Datasheet

ADP2323 Data Sheet
Rev. A | Page 22 of 32
R
ESR
is the equivalent series resistance of the output capacitor.
The ADP2323 uses a transconductance amplifier for the error
amplifier to compensate the system. Figure 47 shows the
simplified peak current-mode control small signal circuit.
R
ESR
R
+
–
g
m
R
C
C
CP
C
OUT
C
C
R
TOP
R
BOT
–
+
A
VI
V
OUT
V
COMP
V
OUT
09357-049
Figure 47. Simplified Peak Current-Mode Control Small Signal Circuit
The compensation components, R
C
and C
C
, contribute a zero,
and the optional C
CP
and R
C
contribute an optional pole.
The closed-loop transfer equation is as follows:
)(
1
1
)( sG
s
CC
CCR
s
sCR
CC
g
RR
R
sT
vd
CPC
CPCC
CC
CPC
m
TOPBOT
BOT
V
×








×
+
××
+×
××+
×
+
−
×
+
=
The following design guideline shows how to select the
compensation components, R
C
, C
C
, and C
CP
, for ceramic output
capacitor applications.
1. Determine the cross frequency (f
C
). Generally, the f
C
is
between f
SW
/12 and f
SW
/6.
2. R
C
can be calculated using the following equation:
VI
m
C
OUTOUT
C
Ag
fCV
R
××
×××π×
=
V6.0
2
3. Place the compensation zero at the domain pole (f
P
).
C
C
can be determined by
( )
C
OUT
ESR
C
R
CRR
C
×+
=
4. C
CP
is optional. It can be used to cancel the zero caused by
the ESR of the output capacitor.
C
OUT
ESR
CP
R
CR
C
×
=
The ADP2323 has a 10 pF capacitor internally at the
COMPx pin; therefore, if C
CP
is smaller than 10 pF, no
external capacitor is needed.