MP2307DN Monolithic Power Systems, MP2307DN Datasheet - Page 9

• Manufacturer Part Number: MP2307DN
• Description: 3A, 23V, 340khz Synchronous Rectified Step-down Converter
• Manufacturer: Monolithic Power Systems

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:
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 frequencies could cause
system instability. A good standard is to set the
crossover frequency 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 R3 by the following equation:
Where f
which is typically below one tenth of the
switching frequency.
MP2307 Rev. 1.7
3/14/2006
R
3
=
2
G
π
EA
×
C
C
×
2
is the desired crossover frequency
G
×
CS
TM
f
f
C
ESR
MP2307 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER
f
×
f
P
Z
resistor
3
1
capacitor
V
V
=
OUT
=
=
FB
2
2
2
π
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
π
π
<
×
×
×
2
C
C
C
π
1
1
2
3
6
1
(R3)
×
G
×
×
×
C
EA
R
R
R
2
(C6)
ESR
3
3
×
×
G
0
1 .
is
CS
×
f
and
S
used
© 2006 MPS. All Rights Reserved.
×
V
V
www.MonolithicPower.com
OUT
FB
the
to
2. Choose the compensation capacitor (C3) to
achieve
applications with typical inductor values, setting
the compensation zero (f
the crossover frequency provides sufficient
phase margin.
Determine C3 by the following equation:
Where R3 is the compensation resistor.
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:
If this is the case, then add the second
compensation capacitor (C6) to set the pole f
at the location of the ESR zero. Determine C6
by the equation:
External Bootstrap Diode
It is recommended that an external bootstrap
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
regulator. The bootstrap diode can be a low
cost one such as IN4148 or BAT54.
This diode is also recommended for high duty
cycle operation (when
output voltage (V
Figure 2—External Bootstrap Diode
the
MP2307
2
desired
C
π
C
OUT
3
×
6
C
>
=
>12V) applications.
2
2
1
SW
BS
C
×
π
2
R
×
×
ESR
R
R
V
phase
Z1
4
R
V
3
3
OUT
) below one-forth of
IN
ESR
×
MP2307_F02
<
5V
f
10nF
C
>65%) and high
f
2
S
margin.
For
P3
9