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LMR36006-Q1: EMC issue

Amber Si
Intellectual 2165 points
Part Number: LMR36006-Q1
Other Parts Discussed in Thread: LMR36506, LMR36006

Tool/software:

Hi  team,

Merry Charismas!

My customer use LMR36006AQRNXRQ1 in auto BMS MCU supply, VIN is 24V, VOUT is 5V/60mA. DCDC fail on EMI CE current method and RE (standard :CISPR25 class 4), test result :(CE margin on FM frequency is only 1dB；RE on MW frequency is 2dB above standard)  and what they try to do for this result as attachment

They try to change to LMR36006FSCQRNXRQ1 (2.1MHz with SPREAD SPECTRUM), DCDC successfully pass CE(Margin is 6dB) and RE, I also attach what they do for LMR36006FSCQRNXRQ1

But the issue is LMR36006FSCQRNXRQ1 efficiency is too low< 30% at light load 60mA as FPWM, cause thermal issue.

LM36006.docx

Support need:

  1. For LMR36006AQRNXRQ1, what else they can do for EMC pass? I confuse EVM test report show 400kHz without SPREAD SPECTRUM can also pass EMI.
  2. If they change to LMR36006FSCQRNXRQ1, what they can do to improve  efficiency, Now inductor is 10uH, I think there is no solution to further improve as datasheet show the same level.
  3. What other device we can recommend to customer for both good EMC and efficiency(60V Max input, 5V output, <1A is enough)?

BR

Amber

  • 0
    TI__Mastermind 31315 points

    Hi Amber,

    Usually for CE test, the main suspect is in the input filter. With a LC input filter, the easiest way is to add a parallel damping network (aluminum electrolytic capacitor) after the inductor. It looks like you were trying to implement a two-stage filter, I would first recommend trying it with a single-stage with damping network (as shown in the app note), and then add a second inductor with its own damping network if you need additional margin. 

    To pass RE test, usually it is a function of layout, how many layers is the board? Typically our EVM is implemented on a 4 layer board with two ground layers in between, so that can be a difference in your design,  

    https://www.ti.com/lit/an/snva538/snva538.pdf?ts=1735605995024&ref_url=https%253A%252F%252Fwww.google.com%252F

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    TI__Intellectual 2165 points

    Hi 

    How about LMR36506? I found it is both good EMC and efficiency, I recommend customer to try this device. Do you have insight if it will be easier to pass RE and CE?

    BR

    Amber

  • 0 in reply to Amber Si
    TI__Mastermind 31315 points

    Hi Amber,

    LMR36506 can also work, but I suspect a large portion of this will be due to your input filter, as seen in both the LMR36506 and LMR36006. Honestly, based off of the test result, it may be easier to pass with the LMR36006 from the EMI waveform and due to the additional VIN pin that will help with RE, but it will depend on application to application

    Thanks,

    Richard