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LM5105: Half-bridge control signal noises

Oskar Alonso
Prodigy 50 points
Part Number: LM5105

Hi,

I'm having a problem with LM5105. I'm having problems with noise in IN signal and in 3V3. I'm not finding the problem why this noise commutation is appearing in this signals. I don't know if its problem of PCB design or schmetic design. I attach schematic design in order to know if it is possible to reduce this noise because of anything wrong in it. I have already tried with distint type of snubbers but this doesn't change the behaviour of this signals.

Schematic

HS

3V3

IN

I have tried with this two kind of MOSFETs and the result is very similar. FDT86244 and IRFL014

Thanks

  • 0
    Prodigy 50 points

    Commutation frequency is 200 kHz

  • 0 in reply to Oskar Alonso
    TI__Genius 13650 points

    Hi Oskar,

    Welcome to E2E!

    Our expert is reviewing the information provided and will get back to you promptly.

    Thanks for your patience.

    Best regards,

    Andy Robles

  • 0 in reply to Andy Robles
    TI__Genius 13445 points

    Oskar,

    I have looked at your schematic and there several things you may need to address:

    1. 45V on VDD is exceeding the recommended operating conditions, please ensure that this is within 8 to 14V.

    2. VDD also requires its own local decoupling capacitors sized 10xC_hb_hs.

    2. Depending on your Fsw and MOSFET gate charge, HB-HS cap might be too large. 100nF is generally OK.

    3. EN pin should also have its local decoupling cap <1000pF to filter out noise.

    I suggest you review "8.2 Typical Application" of the d/s and let us know if you're still having issues once you have implemented those changes.

    Meanwhile, I will mark this thread as "resolved".

    Regards,

    -Mamadou

  • 0 in reply to Mamadou Diallo
    Prodigy 50 points

    Sorry, that picture does not reflect the last state of my circuit. In next picture you can see the actual state of the circuit.

    I hav also tried with Cboot 470nF but the behaviour of the signals is very similar. The capacitor on the Enable pin does not improve the performance of the IC.

    Thanks for the reply.

  • 0 in reply to Oskar Alonso
    TI__Genius 13445 points

    Oskar,

    Thanks for the updated schematic, we will review and get back to you.

    Thanks for your patience.

    -Mamadou

  • 0 in reply to Mamadou Diallo
    TI__Mastermind 21575 points

    Hello Oskar,

    Thank you for the updated schematic. To help with noise reduction on the EN and IN pins, it will help to have an R/C filter instead of just the capacitor on the device pin. Make sure the capacitors are placed close to the device pins which has likely already been suggested. For the resistor, it is better to have close to the IC pins you want to filter but not as critical. Try a resistance that results in a 10-20ns time constant as a start and you can increase the R or C if you want to achieve more noise reduction.

    Confirm if this addresses your questions or you can post another question on this thread.

    Regards,

  • 0 in reply to Richard Herring
    Prodigy 50 points

    Thanks, Mamadou.

    I have tried your solution but I'm not able to reduce that noises, in fact, the best behaviour is without any filter in that pins. I think it could be a routing problem. I have follewed the layout guideness of the datasheet but it doesn't seem to be enough. Is there any development board or any example layout I could take as an example?

  • 0 in reply to Oskar Alonso
    TI__Mastermind 21575 points

    Hello Oskar,

    It is possible that there is ground bounce from the driver ground reference and the controller ground which is causing the issue. Also you need to be careful in connecting the scope probes to avoid noise pickup from the test setup. Connect the scope probes as close as possible to the IC pins with a short ground connection. using the wire spring connection to the scope ground ring is the best connection.

    We do not have a dedicated EVM for this device. Is it possible to share your layout so we can review? If this is information you do not want public, you can friend us for a private information exchange.

    Try confirming the scope connections for short connections, avoid grounding multiple scope probes on different ground points. Examining the waveforms with only one probe and signal also helps to see if there is noise from the scope setup,

    Confirm if this addresses your questions, or you can post additional questions on this thread.

    Regards,