L5987 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L5987' PDF : 40 Pages View PDF
Application information
Figure 11. Type III compensation network
L5987
In Figure 12 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 12. 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 follows:
1. Choose a value for R1, usually between 1 k and 5 k.
2. Choose a gain (R4/R1) in order to have the required bandwidth (BW), that means:
Equation 22
R4 = B-----W-f--L--C-----K-- R1
where K is the feedforward constant and 1 / K is equal to 9.
22/40
DocID14972 Rev 4
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