L5981 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

L5981

1A step-down switching regulator

STMicroelectronics 

Application informations

L5981

minimize the dc error on regulated output voltage; finally to place other poles far away the

zero dB frequency.

In Figure 10 the type III compensation network is shown. This network introduces two zeros

(fZ1, fZ2) and three poles (fP0, fP1, fP2). They expression are:

Equation 16

Equation 17

fZ1 = 2----π-----⋅---C-----3----⋅--1-(--R-----1----+-----R----3----),

fZ2 = 2----π-----⋅---R--1---4----⋅---C----4-

fP0 = 0,

fP1

=

--------------1--------------- ,

2π ⋅ R3 ⋅ C3

fP2

=

---------------------1----------------------

2π

⋅

R4

⋅

-C-----4----⋅---C-----5--

C4 + C5

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.

19/37

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