參數(shù)資料
型號(hào)： LM2746MXAX
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(yè)數(shù)： 14/24頁(yè)
文件大?。?/td> 1087K
代理商： LM2746MXAX
Application Information
(Continued)
as inductor current has fallen to the current limit threshold.
The LM2746 will continue to skip high-side MOSFET pulses
until the inductor current peak is below the current limit
threshold, at which point the system resumes normal opera-
tion.
Unlike a high-side MOSFET current sensing scheme, which
limits the peaks of inductor current, low-side current sensing
is only allowed to limit the current during the converter
off-time, when inductor current is falling. Therefore in a typi-
cal current limit plot the valleys are normally well defined, but
the peaks are variable, according to the duty cycle. The
PWM error amplifier and comparator control the off-pulse of
the high-side MOSFET, even during current limit mode,
meaning that peak inductor current can exceed the current
limit threshold. Assuming that the output inductor does not
saturate, the maximum peak inductor current during current
limit mode can be calculated with the following equation:
Where T
SW
is the inverse of switching frequency f
SW
. The
200ns term represents the minimum off-time of the duty
cycle, which ensures enough time for correct operation of
the current sensing circuitry.
In order to minimize the time period in which peak inductor
current exceeds the current limit threshold, the IC also dis-
charges the soft-start capacitor through a fixed 90 μA sink.
The output of the LM2746 internal error amplifier is limited by
the voltage on the soft-start capacitor. Hence, discharging
the soft-start capacitor reduces the maximum duty cycle D of
the controller. During severe current limit this reduction in
duty cycle will reduce the output voltage if the current limit
conditions last for an extended time. Output inductor current
will be reduced in turn to a flat level equal to the current limit
threshold. The third benefit of the soft-start capacitor dis-
charge is a smooth, controlled ramp of output voltage when
the current limit condition is cleared.
SHUTDOWN
If the shutdown pin is pulled low, (below 0.8V) the LM2746
enters shutdown mode, and discharges the soft-start capaci-
tor through a MOSFET switch. The high and low-side MOS-
FETs are turned off. The LM2746 remains in this state as
long as V
sees a logic low (see the Electrical Character-
istics table). To assure proper IC start-up the shutdown pin
should not be left floating. For normal operation this pin
should be connected directly to V
CC
or to another voltage
between 1.3V to V
CC
(see the Electrical Characteristics
table).
DESIGN CONSIDERATIONS
The following is a design procedure for all the components
needed to create the Typical Application Circuit shown on
the front page. This design converts 3.3V (V
) to 1.2V
(V
) at a maximum load of 4A with an efficiency of 89%
and a switching frequency of 300kHz. The same procedures
can be followed to create many other designs with varying
input voltages, output voltages, and load currents.
Duty Cycle Calculation
The complete duty cycle for a buck converter is defined with
the following equation:
where V
SWL
and V
SWH
are the respective forward voltage
drops that develop across the low side and high side MOS-
FETs. Assuming the inductor ripple current is 20% to 30% of
the output current, therefore:
V
SWL
= I
OUT
x R
DS(on)LOW
V
SWH
= I
OUT
x R
DS(on)HIGH
To calculate the maximum duty cycle use the estimated ’hot’
R
value of the MOSFETs, the minimum input voltage,
and maximum load. As shown in
Figure 11
, the worst case
maximum duty cycles of the LM2746 occurs at 125C junc-
tion temperature vs V
(IC control section voltage). Ensure
that the operating duty cycle is below the curve in
Figure 11
,
if this condition is not satisfied, the system will be unable to
develop the required duty cycle to derive the necessary
system power and so the output voltage will fall out of
regulation.
20147788
FIGURE 10. Current Limit Threshold
L
www.national.com
14
相關(guān)PDF資料
PDF描述
LM2753SD High Power Switched Capacitor Voltage Convertor/Flash LED Driver
LM2753 High Power Switched Capacitor Voltage Convertor/Flash LED Driver
LM2753SDX High Power Switched Capacitor Voltage Convertor/Flash LED Driver
LM2765 Switched Capacitor Voltage Converter
LM2765M6 Switched Capacitor Voltage Converter
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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(wú) 升壓:無(wú) 回掃:是 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 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(yè)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(kāi)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(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V
LM2747EVAL 功能描述:電源管理IC開(kāi)發(fā)工具 LM2747EVAL EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V
LM2747MTC 功能描述:DC/DC 開(kāi)關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)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(fēng)格: 封裝 / 箱體:CPAK
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。

采購(gòu)需求

(若只采購(gòu)一條型號(hào)，填寫一行即可)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

*型號(hào) *數(shù)量 廠商 批號(hào) 封裝
添加更多采購(gòu)

我的聯(lián)系方式

*
*
*