PM6681ATR datasheet(35/47 Pages) STMICROELECTRONICS

부품명	PM6681ATR

상세설명	Dual synchronous step-down controller with adjustable LDO

PDF	47 Pages

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제조업체	STMICROELECTRONICS [STMicroelectronics]

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35 / 47 page

PM6681A

Design guidelines

35/47

Figure 39.

Circuitry for output ripple compensation

The stability of the system depends firstly on the output capacitor zero frequency. The

following condition should be satisfied:

Equation 24

where k is a design parameter greater than 3 and Rout is the ESR of the output capacitor. It

determinates the minimum integrator capacitor value CINT:

Equation 25

where gm = 50

µs is the integrator trans conductance.

In order to ensure stability it must be also verified that:

Equation 26

In order to reduce ground noise due to load transient on the other section, it is

recommended to add a resistor RINT and a capacitor Cfilt that, together with CINT, realize a

low pass filter (see Figure 39). The cutoff frequency fCUT must be much greater (10 or more

times) than the switching frequency of the section:

out

Zout

OUT

Zout

INT

⎟

⎠

⎞

⎜

⎝

⎛

−

OUT

Zout

INT

PM6681ATR 데이터시트(PDF) 35 Page - STMicroelectronics