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Load capacitance estimation for compensation of switching power supplies

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steinar96

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I'm calculating a compensation network for power supplies based on the LM20323MH from TI.

http://www.ti.com/lit/ds/symlink/lm20323.pdf

I have slight doubts about correct estimation of output capacitance to use in the calculation. The board is a cpu motherboard (i.mx6q quad core, 1.4 Ghz) so there is a lot of distributed capacitance around the board, bigger then the output caps for the switcher itself.

Should i account for all the capacitance across the board or just the capacitors close to and associated to the power supply. I do not have much insight at the moment into how the capacitance separated some distance away plays into the stability of the switchers.

So the question is, should i account for all capacitance seen by the output of the switchers or just the capacitors close to and associated with the switcher.

Intuition tells me that i should account for the total board capacitance since there will likely be a low impedance connection to the distributed capacitors via power planes. But i'm not 100% sure.

Thank you.
 

BradtheRad

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Do you know how much current will be going back and forth through the output (or smoothing) capacitor?

Do you know how much current ripple there will be in your coil? (Continuous conduction mode produces less ripple current than discontinuous mode does.)

If these figures are high, then that will mean a high amount of current flowing through traces on your pcb.
 

steinar96

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Do you know how much current will be going back and forth through the output (or smoothing) capacitor?

Do you know how much current ripple there will be in your coil? (Continuous conduction mode produces less ripple current than discontinuous mode does.)

If these figures are high, then that will mean a high amount of current flowing through traces on your pcb.
This is not related to my question, my question is related to the calculation of the feedback network. Whether to use the capacitance of the capacitors close to the switcher or to use the combined capacitance of all the capacitors connected to the power network, even those far away on the board.
 

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