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Conducted emissions using the CCM_CLKO1 with SGTL5000.

Question asked by Josh Barnheiser on Feb 1, 2018
Latest reply on Feb 2, 2018 by Josh Barnheiser

On my custom board I am using the SGTL5000 audio codec and feeding its SYS_MCLK pin with the CCM_CLKO1 signal of the i.MX6. When I test for conducted emissions I get around 27 dBuV at 72 MHz, when the surrounding frequencies are down below 20 dBuV. From turning things off I have found the 24 MHz clock from CCM_CLKO1 to be the problem. I changed the CCM Clock Output Source Register from 0x010e017b to 0x010e00A4 to try to move the radiation to around 27 MHz.

 

Conductive radiation with CCM_CLKO1 at 24 MHz.

Conductive radiation with CCM_CLKO1 at 9 MHz.

 

 

This worked successfully and the radiation didn't even show up at 27 MHz. The SGTL5000 seemed to load fine, but when I tried to play a test file, that had previously worked fine, there was no audio. I am not sure if there is something that needs to be done with the SGTL5000 to get it working with the lower frequency or if there is something else that can be done with the iMX6.

 

Has anyone else experienced emissions with the SGTL5000?

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