L5983 datasheet(19/37 Pages) STMICROELECTRONICS

Teilenummer	L5983

Bauteilbeschribung	1.5 A step-down switching regulator

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Hersteller	STMICROELECTRONICS [STMicroelectronics]

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Application information

L5983

19/37

Figure 10.

Type III compensation network

In Figure 11 the Bode diagram of the PWM and LC filter transfer function (GPW0 · GLC(f))

and the open loop gain (GLOOP(f)=GPW0 · GLC(f) · GTYPEIII(f)) are drawn.

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 1 k and 5 k.

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):

----------

---- R

⋅⋅

L5983 Datenblatt(PDF) 19 Page - STMicroelectronics