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參數(shù)資料
| 型號： | LM2746MXA |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Low Voltage N-Channel MOSFET Synchronous Buck Regulator Controller |
| 中文描述： | SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO14 |
| 封裝： | PLASTIC, TSSOP-14 |
| 文件頁數(shù)： | 18/24頁 |
| 文件大小： | 1087K |
| 代理商： | LM2746MXA |
Application Information
(Continued)
as high as possible. Two zeroes f
Z1
and f
Z2
are placed at the
double pole frequency to cancel the double pole phase lag.
Then, a pole, f
P1
is placed at the frequency of the ESR zero.
A final pole f
P2
is placed at one-half of the switching fre-
quency. The gain of the error amplifier transfer function is
selected to give the best bandwidth possible without violat-
ing the Nyquist stability criteria. In practice, a good crossover
point is one-fifth of the switching frequency, or 60kHz for this
example. The generic equation for the error amplifier transfer
function is:
In this equation the variableA
is a ratio of the values of the
capacitance and resistance of the compensation compo-
nents, arranged as shown in
Figure 12
. A
EA
is selected to
provide the desired bandwidth. A starting value of 80,000 for
A
EA
should give a conservative bandwidth. Increasing the
value will increase the bandwidth, but will also decrease
phase margin. Designs with 45-60 are usually best because
they represent a good tradeoff between bandwidth and
phase margin. In general, phase margin is lowest and gain
highest (worst-case) for maximum input voltage and mini-
mum output current. One method to select A
is to use an
iterative process beginning with these worst-case conditions.
1.
Increase A
EA
2.
Check overall bandwidth and phase margin
3.
Change V
to minimum and recheck overall bandwidth
and phase margin
4.
Change I
to maximum and recheck overall bandwidth
and phase margin
The process ends when both bandwidth and phase margin
are sufficiently high. For this example input voltage can vary
from 3.0 to 3.6V and output current can vary from 0 to 4A,
and after a few iterations a moderate gain factor of 101dB is
used.
The error amplifier of the LM2746 has a unity-gain band-
width of 9MHz. In order to model the effect of this limitation,
the open-loop gain can be calculated as:
The new error amplifier transfer function that takes into
account unity-gain bandwidth is:
The gain and phase of the error amplifier are shown in
Figure 14
.
In VM regulators, the top feedback resistor R
FB2
forms a part
of the compensation. Setting R
to 10k
±
1% usually
gives values for the other compensation resistors and ca-
pacitors that fall within a reasonable range. (Capacitances
>
1pF, resistances
<
1M
) C
, C
, C
, R
, and R
are
selected to provide the poles and zeroes at the desired
frequencies, using the following equations:
20147774
20147775
FIGURE 14. Error Amp. Gain and Phase
L
www.national.com
18
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2746MXA/NOPB | 功能描述:IC REG CTRLR BUCK PWM VM 14TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR) |
| LM2746MXAX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Low Voltage N-Channel MOSFET Synchronous Buck Regulator Controller |
| LM2746MXAX/NOPB | 功能描述:IC REG CTRLR BUCK PWM VM 14TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:100% 電源電壓:8.2 V ~ 30 V 降壓:無 升壓:無 回掃:是 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:是 工作溫度:0°C ~ 70°C 封裝/外殼:8-DIP（0.300"，7.62mm） 包裝:管件 產(chǎn)品目錄頁面:1316 (CN2011-ZH PDF) |
| LM2747 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Synchronous Buck Controller with Pre-bias Startup, and Optional Clock Synchronization |
| LM2747-19AEVAL | 功能描述:電源管理IC開發(fā)工具 LM2747 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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