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UCC28950: What is importance of Tmin during startup.

Aniket Bagade
Prodigy 220 points
Part Number: UCC28950

Hii,

I come across this fig in reference document (SLUSA16D) of UCC28950 to drive PSFB converter. According to the manual we must set some minimum duty define by Tmin at the

start of converter, during startup if close loop duty demanded by voltage loop/current loop is less than Tmin then duty will be set to TImin. I want to know what is importance of Tmin duty on converter operation?

What will happen to the converter operation when duty at the start is less than Tmin? How to define value of this Tmin?

Regards

Aniket B.

  • 0
    TI__Guru* 85616 points

    Hello,

    Your inquiry is under review and I will get bet back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 85616 points

    Hello,

    Tmin is the minimum on time that sets the minimum controllable duty cycle (Dmin).  Dmin = Tmin*fsw

    I the controller tries to control below Dmin it will not and will turn off the gate drives until the duty cycle required is greater than Dmin.  This will result in light load bursting.

    This is discussed in the data sheet during startup because you will exhibit missing gate drive pulses during soft start due to this.

    As you pointed out this behavior is discussed in the data sheet.  This was done so when this behavior was observed the design would know that it is normal.

    Regards,