MP2363DN Monolithic Power Systems, MP2363DN Datasheet - Page 8

• Manufacturer Part Number: MP2363DN
• Description: 3A, 27V, 365khz Step-down Converter
• Manufacturer: Monolithic Power Systems

Compensation Components
MP2363 employs current mode control for easy
compensation and fast transient response. The
system stability and transient response are
controlled through the COMP pin. COMP pin is
the output of the internal transconductance
error amplifier. A series capacitor-resistor
combination sets a pole-zero combination to
control the characteristics of the control system.
The DC gain of the voltage feedback loop is
given by:
Where A
400V/V;
transconductance, 7A/V, and R
resistor value.
The system has two poles of importance. One
is due to the compensation capacitor (C3) and
the output resistor of error amplifier, and the
other is due to the output capacitor and the load
resistor. These poles are located at:
Where
transconductance, 800µA/V.
The system has one zero of importance, due to
the compensation capacitor (C3) and the
compensation resistor (R3). This zero is located
at:
The system may have another zero of
importance, if the output capacitor has a large
capacitance and/or a high ESR value. The zero,
due to the ESR and capacitance of the output
capacitor, is located at:
MP2363 Rev. 1.0
6/15/2006
A
VEA
VDC
G
G
EA
is the error amplifier voltage gain,
=
CS
f
f
ESR
f
P
R
P
2
f
1
LOAD
Z
=
1
=
is
=
=
is
2
2
2
π
π
2
×
π
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
×
π
×
G
×
C
×
C
the
CS
the
G
C
C
2
3
1
EA
1
2
3
×
×
1
×
×
R
×
A
A
R
R
LOAD
VEA
VEA
ESR
error
3
current
LOAD
×
V
V
OUT
is the load
FB
© 2006 MPS. All Rights Reserved.
amplifier
www.MonolithicPower.com
sense
MP2363 – 3A, 27V, 365KHz STEP-DOWN CONVERTER
In this case, a third pole set by the
compensation
compensation
compensate the effect of the ESR zero on the
loop gain. This pole is located at:
The goal of compensation design is to shape
the converter transfer function to get a desired
loop gain. The system crossover frequency
where the feedback loop has the unity gain is
important.
Lower crossover frequencies result in slower
line and load transient responses, while higher
crossover
instability. A good rule of thumb is to set the
crossover frequency to approximately one-tenth
of the switching frequency. Switching frequency
for the MP2363 is 365KHz, so the desired
crossover frequency is around 36.5KHz.
Table 3 lists the typical values of compensation
components for some standard output voltages
with various output capacitors and inductors.
The values of the compensation components
have
responses
conditions.
Table 3—Compensation Values for Typical
V
1.8V
2.5V
3.3V
12V
Output Voltage/Capacitor Combinations
5V
OUT
been
4.7
6.8
10
15
4.7µH
–
–
–
–
L
15µH
20µH
10µH
10µH
frequencies
and
optimized
f
P
resistor
3
capacitor
Ceramic
Ceramic
Ceramic
Ceramic
Ceramic
=
22µFx2
22µFx2
22µFx2
100µF
good
47µF
C2
2
π
×
C
1
can
6
(R3)
3.32kΩ 6.8nF
4.02kΩ 8.2nF
6.49kΩ
for
stability
5.6kΩ
×
15kΩ
R3
R
(C6)
3
cause
fast
is
3.3nF
4.7nF
10nF
C3
and
at
used
transient
system
None
None
None
None
None
given
C6
the
to
8