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LT3763 has ringing TG FET gate, will not regulate current

Category: Hardware
Product Number: LT3763

Creating a LED CC control based on eval board.  Eval board works with Rs changed. 

Some parts had to be substituted, one of which is the FET, using BSC117N08NS5ATMA1.

Board shows current is not regulated to 3A, and the Top gate has ringing.  BG does not wiggle.

TG  

Is the FET used incompatible? Do the values on the VC pin need to be adjusted?

Parents
  • Hi,

    what point shows your scope picture?
    Is it the hot side of your inductor?
    What I see in your picture is that the converter is not in continous mode.
    That is, when BG transistor turns off TG is not turned on immediately, becaus the load current is to small or the inductance value
    is to small or your switching frequency is to low.
    In this discontinous mode the ringing is normal as your inductor together with the mosfets capacitances makes a resonant circuit.

Reply
  • Hi,

    what point shows your scope picture?
    Is it the hot side of your inductor?
    What I see in your picture is that the converter is not in continous mode.
    That is, when BG transistor turns off TG is not turned on immediately, becaus the load current is to small or the inductance value
    is to small or your switching frequency is to low.
    In this discontinous mode the ringing is normal as your inductor together with the mosfets capacitances makes a resonant circuit.

Children