L5985TR datasheet(23/37 Pages) STMICROELECTRONICS

Part #	L5985TR

Description	2 A step-down switching regulator

PDF	37 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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L5985

Application information

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Figure 13.

Type II compensation network

The singularities of the network are:

In Figure 14 the Bode diagram of the PWM and LC filter transfer function (GPW0 · GLC(f))

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

Figure 14.

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, in order to have values of C4 and

C5 not comparable with parasitic capacitance of the board.

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

π R

⋅⋅

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π R

⋅

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⋅⋅

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L5985TR Datasheet(PDF) 23 Page - STMicroelectronics