L5988DTR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
L5988DTR
STMicroelectronics
L5988DTR Datasheet PDF : 52 Pages
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L5988D
Application information
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 k and 5 k.
2. Choose a gain (R5/R8) in order to have the required bandwidth (BW), that means:
Equation 29
R5 = B-f--L--W-C--- K-1-- R8
where K is the feed forward constant and 1/K is equals to 18.
3. Calculate C5 by placing the zero at 50% of the output filter double pole frequency (fLC):
Equation 30
C5 = --------R-----15-------f--L---C--
4. Calculate C6 by placing the second pole at four times the system bandwidth (BW):
Equation 31
C6 = 2------------R-----5-------C----C5-----5--4--------B----W--------–----1--
5. Set also the fist pole at four times the system bandwidth and also the second zero at
the output filter double pole:
Equation 32
R7 = -4---------f----L--B----C--R----W----8-------–-----1-
C7 = 2------------R-----7--1-----4-------B-----W----
The suggested maximum system bandwidth is equals to the switching frequency divided by
3.5 (FSW/3.5), anyway lower than 120 kHz if the FSW is set higher than 500kHz.
For example with VOUT = 1.2 V, VIN = 12 V, IO = 4 A, L = 4.7 H, COUT = 47 F, the type III
compensation network is:
Equation 33
R8 = 4.7k R6 = 4.7k R7 = 56 R5 = 1.2K C7 = 10nF C5 = 22nF C6 = 1nF
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