L5981 查看數據表（PDF） - STMicroelectronics

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L5981

1A step-down switching regulator

STMicroelectronics 

Application informations

Figure 11. Open loop gain: module Bode diagram

L5981

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 1k and 5k.

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

Equation 18

R4

=

B-----W----

fLC

⋅

-1--

K

⋅

R1

where K is the feed forward constant and 1/K is equals to 9.

3. Calculate C4 by placing the zero at 50% of the output filter double pole frequency (fLC):

Equation 19

C4

=

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

π ⋅ R4 ⋅ fLC

4. Calculate C5 by placing the second pole at four times the system bandwidth (BW):

Equation 20

C5 = 2----π-----⋅---R-----4----⋅---C----C4----⋅-4--4-----⋅---B----W--------–----1--

5. Set also the first pole at four times the system bandwidth and also the second zero at

the output filter double pole:

20/37

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