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参数资料
| 型号： | LM2641-ADJMDC |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | DUAL SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, UUC |
| 封装： | DIE |
| 文件页数： | 6/22页 |
| 文件大小： | 531K |
| 代理商： | LM2641-ADJMDC |
Application Information (Continued)
The components shown will add poles and zeros to the loop
gain as given by the following equations:
C10 adds a pole whose frequency is given by:
f
p(C10) = 1 / [2π X C10 (R11 + 160k) ]
C12 adds a pole whose frequency is given by:
f
p(C12) = 1 / [2π X C12 (R11 || 160k) ]
R11 adds a zero whose frequency is given by:
f
z(R11) = 1 / [2π X R11 (C10 + C12) ]
The output capacitor adds both a pole and a zero to the loop:
f
p(COUT) = 1/[2π XRL XCOUT]
f
z(ESR) = 1 / [2π XESRXCOUT]
Where R
L is the load resistance, and ESR is the equivalent
series resistance of the output capacitor(s).
The function of the compensation components will be ex-
plained in a qualitative discussion of a typical loop gain plot
for an LM2641 application, as illustrated in
C10 and R11 form a pole and a zero. Changing the value of
C10 moves the frequency of both the pole and the zero.
Changing R11 moves the zero without significantly affecting
the pole.
The C10 pole is typically referred to as the dominant pole,
and its primary function is to roll off loop gain and reduce the
bandwidth.
The R11 zero is required to add some positive phase shift to
offset some of the negative phase shift from the two
low-frequency poles. Without this zero, these two poles
would cause 180 of phase shift at the unity-gain crossover,
which is clearly unstable. Best results are typically obtained
if R11 is selected such that the frequency of f
z(R11) is in the
range of f
c/4 to fc where fc is the unity-gain crossover fre-
quency.
The output capacitor (along with the load resistance R
L)
forms a pole shown as f
p(COUT). Although the frequency of
this pole varies with R
L, the loop gain also varies proportion-
ally which means the unity-gain crossover frequency stays
essentially constant regardless of R
L value.
C12 can be used to create an additional pole most often
used for bypassing high-frequency switching noise on the
COMP pin. In many applications, this capacitor is unneces-
sary.
If C12 is used, best results are obtained if the frequency of
the pole is set in the range F
OSC/2 to 2FOSC. This will provide
bypassing for the high-frequency noise caused by switching
transitions, but add only a small amount of negative phase
shift at the unity-gain crossover frequency.
The ESR of C
OUT (as well as the capacitance of COUT) form
the zero f
z(ESR), which typically falls somewhere between
10kHz and 50kHz. This zero is very important, as it cancels
phase shift caused by the high-frequency pole f
p(HF). It is
important to select C
OUT with the correct value of capaci-
tance and ESR to place this zero near f
c (typical range fc/2 to
f
c).
As an example, we will present an analysis of the loop gain
plot for a 3.3V design. Values used for calculations are:
V
IN = 12V
V
OUT = 3.3V @ 4A
C
OUT = C14 + C16 = 200 F
ESR=60 m
(each) = 30m total
F
OSC = 300kHz
f
p(HF) 40kHz
R13 = 20m
L2 = 6.8 H
R
L = 0.825
DC gain = 55dB
The values of compensation components will be: C10 =
2200 pF, R11 = 8.2k, and C12 will not be used. Using this
data, the poles and zeros are calculated:
f
p(C10) = 1 / [2π X C10 (R11 + 160k) ] = 430Hz
f
z(R11) = 1 / [2π X R11 (C10 + C12) ] = 8.8kHz
f
p(COUT) = 1/[2π XRL XCOUT] = 960Hz
f
z(ESR) = 1 / [2π XESRXCOUT] = 27kHz
f
p(HF) 40kHz
Using these values, the calculated gain plot is shown in
10094905
FIGURE 4. Typical Compensation Network
10094906
FIGURE 5. Typical Loop Gain Plot
LM2641
www.national.com
14
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM2641MTC-ADJ | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| LM2641MTC-ADJ/NOPB | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| LM2641MTCX-ADJ | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| LM2641MTCX-ADJ/NOPB | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| LM2642 | 制造商:未知厂家 制造商全称:未知厂家 功能描述: |
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