About Kinetis K60, EMC and EMI's

[santiago]

Hi all,

At my company we decided to change our project microcontroller (Silicon Labs 8051F120) due to the high level of emissions produced and that makes us practically impossible to obtain CE certification for Class B domestic environment.

Since we had already decided to migrate to a 32-bit microcontroller, we are evaluating the possibility of using the Freescale K60 or K61 for its RTOS (MQX) and free development tools (CodeWarrior).

However, to measure the level of emissions from its evaluation board TWR-K60N512 we found that also produces some peaks up to 10 dB higher than required, and the EMC radiated emissions declared in its datasheet are relatively high (Radiated emissions voltage, band 3 150–500 MHz = 29 dBμV) when the limits for this band are between 30 and 37 dBμV/m.

It is possible that the evaluation board has not been designed with a view to minimizing the EMI's, but it's too scary to fall into the hands of a very noisy microcontroller.

Does anyone have experience working with this microcontroller and has passed the certification of EMC according to EN 50491-5-2:2010?

Best regards and thank you very much

Santiago

[john_suchyta]

Hello Santiago,

The EN standard is a system level specification that applies to the entire system. The radiated emissions values given in the datasheet are measured using an IEC standard that applies to ICs and gives relative numbers for general comparison of devices. Emissions on signal traces coming from the device are much more important in overall systems emissions than the device emissions. The device emissions (IEC 61967-1) are near-field measurements taken at 45 mm from the device; what they will be in the far field (antenna measurements 3-10 meters from the board under test) will be quite bit different. Keys to low emissions are board layout to reduce unintentional antennas, taking care of power supply bypass close to the device, reducing rise/fall times with programmable drive strengths and slew rates, proper cabling connections and bypass, etc.

Regarding the TWR board FCC compliance: the boards are tested for emissions using typical demo code and perhaps one USB cable. Adding cables, changing output drive strengths/slew rates and running higher frequencies can affect the emissions performance of the system.

It would be good to have comments from anyone in the Community who has success or failure with EN50491-5-2:2010 [EMC requirements for Home and Building Electronic Systems (HBES) and Building Automation and Control Systems (BACS)].

Hope this helps in the meantime.

Regards,

John Suchyta

[vicentegomez]

Hi also you can check our recommendation about the EMC on the application note AN4747 EMC Design Tips for Kinetis L Family

http://www.freescale.com/files/32bit/doc/app_note/AN4747.pdf

Also the following application notes may help you.

AN1050

Designing for Electromagnetic Compatibility (EMC)

with HCMOS Microcontrollers

http://www.freescale.com/files/microcontrollers/doc/app_note/AN1050.pdf

AN2764    Improving the Transient Immunity

Performance of Microcontroller-Based Applications

http://www.freescale.com/files/microcontrollers/doc/app_note/AN2764.pdf