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Ground strategy for LM22676

Marcin Tesmer
Prodigy 40 points
Other Parts Discussed in Thread: LM22676

Good afternoon,


I would like ask for a second opinion regard LM22676 connection to the common ground where regulator itself is a part of bigger circuitry not a stand alone board. I attached a sample PCB layout in two cases. One when regulator was placed on separate DC round plane another where regulator is directly connected to the common ground plane. The PCB itself contain all necessary components to drive and control TFT LCD and CAN interface. Knowing advantages and disadvantages I still trying to decide which way is better.

Best Regards,

Marcin

for TI.zip
  • 0
    TI__Genius 16025 points

    Hi Marcin,

    We've received your query and will get back to you shortly.

    Thanks,

    Anston

  • 0 in reply to Anston Lobo
    TI__Genius 16025 points

    Hi Marcin,

    Our recommendation is for the separate DC grounding method. Here's why, the function of any regulator stage be it linear or switching is to provide a low output noise voltage. The lowest output noise voltage appears across the output capacitor of the regulator.  In the case of a non isolated switching regulator, there are several other separate connections on the ground net. Your application has the unique configuration that allows configuring this net so that discontinuous diode, switch and input capacitor currents are segregated from the system ground. This keeps the switching regulator ground currents from migrating into the rest of the system. We do suggest adding bypass ceramic capacitors in addition to the large electrolytic that is present on Cout C42.

    seprate_DCground.gif is the preferred layout.

    Thanks,

    Anston

  • 0 in reply to Anston Lobo
    Prodigy 40 points

    Hi Anston,

    Thank You for a valuable feedback. My only concern to the recommended solution is DC plane on top layer. It looks broken around VR1 (please check attached image). I think I should keep ground space on top to the minimum and use inner layer 1 ( layer closer to the top)  as main DC ground and possibly add another ground plane on the bottom layer for better heat dissipation from regulator and diode . What do you think about my idea?

    Thanks,
    Marcin

    DCground.zip
  • 0 in reply to Marcin Tesmer
    TI__Genius 16025 points

    Hi Marcin,

    We think you should proceed with DCground_ver2.gif or Version 2. It will provide better heat dissipation as you pointed out and this is a very good idea.

    A good aspect of your component placement is that the discontinuous current of C40, IC ground, and catch diode are as short as possible and not directly attached to your global ground plane but instead segregated into their own area. 

    Thanks,

    Anston

  • 0 in reply to Anston Lobo
    Prodigy 40 points

    Hi Anston,


    Once more thank you for Your help. I'll follow your advices and proceed further with version two.

    Best Regards,

    Marcin