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TPS40428: Total Capacitance vs. Local Capacitance consideration for Loop Compensation

Hayden_Hast
Intellectual 1515 points
Part Number: TPS40428

Hi Team,

I'm working on designing multiple instances of the TPS40428 + TI Power Stage regulators into my system and had a question regarding loop compensation. I have selected the appropriate compensation components and output capacitance for my regulator to ensure stability and good transient response (Fco > 1/10 Fsw, PM > 55% & GM >10db).

However, the IC that I'm supplying the load to has a significant number of input caps (let's say between 100uF and 500uF) and is located a significant amount of distance away from my regulator. My question is... Do I need to factor the load IC input capacitance into my loop calculations even if the load is physically located a distance away from the regulator? Also, what measure do I need to take the added trace inductance into consideration as well?

I was hoping we had some good collateral on this, but I couldn't find any. 

Thanks for your help,

Hayden

  • 0
    TI__Expert 5965 points

    Hi Hayden,

    You will need to account for the capacitors near the IC load. Since they are further away from other output capacitors, usually there is inductance/resistance between the capacitors at IC load and the capacitors near inductor output. This will cause extra poles and may reduce your phase margin. The location of the poles depends on the capacitance value and parasitic inductance/resistance which is determined by the board design. But if you measure your stability (bode plot) with the capacitors near IC load and pass phase/gain margin criteria with reasonable Fco you should be in good shape.

    Regards,

    Weidong

  • 0 in reply to Weidong Zhu
    TI__Intellectual 1515 points
    Weidong,

    Thanks for the quick response, this confirms our understanding.

    Regards,
    Hayden