參數(shù)資料
型號(hào)： MP1517
廠商： Monolithic Power Systems, Inc.
英文描述： 3A, 25V, 1.1MHz Step-Up Converter
中文描述： 第3A，25V的，為1.1MHz升壓轉(zhuǎn)換器
文件頁(yè)數(shù)： 7/13頁(yè)
文件大小： 323K
代理商： MP1517
MP1517 – 3A, 25V, 1.1MHz STEP-UP CONVERTER
MP1517 Rev. 1.4
4/28/2006
www.MonolithicPower.com
7
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
2006 MPS. All Rights Reserved.
Use an input capacitor value greater than 10μF.
The capacitor can be electrolytic, tantalum or
ceramic. However since it absorbs the input
switching current it requires an adequate ripple
current rating. Use a capacitor with RMS current
rating greater than the inductor ripple current.
To insure stable operation place the input
capacitor as close to the IC as possible.
Alternately a smaller high quality ceramic 0.1μF
capacitor may be placed closer to the IC with the
larger capacitor placed further away. If using this
technique, it is recommended that the larger
capacitor be a tantalum or electrolytic type. All
ceramic capacitors should be placed close to the
MP1517.
Selecting the Output Capacitor
The output capacitor is required to maintain the
DC output voltage. Low ESR capacitors are
preferred to keep the output voltage ripple to a
minimum. The characteristic of the output
capacitor also affects the stability of the regulation
control system. Ceramic, tantalum, or low ESR
electrolytic capacitors are recommended. In the
case of ceramic capacitors, the impedance of the
capacitor at the switching frequency is dominated
by the capacitance, and so the output voltage
ripple is mostly independent of the ESR. The
output voltage ripple is calculated as:
(
×
)
SW
UT
O
IN
UT
2
O
C
LOAD
V
RIPPLE
V
f
V
V
I
×
×
=
Where V
RIPPLE
is the output ripple voltage, V
IN
and
V
OUT
are the DC input and output voltages
respectively, I
LOAD
is the load current, f
SW
is the
switching frequency, and C2 is the capacitance of
the output capacitor.
In the case of tantalum or low-ESR electrolytic
capacitors, the ESR dominates the impedance at
the switching frequency, and so the output ripple
is calculated as:
×
+
×
×
×
=
IN
OUT
ESR
SW
OUT
IN
OUT
LOAD
RIPPLE
V
V
V
R
2
C
f
V
)
V
V
(
I
Where R
ESR
is the equivalent series resistance of
the output capacitors.
Choose an output capacitor to satisfy the output
ripple and load transient requirements of the
design. Place the output capacitor close to SW
to minimize the AC loop and switching noise.
Selecting the Diode
The output rectifier diode supplies current to the
inductor when the internal MOSFET is off. To
reduce losses due to diode forward voltage and
recovery time, use a Schottky diode. Choose a
diode whose maximum reverse voltage rating is
greater than the maximum output voltage. The
rated average forward current needs to be
equal to or greater than the load current.
Selecting the Soft-Start Capacitor
The soft-start period is determined by the equation:
C4
×
0.275
=
t
SS
Where C
SS
(in nF) is the soft-start capacitor
from SS to SGND, and t
SS
(in ms) is the
soft-start period.
Determine the capacitor required for a given
soft-start period by the equation:
SS
t
×
3.64
=
C4
It is recommended that values between 10nF and
22nF for C
SS
be used to set the soft-start period.
Compensation
The output of the transconductance error
amplifier (COMP) is used to compensate the
regulation control system. The system uses two
poles and one zero to stabilize the control loop.
The poles are f
P1
set by the output capacitor
and load resistance and f
P2
set by the
compensation capacitor C3. The zero f
Z1
is set
by the compensation capacitor C3 and the
compensation resistor R3.
These are determined by the equations:
f
P1
=
LOAD
R
C2
×
1
×
π
f
P2
=
VEA
EA
A
C3
×
2
G
×
π
×
f
Z1
=
R3
×
C3
×
2
1
π
×
Where R
LOAD
is the load resistance, G
EA
is the
error amplifier transconductance, and A
VEA
is
the error amplifier voltage gain.
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