LM5143: How to calculate the Rcs & Ccs by DCR sensing?

Adams Hu

Part Number: LM5143

Tool/software:

In the thead, current sense, TI recommended 100nF to be an initial Ccs for calculating Rcs satisfying the fomular Rcs*Ccs = Lo/Rdcr.

However, Ccs is 197nF in the PMP23404 Schematic

Why to change Ccs from 100nF to 197nF to satisfying the fomular Rcs*Ccs = Lo/Rdcr?

6 months ago

0 Timothy Hegarty 6 months ago

TI__Guru 73842 points

Hi Adams,

100nF and 220nF are standard values for the sense cap. I typically just got with 100nF. The voltage derating for a ceramic capacitor is minimal, as there is no DC voltage. However, it's still good practice to check the actual capacitance with the cap vendor data sheet or online tool, as it may not match the nameplate value.

Regards,

Tim

0 Adams Hu 6 months ago in reply to Timothy Hegarty

Prodigy 10 points

Hi Tim

What if Ccs is in 50nF? What is the criteria of Ccs ranges?

0 Timothy Hegarty 6 months ago in reply to Adams Hu

TI__Guru 73842 points

It's probably okay, but the whole ideal is to maintain low impedance so that the sense voltage can track the inductor current. I would go with >=100nF.

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LM5143: How to calculate the Rcs & Ccs by DCR sensing?