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參數(shù)資料
| 型號： | LM2647MTC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual Synchronous Buck Regulator Controller |
| 中文描述： | DUAL SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | TSSOP-28 |
| 文件頁數(shù)： | 22/25頁 |
| 文件大?。?/td> | 763K |
| 代理商： | LM2647MTC |
Application Information
(Continued)
MODULATOR GAIN/COMPENSATION
The modulator gain is plotted out for various typical values of
components in Typical Performance characteristics. The
curves were based on the following information. The plant/
modulator gain ‘G’ is:
where Ro is the load resistance, s = j
ω
, and
A1 = LC*(Ro + esr)
A2 = {L + R
P
C(Ro + esr) + Ro*esr*C}
A3 = R
o
+ R
P
Here esr is the Equivalent Series Resistance of the output
capacitor, Ro is the load resistance, C is the output capaci-
tance, L is the inductance, and R
P
is the resistance of the
power stage (Rds+ DCR etc, typically about 40m
). V
RAMP
is about 1.6V for the LM2647. The unity gain bandwidth of
the error amplifier is taken as 6.5MHz.
Let us assume Type 3 compensation
Figure 15
.
The design procedure is summarized in
Table 2
.
TABLE 2. Summary of Compensation Design Procedure
fp1
(C1)
fz1
fz2
fp2
fp3
Type 3
R2, C2
R1sR3, C3
R2, C1sC2
C3, R3
Resonant frequency f =
1
2
π
RC, ’s’ stands for series combination.
TABLE 3.
C1
C2
C3
R2
R3
A is a factor to shift entire Gain up or down to acheive good crossover frequency and gain. Typically set A = 0.2 here.
TABLE 4.
fp1
(0)
fz1
fdp
fz2
fdb
fp2
fesr
fp3
fsw/2
Resonant frequency f =
1
2
π
RC, ’s’ stands for series combination.
A short explanation on
Table 2
follows. For example from the
table it can be seen that the second zero is created by the
series combination of R1 and R3 resonating with C3. So the
frequency of this zero is at 1/2
π
(R1+R3)*C3. The solution for
calculating the component values follows. For example, C3
is set as
But where should the designer position the poles and zeroes
of the error amplifier, taking into account the modulator gain,
so as to achieve good closed loop characteristics A typical
scenario is also provided in
Table 4
. For example it suggests
that both the first and second zeroes should be positioned at
the point where double pole (fdb) of the output LC filter is.
This double pole is known to occur at about.
Similarly, the esr zero occurs at fesr which is at
where C is the output capacitance
Thus all the components can be calculated easily
EVALUATION BOARD DETAILS
The Bill of Materials is now provided for the LM2647 Evalu-
ation board. The schematic is the Typical Application circuit.
See
Layout Guidelines
for more guidance on preferred lay-
out practices and also refer to Application Note AN-1229.
Note that a dual FET pack has been chosen for the Evalu-
ation Board.
The Evaluation board has two outputs V
O1
= 5V and V
O2
=
3.3V as discussed under Setting Output Voltage section. The
rated load on each output is 2A continuous, and 3A peak. A
minimum load of 0.1mA should be maintained on each out-
put in SKIP mode, to ensure regulation.
20056348
FIGURE 15. Type 3 Compensation
L
www.national.com
22
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2647MTC/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM2647MTCX | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM2647MTCX/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM2648 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Two-Phase, Synchronous Step-Down 3-Channel Switching Regulator Controller |
| LM26480 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Externally Programmable Dual High-Current Step-Down DC/DC and Dual Linear Regulators |
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