MP2358 Ver la hoja de datos (PDF) - Monolithic Power Systems
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MP2358 Datasheet PDF : 9 Pages
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TM
MP2358 – 2A, 23V, 370KHz STEP-DOWN CONVERTER
In this case, 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 the unity gain is
important.
Lower crossover frequencies result in slower
line and load transient responses, while higher
crossover frequencies could cause the system
to become unstable. A good rule of thumb is to
set the crossover frequency to below one-tenth
of the switching frequency. To optimize the
compensation components, the following
procedure can be used:
1. Choose the compensation resistor (R3) to set
the desired crossover frequency. Determine the
R3 value by the following equation:
R3 = 2π × C2 × fC × VOUT
GEA × GCS VFB
Where fC is the desired crossover frequency,
which is typically less than one tenth of the
switching frequency.
2. Choose the compensation capacitor (C3) to
achieve the desired phase margin. For
applications with typical inductor values, setting
the compensation zero, fZ1, to below one forth
of the crossover frequency provides sufficient
phase margin. Determine the C3 value by the
following equation:
C3 >
2
π × R3 × fC
Where R3 is the compensation resistor value.
3. Determine if the second compensation
capacitor (C6) is required. It is required if the
ESR zero of the output capacitor is located at
less than half of the switching frequency, or the
following relationship is valid:
1
< fS
2π × C2 × RESR 2
If this is the case, then add the second
compensation capacitor (C6) to set the pole fP3
at the location of the ESR zero. Determine the
C6 value by the equation:
C6 = C2 × RESR
R3
External Bootstrap Diode
It is recommended that an external boost diode
be added when the system has a 5V fixed input
or the power supply generates a 5V output.
This helps improve the efficiency of the
MP2358 regulator. The bootstrap diode can be
a low cost one such as IN4148 or BAT54.
5V
BS
MP2358
SW
10nF
MP2358_F02
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty
cycle operation (when VOUT >65%) and high
VIN
output voltage (VOUT>12V) applications.
MP2358 Rev. 1.3
www.MonolithicPower.com
8
3/23/2006
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