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LM5164: LM5164 RINGING issue

sung jin park
Prodigy 130 points
Part Number: LM5164
Other Parts Discussed in Thread: LM5163

TINA-010208 as a REFERENCE circuit diagram
I designed the circuit diagram of LM5163 and applied LM5164 for the actual parts.
The LM5164 is currently experiencing a RINGING phenomenon.
What debugging should I do to fix the RINGING issue?

image.png

  • 0
    TI__Genius 9602 points

    Hi Sung,

    What kind of ringing you are talking about-can you please elaborate more/show waveforms? What are the operating conditions Vin, Io?? If the load current is very less, the device will enter to DCM and you can see ringing in SW node waveform after inductor current becomes 0. 

    Regards

    Arpita

  • 0 in reply to ARPITA NATH
    Prodigy 130 points

    When the load current is below what A does it enter the DCM?

  • 0 in reply to sung jin park
    TI__Genius 9602 points

    Hi Sung,

    At what current you are seeing the ringing? To confirm that it is due to DCM operation, can you please provide above requested waveforms?

    The output current at the boundary of CCM and DCM is calculated as mentioned in datasheet

    The peak-to-peak inductor current ripple (del_iL) depends on operating conditions and circuit parameters. To calculate this, please find datasheet eq

    Regards

    Arpita

  • 0 in reply to ARPITA NATH
    Prodigy 50 points

        

        

    Hi, this is a waveforms of the ringing issue. 

    When the ringing noise occurs, I can clearly hear the noise switching between a high-pitch tone and a low-pitch tone in a periodic manner.
    The first and second images were captured when the high-pitch noise was heard.
    The third and fourth images were also captured during the high-pitch noise condition.

    For reference, the power supply input current repeatedly cycles between 6–7 mA and then suddenly jumps to around 90 mA, and this pattern keeps repeating.

  • 0 in reply to yurin kwon
    TI__Genius 9602 points

    Hi Yurin,

    Can you label waveforms? Also mention test conditions (vin, Load current etc)

  • 0 in reply to ARPITA NATH
    Prodigy 50 points

    CH1 is Vin, CH2 is the node before L2, and CH3 is the node after L2.


    Test condition: Vin = 48V (power supply), no external load. 
    (However, as mentioned above, the board internally draws a fluctuating current between 6–7 mA and up to 90 mA, even under no-load conditions.)

  • 0 in reply to yurin kwon
    TI__Genius 9602 points

    Hi Yurin,

    What was the load current for first two images? From the SW node waveform, It looks like the load current was higher (CCM) for first two images. Can you please mention correct test conditions?

  • 0 in reply to ARPITA NATH
    Prodigy 50 points

    The load current was not changed during the tests.
    The bench power supply was set to 48V, 1A, CV mode, and remained fixed.

    As I mentioned earlier, the board (or the DC/DC converter) periodically switches between the conditions shown in images 1–2 and images 3–4.
    The audible noise also alternates between a high-pitch tone and a low-pitch tone.

    When the high-pitch noise occurs, the input current suddenly increases to about 90 mA.
    When the low-pitch noise occurs, the input current drops to around 6–7 mA.

  • 0 in reply to yurin kwon
    TI__Genius 9602 points

    Hi Yurin,

    In 1st pair of images- SW node waveforms look like CCM mode, Operating frequency ~100kHz

    In 2nd pair of images- SW node waveforms look like DCM mode, skip frequency <10kHZ.

    It shows load current was reduced in second case. Please double check thoroughly if some periodically /pulsating load is present. 

    Please probe load current. I think as your load current is changing, the input current drawn is changed.