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Original question:

DRV8353RS-EVM: Isolation interface

DRV8353RS-EVM: Isolation of DRV8353RS gate driver

Shaza Hany
Prodigy 40 points
Part Number: DRV8353RS-EVM
Other Parts Discussed in Thread: DRV8353R, ISO7761, ISOW7841, SN6501

Is the gate driver DRV8353R isolated or not? If not, What are the impacts of using it without isolation and how can we provide external protection or isolation.

  • 0
    TI__Guru 61280 points

    Shaza,

    Thanks for posting on the MD forum!

    The device is not isolated. Which nodes are you wanting to isolate?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 40 points

    Thank you for replying,

    I want to understand, is the MCU ground isolated from the system ground; and if not, what is the effect of this?

  • 0 in reply to Shaza Hany
    TI__Guru 61280 points

    Shaza,

    The DRV GND is connected directly to the FET bridge GND. You can isolate the MCU from the rest of the system if you choose.

    The reason the DRV is connected directly to the FET bridge is because this is how the DRV monitors the FETs and also how the DRV drives current into the FET gates and similar.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 40 points

    Do you have any recommendations for isolating the MCU?

  • 0 in reply to Shaza Hany
    TI__Guru 61280 points

    Shaza,

    I will forward your post to the isolation team.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    TI__Expert 6955 points

    Adam,

    We have digital isolators capable of isolating the 12 digital signals between the MCU and DRV. Unfortunately our digital isolators would not be able to isolate the current sense amp outputs (SOA, SOB, and SOC). For the isolating the digital signals, I recommend using two ISO7761 devices. Are you familiar with digital isolation in regards to PCB design and power supply?

    Respectfully,

    Lucas

  • 0 in reply to Lucas Schulte9
    TI__Genius 17100 points

    Hi Shaza,

    Hopefully all is well. Would you still like assistance isolating digital signals between the MCU and DRV as mentioned above? Current sense measurements can be isolated with Isolated amplifiers TI offers as described in this TI Design. Please let us know soon to prevent this thread from being closed due to inactivity.


    Thank you for your time,
    Manuel Chavez

  • 0 in reply to Lucas Schulte9
    Prodigy 40 points

    Could you please help with the digital isolation in regards to PCB design and power supply? I would appreciate very much.

  • 0 in reply to Shaza Hany
    TI__Genius 17100 points

    Hi Shaza,

    Of course!

    • PCBs can be designed with 2 or 4+ layers for isolation
    • Include a bank of 100nF, 1uF, and 10uF capacitors placed closely to the device power pins -- where 100nF is <2mm from Vccx pins followed by the 1uF cap and the 10uF is furthest -- as shown in the images below
    • 50Ω resistors can be included on the data lines' inputs for protection of emissions control
    • Enable pins should be pulled up to Vccx through a 4.7kΩ resistor if not digitally controlled
    • Via stitching can also be included to improve GND connections
    • Ensure there are no planes, traces, or vias on the isolation barrier as this compromises the isolator's function.





    Isolated power supplies can be derived based on your application's isolated load requirements: what is the estimated current load? For an isolator that can power itself and supply ~120mA for additional ICs, the ISOW78xx family of devices (including ISOW7841 shown above) might simplify the design, and for higher power requirements (1.75W - >5W), isolated power supplies can be designed using isolation transformer drivers like TI's SN6501 and SN6505. These devices are typically used as shown below:



    Please let me know if this information is helpful for your design.


    Thank you for your time,
    Manuel Chavez