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LTM8067 - Radiated Emissions

Hi, Looking at Radiated emissions of the LTM8067 with near field probe, I appear to be getting significant radiated emissions from the top of the device and out through input and output filter stages causing cross coupling onto nearby circuitry. The frequency is in the HF band around 8-10MHz which some I believe to be harmonics. Do you have any resource, Techniques or advice to improve the radiated emissions on this technology. I have also tested on one of the Demo boards to ensure that the layout is not contributing and still getting significant amounts of radiated emissions with the same flyback converter topology any advice or help would be appreciated. Thanks in advance.



Hi, Looking at Radiated emissions of the LTM8067 with near field probe, I appear to be getting significant radiated emissions from the top of the device and out through input and output filter stages causing cross coupling onto nearby circuitry. The frequency is in the HF band around 8-10MHz which some I believe to be harmonics. Do you have any resource, Techniques or advice to improve the radiated emissions on this technology. I have also tested on one of the Demo boards to ensure that the layout is not contributing and still getting significant amounts of radiated emissions with the same flyback converter topology any advice or help would be appreciated. Thanks in advance.
[edited by: NigelPowerDesigner at 12:40 PM (GMT 0) on 29 Nov 2019]
  • For radiated emissions, all I can suggest is placing the module within a noise reducing chamber or possibly placing some sort of noise reducing “wall” between the module and the noise sensitive circuitry…maybe placing the module farther away from the noise sensitive circuitry.

     For conducted emissions, there are things that can be done…adding an input filter, separating GND planes between the module and the noise sensitive circuitry, improved board layout, etc.

     Is the customer sure the noise sensitive circuitry is only affected by the radiated emissions?  Or, is that their educated guess?

     Beyond these generic suggestions, I don’t have any other ideas.

  • Thanks for the response much appreciated, basically I'm the customer\designer trying to resolve the issue and yes I have evaluated the circuitry on our proto board and the LT development board (with no other circuitry), with a near field probe in close proximity to the module package for pre-compliance testing, which is showing in the order of 30dB + of radiated emissions of where I would like to be. I can confirm that the input and output filters are doing what they should be doing. I think that the issue is to do with the rise and fall times of the umodule itself with no access to the gate drive of the flyback topology there is limited scope to reduce the radiated emissions. If there was say a ctrl pin on these type of devices that allowed designers to trade of efficiency with EMI noise would be a good thing.  Sure implementing a screening can and some absorption material does help but like most radiated effects, trying to minimise it in certain areas causes the radiated emissions to appear some where else in the board design in proximity to the device radiating. Unfortunately  the device selection was because of its unique power density within a small surface area because of the design being extremely compact, the advice offered moving the module further away can I ask by what sort of distance ? Thanks in advance.

  • I'm not sure how accurately correlating the results of using a near field probe compared to being done in an EMI chamber. It may also be good to check on an EMI lab.

    There's not much you can do on a micro-module except on the placement of the output caps and the PCB layout.

  • The EMI testing was previously completed in a chamber this is where I identified the radiated emissions problem, to locate the source of the emissions, the investigation used near field probes to sniff around various components and this is where I concluded that the radiated emissions is coming straight from the uModule LTM8067 and also evaluated and confirmed this with the Demo board.

  • Hi ,

    Can you share what radiated emissions standard you are doing the test, board input & output conditions?

  • The standard really is irrelevant the setup is as follows the antenna is approx. 1M away from the EUT, the power input goes through a typical LISN setup then through a screened wall. We are purely powering the EUT on and looking at the radiated noise floor.

  • So this is the only option that is being suggested then for radiated emissions screening chamber and place other electronics further away ?  Finally is it possible for future designs to add a ctrl pin on these type of devices to allow designers to trade of efficiency with EMI noise ? i.e. to incorporate something that allows us to slow the switching rise and fall times ?

  • The answer to your first question to me is yes. We have few modules that are tested to comply to EN55022 Class B standards like the LTM465X but they're not really what you need.

    I definitely agree that adding a feature to improve EMI performance would be great.

  • Thanks all I will now close this thread.