參數(shù)資料
型號(hào)： LM2574HVN-ADJ
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類(lèi)： 穩(wěn)壓器
英文描述： SIMPLE SWITCHER⑩ 0.5A Step-Down Voltage Regulator
中文描述： 1.8 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, PDIP8
封裝： DIP-8
文件頁(yè)數(shù)： 16/24頁(yè)
文件大?。?/td> 397K
代理商： LM2574HVN-ADJ
LM2574
16
MOTOROLA ANALOG IC DEVICE DATA
Continuous and Discontinuous Mode of Operation.
The LM2574 step–down converter can operate in both the
continuous and the discontinuous modes of operation. The
regulator works in the continuous mode when loads are
relatively heavy, the current flows through the inductor
continuously and never falls to zero. Under light load
conditions, the circuit will be forced to the discontinuous
mode when inductor current falls to zero for certain period of
time (see Figure 24 and Figure 25). Each mode has
distinctively different operating characteristics, which can
affect the regulator performance and requirements. In many
cases the preferred mode of operation is the continuous
mode. It offers greater output power, lower peak currents in
the switch, inductor and diode, and can have a lower output
ripple voltage. On the other hand it does require larger
inductor values to keep the inductor current flowing
continuously, especially at low output load currents and/or
high input voltages.
To simplify the inductor selection process, an inductor
selection guide for the LM2574 regulator was added to this
data sheet (Figures 19 through 23). This guide assumes that
the regulator is operating in the continuous mode, and
selects an inductor that will allow a peak–to–peak inductor
ripple current to be a certain percentage of the maximum
design load current. This percentage is allowed to change as
different design load currents are selected. For light loads
(less than approximately 0.2 A) it may be desirable to operate
the regulator in the discontinuous mode, because the
inductor value and size can be kept relatively low.
Consequently, the percentage of inductor peak–to–peak
current increases. This discontinuous mode of operation is
perfectly acceptable for this type of switching converter. Any
buck regulator will be forced to enter discontinuous mode if
the load current is light enough.
Selecting the Right Inductor Style
Some important considerations when selecting a core
type are core material, cost, the output power of the power
supply, the physical volume the inductor must fit within, and
the amount of EMI (Electro–Magnetic Interference) shielding
that the core must provide. There are many different styles of
inductors available, such as pot core, E–core, toroid and
bobbin core, as well as different core materials such as
ferrites and powdered iron from different manufacturers.
For high quality design regulators the toroid core seems to
be the best choice. Since the magnetic flux is contained
within the core, it generates less EMI, reducing noise
problems in sensitive circuits. The least expensive is the
bobbin core type, which consists of wire wound on a ferrite
rod core. This type of inductor generates more EMI due to the
fact that its core is open, and the magnetic flux is not
contained within the core.
When multiple switching regulators are located on the
same printed circuit board, open core magnetics can cause
interference between two or more of the regulator circuits,
especially at high currents due to mutual coupling. A toroid,
pot core or E–core (closed magnetic structure) should be
used in such applications.
Do Not Operate an Inductor Beyond its Maximum
Rated Current
Exceeding an inductor’s maximum current rating may
cause the inductor to overheat because of the copper wire
losses, or the core may saturate. Core saturation occurs
when the flux density is too high and consequently the cross
sectional area of the core can no longer support additional
lines of magnetic flux.
This causes the permeability of the core to drop, the
inductance value decreases rapidly and the inductor begins
to look mainly resistive. It has only the dc resistance of the
winding. This can cause the switch current to rise very rapidly
and force the LM2574 internal switch into cycle–by–cycle
current limit, thus reducing the dc output load current. This
can also result in overheating of the inductor and/or the
LM2574. Different inductor types have different saturation
characteristics, and this should be kept in mind when
selecting an inductor.
HORIZONTAL TIME BASE: 5.0
μ
s/DIV
V
Figure 24. Continuous Mode Switching
Current Waveforms
0.5 A
0 A
0.5 A
0 A
Power
Switch
Current
Waveform
Inductor
Current
Waveform
V
HORIZONTAL TIME BASE: 5.0
μ
s/DIV
Figure 25. Continuous Mode Switching
Current Waveforms
0.1 A
0 A
0.1 A
0 A
Power
Switch
Current
Waveform
Inductor
Current
Waveform
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM2574HVN-ADJ 制造商:Texas Instruments 功能描述:IC SWITCHING REG ADJ 2574 DIP8
LM2574HVN-ADJ/NOPB 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 0.5A STEP-DOWN VLTG REG RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
LM2574HVN-ADJ-ND 制造商:National Semiconductor Corporation 功能描述:
LM2574M-12 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
LM2574M-12/NOPB 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
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