Datasheet

Data Sheet ADP2380
Rev. 0 | Page 19 of 28
Use the following design guidelines to select the R
C
, C
C
, and C
CP
compensation components:
Determine the cross frequency, f
C
. Generally, fc is between
f
SW
/12 and f
SW
/6.
R
C
can be calculated by
VImREF
COUTOUT
C
AgV
fCV
R
××
××××
=
π
2
where:
V
REF
= 0.6 V.
g
m
= 470 µS.
Place the compensation zero at the domain pole, f
P
. C
C
can
be determined by
C
OUTESR
C
R
CRR
C
×+
=
)(
C
CP
is optional, and it can be used to cancel the zero caused
by the ESR of the output capacitors.
C
OUTESR
CP
R
CR
C
×
=
Compensation Network Between COMP and FB
The compensation RC network can also be placed between
COMP and FB, as shown in Figure 34.
R
ESR
R
+
g
m
C
OUT
R
TOP
R
BOT
+
A
VI
V
OUT
V
COMP
V
OUT
ADP2380
GND
COMP
FB
C
CP_EA
R
C_EA
C
C_EA
09939-034
Figure 34. Small Signal Circuit with Compensation Network Between COMP
and FB
When connecting the compensation network as shown in
Figure 34, it requires the same pole and zero as in Figure 33
to maintain the same compensation performance.
Assuming that the compensation networks of Figure 33 and
Figure 34 have the same pole and zero,
)1)(//)((
)(
)(
)1)(//(
__
____
___
___
__
__
0mBOTTOPEACEACP
EACEACEACEACP0
CCCCP0
0mBOTTOPEACPEACEAC
EACPEACEAC0CPCC0
m
EACEACP
EACEACCC
rgRRCC
CRCCr
CRCCr
rgRRCCR
CCRrCCRr
g
CC
CRCR
×++
+++
=++
×+
+=
+
=
where:
r
0
is the equivalent output impedance of the transconductance
amplifier, 40 MΩ.
BOTTOP
BOTTOP
BOTTOP
RR
RR
RR
+
=//
Solve the preceding equations to obtain
))((
))((
_
_
_
_
ArCRB
CCRr
C
C
CRB
R
ArCRB
CCRr
gBC
0CC
CPCC0
EACP
EAC
CC
EAC
0CC
CPCC0
mEAC
++
=
+
=
++
×=
where:
)(1
)(
)1)(//(
0m
CCP0
0mBOTTOP
rAg
CCr
B
rgRRA
++
+
=
×+=
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