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SM320F28335-EP: Ferrites on Supply Lines

Dragos Moscalu
Prodigy 170 points
Part Number: SM320F28335-EP
Other Parts Discussed in Thread: TMDSCNCD28335,

Dear Ti support Team,

Checking the F28335controlCARD HWDevPkg PGF [R1.0] documentation, especially the TMDSCNCD28335 document number, where F28335 PGF/PTP microcontroller is used, I've noticed the integration of Ferrites on all power supply pins: L1-L18. The Ferrites together with C28 & C29 are creating a very efficient Low-Pass Filter for blocking the uC EMI noise, to be coupled back into the Power Supply lines.

In the current design, we plan to use the SM320F28335-EP microcontroller, and we would like to know the effects of Ferrites removal - on Electromagnetic Emission Noise.

1) Are these Ferrites mandatory to be used with SM320F28335-EP operating at 150MHz internal Clock ?

2) Are these Ferrites necessary on all Supply Pin Groups - VDIO33 / VDD18 / VDADC18 ?

3) In what frequency range these Ferrites are very efficient? Do you have some EMI results from the Demo Board, with / without Ferrites ?

Thank you for your support,

Dragos

  • 0
    TI__Mastermind 42195 points

    Dragos,

    these are not required, simply an attempt to mitigate some noise from entering the MCU's different power domains.

    I do not have any data on the effective frequency range or comparative EMI results with and without the filter. If you are interested in developing a filter for your system I would recommend contacting a Ferrite manufacturer for suggestions on how to mitigate the exact noise you will see in your system.

    Regards,
    Cody 

  • 0 in reply to Cody Watkins
    Prodigy 170 points

    I've found another answer on this Forum, that suggest to use Ferrites to protect the ADC supply lines, from noise generated by other supply lines.

    “The inductive bead pi-filters are there to reduce noise - between the analog and digital circuitry, but also to reduce noise from entering the main power supply.  Please note that the true needs for the F2837x's power supplies are shown in the device datasheet and that the inductive bead filters are not required.  A solid statement can be made for doing what you proposed and beads can cause issues if they're not used carefully.  Please note that the "best" power distribution network will often depend on the layout and the EMC requirements for the product being developed.  As a result, the product designer will often be the best at determining what "best" means.”

    https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/552735/ferrite-beads-on-the-vddio-and-vdd-pins/2020719?tisearch=e2e-quicksearch&keymatch=Ferrites%20C2000#2020719

    Could you confirm there will be no issue, on ADC acquisition after removing the Ferrites? I want to mention that in our design the same GND plane (Layer 2) is shared between VDIO33 / VDD18 and VDADC18. There is no plane separation for analog ADC area, from digital supply area.

    Thank you,

    Dragos

  • 0 in reply to Dragos Moscalu
    TI__Mastermind 42195 points

    Dragos,

    Adding a ferrite bead between the analog supply and other supplies is the most helpful place. This can help with getting good analog performance. It is recommended and can be very helpful in a noisy system particularly if the PCB layout is unideal. That being said using ferrite beads on the power supplies is not a requirement. You must evaluate your system needs here.

    It is very common to have a shared ground plane, which we show on many of our EVMs. Some EVMs will feature a partial ground split, but this practice can actually increase you're system noise if care is not take to avoid crossing the ground split with signals that may switch frequently.

    Please note that the ADC voltage reference is very important as well and is another point where noise can be directly coupled into your ADC results.

    Regards,
    Cody