L5980 データシートの表示（PDF） - STMicroelectronics

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L5980

0.7 A step-down switching regulator

STMicroelectronics 

Application information

Equation 17

fP0 = 0,

fP1

=

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

2π ⋅ R3 ⋅ C3

fP2

=

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

2

π

⋅

R4

⋅

-C-----4----⋅---C-----5--

C4 + C5

Figure 10. Type III compensation network

L5980

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:

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

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

19/37

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