参数资料
型号: MP28372DS-LF
厂商: MONOLITHIC POWER SYSTEMS INC
元件分类: 稳压器
英文描述: 3 A DUAL SWITCHING CONTROLLER, 1400 kHz SWITCHING FREQ-MAX, PDSO16
封装: LEAD FREE, SOIC-16
文件页数: 12/12页
文件大小: 268K
代理商: MP28372DS-LF
MP28372 — DUAL 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
MP28372 Rev. 1.4
www.MonolithicPower.com
9
12/10/2007
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
2007 MPS. All Rights Reserved.
TM
ESR
R
2
C
2
1
f
×
π
=
In this case (as shown in Figure 2), 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:
3
R
6
C
2
1
f 3
P
×
π
=
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
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 for conditions not
listed in Table 2, 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:
FB
OUT
CS
EA
C
V
G
f
2
C
2
3
R
×
π
=
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:
C
f
3
R
2
4
3
C
×
π
>
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:
2
f
R
2
C
2
1
S
ESR
<
×
π
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:
3
R
2
C
6
C
ESR
×
=
Soft-Start
Each channel is soft-start controlled with the
SSA and SSB pins. Use capacitors to control
the ramp time using the equation:
4
C
k
9
2
.
2
RampTime
×
Ω
×
=
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.
MP28372
SWA/B
BSA/B
10nF
5V
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty
cycle operation (when
IN
OUT
V
>65%) and high
output voltage (VOUT>12V) applications.
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