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LM5576-Q1: Sw node ring effect

korcan tuna
Prodigy 210 points
Part Number: LM5576-Q1

Dear Team,

LM5576-Q1 is used for buck converter. Sw pin of IC has ring effect as shown in the below picture. This picture is taken at 100 mA load current. The desired load current is maximum 50 mAmps. (Ring effect is worse at 50 mAmps.)  So circuit has to work light load / no load condition. 

Why does this situation occur?

How can I solve this effect at no load/ light load condition? Could you help me about that?

Thanks for support.

  • 0
    TI__Guru 58985 points

    Hello

    This is normal Discontinuous Conduction Mode (DCM) mode operation.

    At light loads the inductor current reaches zero before the next cycle begins.

    At that point the switch node becomes high impedance, since both the HS switch and 

    the diode are off.  The ringing on the switch node at this time is caused by the resonance 

    between the inductor and the stray capacitance on the switch node. 

    The device will regulate and function normally under these conditions.

    Thanks

  • 0 in reply to Frank De Stasi
    Prodigy 210 points

    Shall I decrease ring effect of the SW pin? How can we overcome?

  • +1 in reply to korcan tuna
    TI__Guru 58985 points

    Hello

    I don't think that there is an effective way to remove the DCM ring.

    You may try a series RC snubber across the SW node to ground or from 

    SW node to the Isense node.  The values would need to be experimentally 

    determined.

    Thanks