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參數(shù)資料
| 型號： | SP6120 |
| 英文描述： | Fixed Frequency, Voltage Mode, Synchronous PWM Controller(固定頻率，電壓模式同步PWM（脈寬調(diào)制控制器）) |
| 中文描述： | 固定頻率，電壓模式，同步PWM控制器（固定頻率，電壓模式同步的PWM（脈寬調(diào)制控制器）） |
| 文件頁數(shù)： | 15/20頁 |
| 文件大?。?/td> | 187K |
| 代理商： | SP6120 |
15
P
Rev. 2/15/01
SP6120 Low Voltage, AnyFET
TM
, Synchronous, Buck Controller Copyright 2001 Sipex Corporation
two 0.04 square inches copper pad directly
under the package, without occupying addi-
tional board space, can increase the maximum
power from approximately 1 to 1.2W. For DPAK
package, enlarging the tap mounting pad to 1 square
inches reduces the R
Θ
JA from 96
°
C/W to 40
°
C/W.
Schottky Diode Selection
When paralleled with the bottom MOSFET, an
optional Schottky diode can improve efficiency
and reduce noises. Without this Schottky diode,
the body diode of the bottom MOSFET con-
ducts the current during the non-overlap time
when both MOSFETs are turned off. Unfortu-
nately, the body diode has high forward voltage
and reverse recovery problem. The reverse re-
covery of the body diode causes additional
switching noises when the diode turns off. The
Schottky diode alleviates these noises and addi-
tionally improves efficiency thanks to its low
forward voltage. The reverse voltage across the
diode is equal to input voltage, and the diode
must be able to handle the peak current equal to
the maximum load current.
The power dissipation of the Schottky diode is
determined by
V
P
2
=
where
T
NOL
= non-overlap time between GH and GL.
V
F
= forward voltage of the Schottky diode.
s
NOL
OUT
F
diode
F
T
I
SP6120
C2
C1
R1
COMP
Figure 7. The RC network connected to the COMP pin
provides a pole and a zero to control loop.
Loop Compensation Design
The goal of loop compensation is to manipulate
loop frequency response such that its gain crosses
over 0db at a slope of –20db/dec. The SP6120
has a transconductance error amplifier and re-
quires the compensation network to be con-
nected between the COMP pin and ground, as
shown in Figure 7.
The first step of compensation design is to pick
the loop crossover frequency. High crossover
frequency is desirable for fast transient response,
but often jeopardize the system stability. Since
the SP6120 is equipped with 3% window com-
parator that takes over the control loop on tran-
sient, the crossover frequency can be selected
primarily to the satisfaction of system stability.
Crossover frequency should be higher than the
ESR zero but less than 1/5 of the switching
frequency. The ESR zero is contributed by the
ESR associated with the output capacitors and
can be determined by:
ESR
OUT
ESR
Z
R
C
f
π
2
1
)
(
=
Crossover frequency of 20kHz is a sound first
try if low ESR tantalum capacitors or poscaps
are used at the output. The next step is to calcu-
late the complex conjugate poles contributed by
the LC output filter,
OUT
LC
P
LC
f
π
2
1
)
(
=
The open loop gain of the whole system can be
divided into the gain of the error amplifier,
PWM modulator, buck converter, and feedback
resistor divider. In order to crossover at the
selected frequency fco, the gain of the error
amplifier has to compensate for the attenuation
caused by the rest of the loop at this frequency.
In the RC network shown in Figure 7, the prod-
uct of R1 and the error amplifier transconductance
determines this gain. Therefore, R1 can be de-
termined from the following equation that takes
into account the typical error amplifier
transconductance, reference voltage and PWM
ramp built into the SP6120.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SP6120_05 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Low Voltage, AnyFETTM, Synchronous,Buck Controller Ideal for 2A to 10A, High Performance, DC-DC Power Converters |
| SP612-05 | 制造商:Delphi Corporation 功能描述:WIRE STOP |
| SP612-07 | 制造商:Delphi Corporation 功能描述:LOCATOR |
| SP612-08 | 制造商:Delphi Corporation 功能描述:PIVOT PIN |
| SP6120B | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Low Voltage, AnyFETTM, Synchronous ,Buck Controller Ideal for 2A to 10A, High Performance, DC-DC Power Converters |
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