L5985 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L5985' PDF : 36 Pages View PDF
L5985
Figure 11. Open loop gain: module Bode diagram
Application informations
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:
Equation 21
R3
=
-----------R----1----------- ,
4-----⋅---B-----W---- – 1
fLC
C3
=
-------------------1---------------------
2π ⋅ R3 ⋅ 4 ⋅ BW
20/36
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