MP1593DN データシートの表示（PDF） - Monolithic Power Systems
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MP1593DN Datasheet PDF : 11 Pages
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MP1593 – 3A, 28V, 385KHz STEP-DOWN CONVERTER
Compensation Components
The MP1593 employs current mode control for
easy compensation and fast transient response.
The system stability and transient response are
controlled through the COMP pin. COMP 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:
A VDC
= RLOAD
× GCS
× A VEA
×
VFB
VOUT
Where AVEA is the error amplifier voltage gain,
GCS is the current sense transconductance and
RLOAD is the load resistor value.
The system has two poles of importance. One
is due to the compensation capacitor (C3) and
the output resistor of error amplifier, while the
other is due to the output capacitor and the load
resistor. These poles are located at:
fP1
=
GEA
2π × C3 × A VEA
fP2
=
1
2π × C2 × RLOAD
Where GEA is the error amplifier
transconductance.
The system has one zero of importance, due to
the compensation capacitor (C3) and the
compensation resistor (R3). This zero is located
at:
fZ1
=
1
2π × C3 × R3
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:
fESR
=
1
2π × C2 × RESR
In this case (as shown in Figure 3), a third pole
set by the compensation capacitor (C6) and the
compensation resistor (R3) is used to
compensate the effect of the ESR zero on the
loop gain. This pole is located at:
fP3
=
1
2π × C6 × R3
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 unity gain) is
important.
Lower crossover frequencies result in slower
line and load transient responses, while higher
crossover frequencies could cause system
instability. A good standard is to set the
crossover frequency to approximately one-tenth
of the switching frequency. The switching
frequency for the MP1593 is 385KHz, so the
desired crossover frequency is around 38KHz.
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 been optimized for fast transient
responses and good stability at given
conditions.
MP1593 Rev. 1.9
www.MonolithicPower.com
8
9/14/2006
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© 2006 MPS. All Rights Reserved.
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