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CSD19533Q5 Jitter issue

Other Parts Discussed in Thread: LM5117

Dear Sir 

We use LM5117 with CSD19533Q5 and HAT2244WP for 48Vin to 12Vout / 5A

When use CSD19533Q5 ,the jitter will be bigger than using HAT2244WP ,Do you know which MOSFET parameter effect the jitter performance

Qg ?? or CISS ??  

Waveform 

  • By jitter, do you mean ringing? Yes our 100V FETs do tend to ring. In part this is due to the fact that they have very low Qg and turn on so fast. The faster the turn on/off, the greater the ringing.
  • Dear Brett

    Thanks for your reply 

    I mean the falling edge of pulse 

    The schematic is the same ,but the jitter is not better than HAT2244

    Do you have any idea?

  • Here is the response from our applications team:

    FETs don’t have any brain and any control mechanisms to decide the turn OFF event and the falling edge of the Switch-node signal.

    What you drive is what you get.

    Noise injection in the Control loops ( for example Vout Feedback sense into the Controller input) for D-cap or Voltage mode controllers and Current signal shape and Signal-to-Noise Ratio on Current mode Controllers dictate your turn-off edge.

    In general the logic is simple: if you have Jitter it means your Converter loop is NOT stable. Get back to the Bode plots , Pole/zeroes Compensation and Make it stable.

    Let he FET alone: it’s NOT responsible for your Poor Loop Compensation.