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LMR14020-Q1: Currently LMR14020 operating frequency is 2.2MHz, when customer system is turned off and test noise, will find a 9K peak!

Kygo Cheng
Expert 6830 points
Part Number: LMR14020-Q1
Other Parts Discussed in Thread: LMR14020, TPS54340

Hi Team,

There is currently a noise issue from customer side!

Currently LMR14020 operating frequency is 2.2MHz, when customer system is turned off and test noise, will find a 9K peak!

Do we have any settings that will cause 9K noise? THX 

  • 0
    TI__Expert 8130 points

    Hi Kygo,

    This is a duplicate from yesterday's post.. As I asked in the previous post, conducted emission tests are within the AM band. This peak is at a very low frequency. Are the conducted tests failing?

    Can you provide a schematic? Provide info on the measurement setup?

    Regards,
    Alejandro

  • 0 in reply to iAlejandro
    TI__Expert 6830 points

    Hi iA,

    Sorry for the error information! This issue is not EMI issue! It's " noise  issue" ,THX

    Currently LMR14020 operating frequency is 2.2MHz, when customer system is turned off and test noise, will find a 9K peak!

    Do we have any settings that will cause 9K noise? THX 

    SCH as below

  • 0 in reply to Kygo Cheng
    TI__Expert 8130 points

    Hi Kygo,

    I would like to point out a few confusions:

    1. I'm confused on their switching frequency setting. A value of 9.76kΩ on either device, TPS or LMR, will not give a result of 2.2MHz fsw.
    2. In schematic, UP1, shows a COMP pin. LMR14020 does not have a COMP pin. It has a soft-start (SS) pin.

    Please make sure the appropriate values are placed on the pins for intended behavior.

    Regards,
    Alejandro

  • 0 in reply to iAlejandro
    TI__Expert 6830 points

    Hi iA,

    9K noise can also be measured including ground on all power supplies behind 3.3V.


    1. When customer change the original 2.2MHz operating frequency to 1.9MHz, 9K noise will also become 7.5K noise .
    2. When customer change the operating frequency to 500KHz, the 9K noise interference will disappear.
    >>>It seems that this 9K will follow the working frequency.


    Customer will change TPS54340 to LMR14020 because of EMI problems, because TPS54340 will have 430MHz EMI problems, but if customer change EMI problems will occur again when the operating frequency of LMR14020 is changed to 500K.

  • 0 in reply to Kygo Cheng
    TI__Expert 8130 points

    Hi Kygo,

    Interesting, as you stated, seems as if lowering the fsw improves conducted noise. Did you try getting rid of the high frequency noise on the TPS with some output filtering instead of changing device? Below I have listed a couple of helpful app reports that I would recommend when working with EMI (filters, editing filters, etc.).

    Regards,
    Alejandro