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| AN1517 Datasheet, PDF (12/30 Pages) STMicroelectronics – Designing with the STEVAL-ISA089V1 high efficiency DC-DC | |||
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Closing the loop
AN1517
Figure 10. Error amplifier equivalent circuit and compensation network
4.2
The poles of this transfer function are (if Cc >> C0+CP):
Equation 3
FP1 = 2-----ï·-----ï°----ï·----1-R----0----ï·-----C----c-
Equation 4
where the zero is defined as:
FP2 = -2----ï·-----ï°----ï·-----R----c----1ï·----ï¨---C----0----+-----C-----p---ï©
Equation 5
FZ1 = 2-----ï·-----ï°----ï·----1-R----c----ï·----C-----c-
FP1 is the low frequency which sets the bandwidth, while the zero FZ1 is usually put near to
the frequency of the double pole of the L-C filter (see Section 4.2: LC filter). FP2 is usually at
a very high frequency.
LC filter
The transfer function of the L-C filter is given by:
Equation 6
ALCï¨sï© = -s---2----ï·----L-----ï·----C-----O----U---T-----ï·----ï¨---E----S----R-----R-+----L-R--O---L-A-O--D--A---ï·-D---ï¨-ï©--1-+----+-s---E--ï·---S-ï¨--E-R----S--ï·--R--C----ï·-O---C-U----TO----Uï·---T-s----ï©ï·----R-----L---O----A---D-----+-----L----ï©---+-----R-----L--O----A----D--
where RLOAD is defined as the ratio between VOUT and IOUT.
12/30
DocID8827 Rev 3
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