L6981 datasheet(14/49 Pages) STMICROELECTRONICS

部品番号	L6981

部品情報	38 V, 1.5 A synchronous step-down converter with low quiescent current

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メーカー	STMICROELECTRONICS [STMicroelectronics]

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6.4.2

Low noise mode (LNM)

The low noise mode implements a forced PWM operation over the different loading conditions. The LNM features

a constant switching frequency to minimize the noise in the final application and a constant voltage ripple at fixed

VIN.

The regulator in steady loading condition operates in continuous conduction mode (CCM) over the different

loading conditions.

The triangular shape current ripple (with zero average value) flowing into the output capacitor gives the output

voltage ripple, that depends on the capacitor value and the equivalent resistive component (ESR). Consequently,

the output capacitor has to be selected in order to have a voltage ripple compliant with the application

requirements.

VOUT RIPPLE=ESR∙∆ILMAX+ ∆ILMAX

8∙COUT∙fSW

(3)

Usually the resistive component of the ripple can be neglected if the selected output capacitor is a multi-layer

ceramic capacitor (MLCC).

Figure 13. Low noise mode operation at zero load

L6981

Light-load operation

DS13554 - Rev 1

page 14/49

L6981 データシート(PDF) 14 Page - STMicroelectronics