Data Sheet
ADP2325
The ADP2325 uses a transconductance amplifier for the error
amplifier to compensate the system. Figure 51 shows the
simplified peak current mode control small signal circuit.
The following design guidelines show how to select the compen-
sation components, RC, CC, and CCP, for ceramic output capacitor
applications.
V
V
OUT
OUT
4. Determine the cross frequency (fC). Generally, the fC is
between fSW/12 and fSW/6.
R
TOP
5. RC can be calculated by using the following equation:
V
C
R
COMP
C
OUT
–
gm
+
–
A
VI
2×π ×VOUT ×COUT × fC
RC =
+
R
R
BOT
R
C
0.6V × gm × AVI
CP
ESR
C
C
6. Place the compensation zero at the domain pole (fP).
CC can be determined by
(
R + RESR ×COUT
)
Figure 51. Simplified Peak Current Mode Control Small Signal Circuit
CC =
RC
The compensation components, RC and CC, contribute a zero,
and the optional CCP and RC contribute an optional pole.
7. CCP is optional. It can be used to cancel the zero caused by
the ESR of the output capacitor.
The closed-loop transfer equation is as follows:
R
ESR ×COUT
1+ RC ×CC× s
RC ×CC ×CCP
RBOT
BOT + RTOP CC+ CCP
−gm
CCP
=
TV(s) =
×
×
×GVD(s)
RC
R
s × 1+
× s
CC +CCP
The ADP2325 has an internal 10 pF capacitor at the COMPx
pin; therefore, if CCP is smaller than 10 pF, no external capacitor
is required.
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