Datasheet

PM8903A Application information
Doc ID 024147 Rev 1 19/33
stability, it should not exceed F
SW
/2π. To achieve a good phase margin, the control loop gain
must cross the 0 dB axis with -20 dB/decade slope.
For example,
Figure 12 shows an asymptotic bode plot of a type III compensation.
Figure 12. Example of type III compensation
The open loop converter singularities are:
The compensation network singularity frequencies are:
F
LC
1
2π LC
OUT
⋅
----------------------------------=
F
ESR
1
2π C
OUT
ESR⋅⋅
--------------------------------------------=
F
Z1
1
2π R
F
C
F
⋅⋅
------------------------------=
F
Z2
1
2π R
FB
R
S
+()C
S
⋅⋅
-----------------------------------------------------=
F
P1
1
2π R
F
C
F
C
P
⋅
C
F
C
P
+
---------------------
⎝⎠
⎛⎞
⋅⋅
--------------------------------------------------=
F
P2
1
2π R
S
C
S
⋅⋅
-------------------------------=