Datasheet
DocID17928 Rev 5 11/29
ST1S40 Functional description
29
Figure 5. Small signal model for the error amplifier
R
C
and C
C
introduce a pole and a zero in the open loop gain. C
P
does not significantly affect
system stability and can be neglected.
So G
EA
(s) results:
Equation 8
where G
EA
= G
m
· R
o
The poles of this transfer function are (if C
c
>> C
0
+C
P
):
Equation 9
Equation 10
whereas the zero is defined as:
Equation 11
The embedded compensation network is R
C
= 70 k, C
C
= 195 pF while C
P
and C
O
can be
considered as negligible. The error amplifier output resistance is 240 M
so the relevant
singularities are:
Equation 12
&R5R
&F
5F
&S
*P9G
9
)%
9
5()
9G
G
EA
s
G
EA0
1s+ R
c
C
c
s
2
R
0
C
0
C
p
+R
c
C
c
sR
0
C
c
R
0
C
0
C
p
+R
c
C
c
++1++
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------=
f
P LF
1
2 R
0
C
c
--------------------------------- -=
f
P HF
1
2 R
c
C
0
C
p
+
----------------------------------------------------=
f
Z
1
2 R
c
C
c
---------------------------------=
f
Z
11 6 kHz= f
P LF
34 Hz=