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TPS54233/Capacitor Selection

Tsukui Yusuke
Guru 21930 points
Other Parts Discussed in Thread: TPS54233
Hi.
 
Please tell me about the following equation.
(TPS54233 data sheet P13 OUTPUT FILTER COMPONENTS ｢Capacitor Selection｣ )
 
"D" Is it Duty?
What do you mean by "D-0.5"?
Please explain equation.
 
Regards,
Yusuke Tsukui.
 
  • 0
    TI__Guru**** 191445 points

    I vaguely remember about this.  The ripple voltage on the output has two primary components, the part due to the ripple current thru the ESR of the output caps and the part due to charging and discharging the capacitance.  They are not in phase with each other.  D is in fact the duty cycle.  For D less than 50%, the effect may be subtractive.  it is a long time since I have seen this derived, but I am pretty sure it is correct.