# What might this term (N sub C) be, calculating ripple current for a buck converter output capacitor?

I'm reading through the datasheet for TI's TPS54302 step-down converter, and determining values for support components.

There is a calculation to determine ripple current for the output capacitor which is:

$$I_{COUT(RMS)} = \frac{1}{\sqrt12} \times \left( \frac{V_{OUT}\times(V_{IN(MAX)}-V_{OUT})} {V_{IN(MAX)} \times L_{OUT} \times f_{SW} \times N_C} \right)$$ (Where $$\L_{OUT}\$$ is the inductor value (H), $$\f_{SW}\$$ is the switching frequency (Hz).)

I'm not sure what the term $$\N_C\$$ is meant to be.

Looking around online, other formulas omit this. For example, in this document by Rohm titled Capacitor Calculation for Buck Converter IC, page 4 has the formula:

$$I_{CO} = \frac{1}{\sqrt12} \times \left( \frac{V_{OUT}(V_{IN(MAX)}-V_{OUT})} {L \times f_{SW} \times V_{IN(MAX)}} \right)$$

Either I am ignorant of what $$\N_C\$$ is in this context (the datasheet doesn't clarify); the term is optional depending on application; or TI has a mistake in the datasheet.

What is $$\N_C\$$ in this case?

• The data sheet doesn't say that $N_C$ is the number of output capacitors, but the schematic has two, and the text says that equation 15 gives the equation "for each capacitor". Bad technical writing style, there TI, to not name all your variables! Jan 8, 2019 at 1:04