals TX and RX and STB.

    -- Clark Kinnaird

  • In reply to Clark Kinnaird:

    I am building Motor Driver card for Electric Vehicle.

    BLDC Motor is rated at 60V/250W and i have taken reference of TIDA-00281 to build motor driver card.

    Do i require any isolation in this system.I have not used CAN interface as i don't need.Also i haven't used flyback section because all the voltages are available with us.

  • In reply to Abhi Choksi:

    Hi Abhi,

    In my opinion, the isolation is not required in your application. Output power rating is rather low and for this reason, I don't expect any troubles. Of course, proper PCB layout and engineering techniques (e.g. bypass capacitors) are expected.

    Regards, Jiri

  • In reply to Jiri Panacek85:

    In same application do i require to isolate PWM signals from launch pad?

    On what basis you decide that this system require isolation or not.

    I want to know more in details for this.

  • In reply to Abhi Choksi:

    Abhi, 

    it is impossible to answer your question without knowing the end-application in details. Your motor drive is extremely small. Smaller the drive is, more likely it avoids galvanic isolation. As mentioned before, the need for basic isolation comes from regulations which vary with the market/region.

    The consideration for the functional isolation starts with the system level, for example:

    • is the motor drive in the motor compartment?
    • are there any communication interfaces?
    • what are the operating conditions? Does the drive work when the car drives or only when stationary?
    • is there a risk of ground loops? 
    • what happens when one power terminal looses connection 
    • etc. etc. etc.

    This is given by the system architects (OEMs) and I am not qualified to give any detailed guidance.

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