# I_rms of input capacitor to buck controller. What is it?

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#### king.oslo

##### New Member
Hello there,

The MAX8792 datasheet (http://www.electro-tech-online.com/custompdfs/2012/01/MAX8792-1.pdf) depict a C[SUB]in[/SUB]. It is placed on the input to the high-side switching MOSFET and the T[SUB]on[/SUB]-pin.

The datasheet says:

The input capacitor must meet the ripple current requirement (I[SUB]RMS[/SUB]) imposed by the switching currents. The I[SUB]RMS[/SUB] requirements may be determined by the following equation:

[LATEX]I_R_M_S = (\frac{I_L_O_A_D}{V_I_N})\sqrt{V_o_u_t(V_i_n-V_o_u_t)}[/LATEX]
In layman's terms, what is the I[SUB]RMS[/SUB] referred to here? Is this the ripple current rating the capacitor must have for longlivity? Is this some kind of current requirement to for proper output current capability?

Kind regards,
Marius

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