L6911E View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6911E' PDF : 34 Pages View PDF
L6911E
Device description
To choose the other components of the compensation network, the transfer function of the
voltage loop is considered. To simplify the analysis is supposed that R3 << Rd,
where Rd = (R8//R9).
Figure 10. Compensation network definition
|A v|
|R |
R0
fD
|G loo p|
G0
2
fLC
fCE
f2
f1
fEC
fCC
f
f3
f
fc
f
ConverterS ingularity
fLC = 1 / 2π ⋅ LC
fCE = 1 / 2π ⋅ ESR ⋅ COUT
f = 1 / 2π ⋅ ESR ⋅ Cceramic
EC
f = 1 / 2π ⋅ Rceramic ⋅ Cceramic
CC
doublepole
ESRzero
Introduced by
Compensati onNetworkS ingularity
CeramicCap acitor
f1 = 1 / 2π ⋅ R 4 ⋅ C 20
f2 = 1 / 2π ⋅ (R 3 + R 4 ) ⋅ C 20
f3 = 1 / 2π ⋅ R 3 ⋅ C 25
fd = 1 / 2π ⋅ Rd ⋅ C 25
The transfer function may be evaluated neglecting the connection of R8 to PHASE because,
as will see later, this connection is important only at low frequencies. So R4 is considered
connected to VOUT. Under this assumption, the voltage loop has the following transfer
function:
Equation 17
Gloop(s)
=
Av(s) ⋅ R(s)
=
Av(
s)
⋅
Z-----f--(--s---)-
Zi(s)
where
Av(s)
=
----V----i--n-----
∆V o s c
⋅
-----------Z----C----(--s----)----------
ZC(s) + ZL(s)
Where ZC(s) and ZL(s) are the output capacitor and inductor impedance respectively.
The expression of ZI(s) may be simplified as follow:
21/34
Share Link: 
