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Output Capacitance consideration in Buck compensation equations....

malli arjun1
Intellectual 610 points
Other Parts Discussed in Thread: TPS54620

Hi,

When calculating compensation values for Buck converter(TPS54620), i found few equations,

For TPS54620,

we have Output Bulk capacitors 4, 100uf's and lots of decoupling capacitors(0.1uF or 0.01uF) near to ASIC on same rail.

Here Cout means whether we need to consider complete capacitance or only Capacitance proximity to PS54620 output node alone.

another case,

In case we have a ferrite bead and then few output capacitors, whether we need to consider Capacitors after Ferrite bead also.

  • 0
    TI__Guru**** 191445 points

    In general you can use the local capacitance for those equations.  You may want to use some engineering judgement as to how much additional to add.  Probably a more important effect is dc-bias.  You need to derate the typical value based on the dc output voltage relative to the rated voltage.  You may be surprised at how much the capacitance is decreased as the dc voltage increases.  Also. I almost never use those design equations.  They are first order approximations that will get you a starting point.  I prefer to use pspice modeling when I design compensation circuits.  That way I can include remote decoupling capacitors, the effect of ferrite beads, etc.