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TPS61322: High-Frequency Switching Noise (Radiated EMI) is degrading receivers sensitivity.

Mehdi Noroozi
Prodigy 50 points
Part Number: TPS61322
Other Parts Discussed in Thread: TPS54240

A fix 5V boost converter (TPS613222A) has been used to supply a linear battery charger, which requires minimum 450mA input current. Boost converter's input voltage is 4V, which comes from a buck converter (TPS54240) with 3A maximum output current. To create the boost converter's schematic, Webench Power Designer has been used (Not for the layout). We have used two snubbers to reduce the noise, one across the diode (main snubber) and another one, which was optional between the SW node and GND pin. The layout, which has been implemented on a six-layer-board, also complies with the specifications and recommendations of component's data sheet, especially with regard to minimizing and optimizing the critical current path loops.

The 5V boost converter works as expected, and the component with external Schottky diode also delivers the expected minimum current; however, we have an EMC problem, because boost converter emits a high-frequency switching noise, which appears at the range of 1.5GHz. This has been degraded the sensitivity of both GNSS (1575.42MHz) and TPMS (433MHz) receivers, which are in two different bands. These functionalities are part of internal assembly and their sensitivity is significantly reduced when the boost converter is activated with the corresponding output load. 

So we want to know, which other measures should be taken here to minimize the radiated EMI?

Thank you for your support.

  • 0
    TI__Mastermind 21565 points

    Hi Mehdi:

    The layout is importance for a DCDC converter. May you share the layout with me?

    And adding the beads will do some help for you!

  • 0 in reply to Minqiu Xie
    Prodigy 50 points

    Hi Minqiu,

    Thank you for the initial feedback.

    As you requested, I sent you the layout so that you could also take a look at it.

    Best regards,

    Mehdi

  • 0 in reply to Mehdi Noroozi
    TI__Mastermind 21565 points

    Hi Mehdi:

    Sorry that I am out of office today. I'll back next week.

  • 0 in reply to Minqiu Xie
    TI__Mastermind 21565 points

    Hi Mehdi:

    Thanks for your kind waiting. I'm checking your message. And will reply soon. 

  • 0 in reply to Minqiu Xie
    Prodigy 50 points

    Hi Minqiu,

    Thank you very much for reviewing the layout.

    Regarding the EMI problem, we performed more measurements in the EMI test lab, that some of them were very promising.


    So to make sure that we have considered everything, I wanted to reach you once again and ask you some questions:

    1- With the same layout, we noticed that not fitting the external schottky diode is also reducing the radiated EMI. So now, we want to know whether it's possible to omit this diode without having any influence on the converter performance, especially in terms of power efficiency and thermal performance. What is the maximum output current of this component without engaging the optional schottky diode? I'm asking this because in the component's datasheet has been mentioned that basically an external schottky diode can support high output current applications; therefore, since we also wanted to have a 5V/450mA at the output, we also included it in our initial design.

    2- Additionally, we've also noticed that higher inductance values are also increasing the radiated EMI. In fact, by using a smaller inductance value (e.g. 1uH) we've got a better result; therefore, we also want to know what inductance values can be used in this application (Input: 3.9V, Output: 5V/450mA) so that component's thermal and efficiency performance could still be maintained in a an acceptable range? How the selection of inductance value can improve the radiated EMI? Is that possible to select smaller inductance values (e.g <1uH) as well? Does the minimal output capacitor value need to be recalculated again for new inductor?

    Thank you for your consideration.

    Best regards,

    Mehdi

  • 0 in reply to Mehdi Noroozi
    TI__Mastermind 21565 points

    Hi Mehdi:

    I have replied you via private massage. Please check that. :-)

  • 0 in reply to Minqiu Xie
    Prodigy 50 points

    Hi Minqiu,

    Thank you very much for the comments.


    We will take into account all the information you have provided us.

    Best regards,

    Mehdi