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參數(shù)資料
| 型號： | LP3994LDX-1.5 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | 50mA CMOS Voltage Regulator with Enable Control |
| 中文描述： | 1.5 V FIXED POSITIVE REGULATOR, DSO6 |
| 文件頁數(shù)： | 9/12頁 |
| 文件大?。?/td> | 249K |
| 代理商： | LP3994LDX-1.5 |
Application Hints
EXTERNAL CAPACITORS
In common with most regulators, the LP3994 requires exter-
nal capacitors for regulator stability. The LP3994 is specifi-
cally designed for portable applications requiring minimum
board space and smallest components. These capacitors
must be correctly selected for good performance and to
ensure that their value remains within specification over the
full operating range.
INPUT CAPACITOR
An input capacitor is required for optimum operation and to
ensure stability within the range of specified transient condi-
tions. It is recommended that a 1.0μF capacitor be con-
nected between the LP3994 input pin and ground (this ca-
pacitance value may be increased without limit).
This capacitor must be located a distance of not more than
1cm from the input pin and returned to a clean analogue
ground.Any good quality ceramic, tantalum, or film capacitor
may be used at the input.
Important:
Tantalum capacitors can suffer catastrophic fail-
ures due to surge current when connected to a low-
impedance source of power (like a battery or a very large
capacitor). If a tantalum capacitor is used at the input, it must
be guaranteed by the manufacturer to have a surge current
rating sufficient for the application.
There are no requirements for the ESR (Equivalent Series
Resistance) on the input capacitor, but tolerance and tem-
perature coefficient must be considered when selecting the
capacitor to ensure the capacitance will remain
)
1.0μF over
the entire operating temperature range.
OUTPUT CAPACITOR
Correct selection of the output capacitor is essential to en-
sure stable operation in the intended application.
The output capacitor must meet all the requirements speci-
fied in the recommended capacitor table over all conditions
in the application. These conditions include DC-Bias, fre-
quency and temperature. Unstable operation may result if
the capacitance drops below the minimum specified value.
(See the Capacitor Characteristics section).
The LP3994 is designed specifically to work with very small
ceramic output capacitors. A 1.0μF ceramic capacitor (type
X7R) with ESR between 5m
to 500m
, is suitable in the
LP3994 application circuit. X5R type capacitors may be used
but have a narrower temperature range. With these capaci-
tors and others types (Y5V, Z6U) that may be used, selection
of the capacitor for any application is dependant on the
range of operating conditions and temperature range for that
application. (see section on Capacitor Characteristics).
It may also be possible to use tantalum or film capacitors at
the device output, C
(or V
), but these are not as
attractive for reasons of size and cost (see the section
Capacitor Characteristics).
It is also recommended that the output capacitor be placed
within 1cm from the output pin and returned to a clean
ground line.
NO-LOAD STABILITY
The LP3994 will remain stable and in regulation with no
external load. This is an important consideration in some
circuits, for example CMOS RAM keep-alive applications.
CAPACITOR CHARACTERISTICS
The LP3994 is designed to work with ceramic capacitors on
the input and output to take advantage of the benefits they
offer. For capacitance values around the 1μF value, ceramic
capacitors give the circuit designer the best design options in
terms of low cost and minimal area. Ceramic capacitors
have the lowest ESR values, thus making them best for
eliminating high frequency noise. The ESR of a typical 1μF
ceramic capacitor is in the range of 20m
to 40m
, which
easily meets the ESR requirement for stability for the
LP3994.
For both input and output capacitors careful interpretation of
the capacitor specification is required to ensure correct de-
vice operation. The capacitor value can change greatly de-
pendant on the conditions of operation and capacitor type.
In particular the output capacitor selection should take ac-
count of all the capacitor parameters to ensure that the
specification is met within the application. Capacitance value
can vary with DC bias conditions as well as temperature and
frequency of operation. Capacitor values will also show
some decrease over time due to aging. The capacitor pa-
rameters are also dependant on the particular case size with
smaller sizes giving poorer performance figures in general.A
study of manufacturers data on 0402 case size capacitors
shows that these devices may drop below the minimum
specified capacitance due to DC-Bias conditions in conjunc-
tion with other parameters such as temperature and are thus
not recommended for use.
The temperature performance of ceramic capacitors varies
by type. Capacitor type X7R is specified with a tolerance of
±
15% over the temperature range -55
o
C to +125
o
C. The
X5R has a similar tolerance over the reduced temperature
range of -55
o
C to +85
o
C. Most large value ceramic capaci-
tors (
≥
2.2μF) are manufactured with Z5U or Y5V tempera-
ture characteristics, which results in the capacitance drop-
ping by more than 50% as the temperature goes from 25C
to 85C. Therefore X7R is recommended over these other
capacitor types in applications where the temperature will
change significantly above or below 25
o
C.
Tantalum capacitors are less desirable than ceramic for use
as output capacitors because they are more expensive when
comparing equivalent capacitance and voltage ratings in the
1μF to 4.7μF range.
Another important consideration is that tantalum capacitors
have higher ESR values than equivalent size ceramics. This
means that while it may be possible to find a tantalum
capacitor with an ESR value within the stable range, it would
have to be larger in capacitance (which means bigger and
more costly) than a ceramic capacitor with the same ESR
value. It should also be noted that the ESR of a typical
tantalum will increase about 2:1 as the temperature goes
from 25C down to -40C, so some guard band must be
allowed.
L
www.national.com
9
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LP3994TL-1.5 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| LP3994TLX-1.5 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| LP3994TLX-1.8 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| LP3995AULN-1.8 WAF | 制造商:Texas Instruments 功能描述: |
| LP3995ILD-1.5 | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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