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UCC28950: UCC28950 SR MOS

user6004348
Intellectual 390 points
Part Number: UCC28950

HI SIR 

If I want SR gate to always be turned on, How do i setting

I try to adjust pin 12( DCM) , but it can’t achieve what I want

TKS

  • 0
    TI__Mastermind 40580 points

    Hello User6004348,

    Thank you for your interest in the UCC28950 PSFB controller. 

    The design of this controller will not allow either SR gate to be always ON.  There must be some off time to allow for voltage to ramp up current in the output inductor.  The DCM pin allows for setting the threshold for both SR gates to be always OFF, but not for both to be always ON. 

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Intellectual 390 points

    HI SIR

    Sorry may be my description is wrong

    I mean that i want Dynamic SR ON at 0.1A~full load(12V/67A)

    Is this possible? If it can, are there other things to note

    TKS

  • 0 in reply to user6004348
    TI__Mastermind 40580 points

    Hello TKS,

    I believe that it is not possible to keep the SR FETs on for a load level down to 0.1A out of 67A, which is 0.15% of full load. The operation will surely be discontinuous, so the DCM must be used, but the setting at such a low current will have too much variance to achieve repeatability from one unit to the next.

    You may be able to dial in such a sensitive setting with a trim-pot for one unit, but the next unit will have a different threshold and each unit's setting can drift with temperature and aging. The recommended range for DCM (see Table 6.3 in the datasheet) has a minimum level of about 5%.
    Perhaps you can run at a lower level if you allow a wide load variability between units, but I think it is not possible at 0.15% of full load.

    Regards,
    Urlrch