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UCC28740: Start up time calculation

Ryoma Ohashi
Expert 4955 points
Part Number: UCC28740
Other Parts Discussed in Thread: UCC28742

Tool/software:

Hi team,

Will the worst case start up time be calculated with below formula?

t_st(worst case)=Cvdd*23V/100uA          (If Cvdd=10uF, then tst(worst case)=10u*23V/100u=2.3s)

If we want to make the start up time shorter, the option is to make Cvdd smaller or use UCC28742 and use small Rst?

Regards
Ohashi

  • +1
    TI__Genius 12785 points

    Yes, that would be the worst worst case. In reality, the charge current is 250uA. If you use smaller cap (our ref designs typically use < 5uF), it will take 200mS for IC to start switching once input is applied.

    If faster start up is needed, you can reduce Cvdd or use UCC28742 with smaller Rst.