L5985 查看數據表（PDF） - STMicroelectronics

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产品描述 (功能)

生产厂家

L5985

2A step-down switching regulator

STMicroelectronics 

L5985

5.4.1

Application informations

Type III compensation network

The methodology to stabilize the loop consists of placing two zeros to compensate the effect

of the LC double pole, so increasing phase margin; then to place one pole in the origin to

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

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

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

Equation 17

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.

19/36

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