L5980 datasheet(20/37 Pages) STMICROELECTRONICS

No. de pieza	L5980

Descripción Electrónicos	0.7A step-down switching regulator

PDF	37 Pages

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Fabricante Electrónico	STMICROELECTRONICS [STMicroelectronics]

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20 / 37 page

Application informations

L5980

20/37

Figure 11.

Open loop gain: module Bode diagram

The guidelines for positioning the poles and the zeroes and for calculating the component

values can be summarized as follow:

Choose a value for R1, usually between 1kΩ and 5kΩ.

Choose a gain (R4/R1) in order to have the required bandwidth (BW), that means:

Equation 18

where K is the feed forward constant and 1/K is equals to 9.

Calculate C4 by placing the zero at 50% of the output filter double pole frequency (fLC):

Equation 19

Calculate C5 by placing the second pole at four times the system bandwidth (BW):

Equation 20

Set also the first pole at four times the system bandwidth and also the second zero at

the output filter double pole:

----------

---- R

⋅⋅

π R

⋅⋅

---------------------------

π R

4BW

⋅

–

⋅⋅⋅

--------------------------------------------------------------

L5980 Datasheet(PDF) 20 Page - STMicroelectronics