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參數(shù)資料
| 型號： | LP3873ET-1.8 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | 3A Fast Ultra Low Dropout Linear Regulators |
| 中文描述： | 1.8 V FIXED POSITIVE LDO REGULATOR, 1.2 V DROPOUT, PSFM5 |
| 封裝： | TO-220, 5 PIN |
| 文件頁數(shù)： | 11/16頁 |
| 文件大小： | 365K |
| 代理商： | LP3873ET-1.8 |
Application Hints
V
IN
RESTRICTIONS FOR PROPER START-UP
To prevent misoperation, ensure that V
is below 50mV
before start-up is initiated. This scenario can occur in sys-
tems with a backup battery using reverse-biased "blocking"
diodes which may allow enough leakage current to flow into
the V
IN
node to raise it’s voltage slightly above ground when
the main power is removed. Using low leakage diodes or a
resistive pull down can prevent the voltage at V
IN
from rising
above 50mV. Large bulk capacitors connected to V
IN
may
also cause a start-up problem if they do not discharge fully
before re-start is initiated (but only if V
IN
is allowed to fall
below 1V). A resistor connected across the capacitor will
allow it to discharge more quickly. It should be noted that the
probability of a "false start" caused by incorrect logic states
is extremely low.
EXTERNAL CAPACITORS
Like any low-dropout regulator, external capacitors are re-
quired to assure stability. these capacitors must be correctly
selected for proper performance.
INPUT CAPACITOR:
An input capacitor of at least 1μF is
required. Ceramic or Tantalum may be used, and capaci-
tance may be increased without limit
OUTPUT CAPACITOR:
An output capacitor is required for
loop stability. It must be located less than 1 cm from the
device and connected directly to the output and ground pins
using traces which have no other currents flowing through
them (see PCB Layout section).
The minimum value of the output capacitance that can be
used for stable full-load operation is 10 μF, but it may be
increased without limit. The output capacitor must have an
ESR value as shown in the stable region of the curve (be-
low).
ESR Curve
20060570
SELECTING A CAPACITOR
It is important to note that capacitance tolerance and varia-
tion with temperature must be taken into consideration when
selecting a capacitor so that the minimum required amount
of capacitance is provided over the full operating tempera-
ture range. In general, a good Tantalum capacitor will show
very little capacitance variation with temperature, but a ce-
ramic may not be as good (depending on dielectric type).
Aluminum electrolytics also typically have large temperature
variation of capacitance value.
Equally important to consider is a capacitor’s ESR change
with temperature: this is not an issue with ceramics, as their
ESR is extremely low. However, it is very important in Tan-
talum and aluminum electrolytic capacitors. Both show in-
creasing ESR at colder temperatures, but the increase in
aluminum electrolytic capacitors is so severe they may not
be feasible for some applications (see Capacitor Character-
istics Section).
CAPACITOR CHARACTERISTICS
CERAMIC:
For values of capacitance in the 10 to 100 μF
range, ceramics are usually larger and more costly than
tantalums but give superior AC performance for bypassing
high frequency noise because of very low ESR (typically less
than 10 m
). However, some dielectric types do not have
good capacitance characteristics as a function of voltage
and temperature.
Z5U and Y5V dielectric ceramics have capacitance that
drops severely with applied voltage. A typical Z5U or Y5V
capacitor can lose 60% of its rated capacitance with half of
the rated voltage applied to it. The Z5U and Y5V also exhibit
a severe temperature effect, losing more than 50% of nomi-
nal capacitance at high and low limits of the temperature
range.
X7R and X5R dielectric ceramic capacitors are strongly rec-
ommended if ceramics are used, as they typically maintain a
capacitance range within
±
20% of nominal over full operat-
ing ratings of temperature and voltage. Of course, they are
typically larger and more costly than Z5U/Y5U types for a
given voltage and capacitance.
TANTALUM:
Solid Tantalum capacitors are recommended
for use on the output because their typical ESR is very close
to the ideal value required for loop compensation. They also
work well as input capacitors if selected to meet the ESR
requirements previously listed.
Tantalums also have good temperature stability: a good
quality Tantalum will typically show a capacitance value that
varies less than 10-15% across the full temperature range of
125C to 40C. ESR will vary only about 2X going from the
high to low temperature limits.
The increasing ESR at lower temperatures can cause oscil-
lations when marginal quality capacitors are used (if the ESR
of the capacitor is near the upper limit of the stability range at
room temperature).
ALUMINUM:
This capacitor type offers the most capaci-
tance for the money. The disadvantages are that they are
larger in physical size, not widely available in surface mount,
and have poor AC performance (especially at higher fre-
quencies) due to higher ESR and ESL.
Compared by size, the ESR of an aluminum electrolytic is
higher than either Tantalum or ceramic, and it also varies
greatly with temperature. A typical aluminum electrolytic can
exhibit an ESR increase of as much as 50X when going from
25C down to 40C.
It should also be noted that many aluminum electrolytics only
specify impedance at a frequency of 120 Hz, which indicates
they have poor high frequency performance. Only aluminum
electrolytics that have an impedance specified at a higher
frequency (between 20 kHz and 100 kHz) should be used for
the LP387X. Derating must be applied to the manufacturer’s
ESR specification, since it is typically only valid at room
temperature.
L
www.national.com
11
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LP3873ET-2.5 | 制造商:Texas Instruments 功能描述:V REG LDO 3A 2.5V 3873 TO-220-5 |
| LP3873ET-2.5/NOPB | 功能描述:IC REG LDO 2.5V 3A TO220-5 RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 系列:- 標準包裝:1 系列:- 穩(wěn)壓器拓撲結(jié)構(gòu):正，固定式 輸出電壓:4V 輸入電壓:最高 16V 電壓 - 壓降（標準）:0.28V @ 150mA 穩(wěn)壓器數(shù)量:1 電流 - 輸出:150mA 電流 - 限制（最?。?- 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:5-VFBGA 供應商設備封裝:5-uSMD 包裝:Digi-Reel® 其它名稱:LP2985AIBP-4.0DKR |
| LP3873ET-3.3 | 制造商:Texas Instruments 功能描述:V REG LDO 3A 3.3V 3873 TO-220-5 |
| LP3873ET-3.3/NOPB | 功能描述:IC REG LDO 3.3V 3A TO220-5 RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 系列:- 產(chǎn)品變化通告:Heatsink Pkg Change 09/Oct/2007 標準包裝:50 系列:- 穩(wěn)壓器拓撲結(jié)構(gòu):正，固定式 輸出電壓:24V 輸入電壓:最高 40 V 電壓 - 壓降（標準）:2V @ 1A 穩(wěn)壓器數(shù)量:1 電流 - 輸出:1A 電流 - 限制（最?。?- 工作溫度:0°C ~ 125°C 安裝類型:通孔 封裝/外殼:TO-220-3 供應商設備封裝:TO-220-3 包裝:管件 |
| LP3873ET-5.0 | 制造商:Texas Instruments 功能描述:V REG LDO 3A 5.0V 3873 TO-220-5 |
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