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參數(shù)資料
| 型號： | LP3996SD-1525 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | Dual Linear Regulator with 300mA and 150mA Outputs and Power-On-Reset |
| 中文描述： | DUAL OUTPUT, FIXED POSITIVE LDO REGULATOR, DSO10 |
| 封裝： | 3 X 3 MM, LEAD FREE, LLP-10 |
| 文件頁數(shù)： | 13/16頁 |
| 文件大?。?/td> | 871K |
| 代理商： | LP3996SD-1525 |
Application Hints
OPERATION DESCRIPTION
The LP3996 is a low quiescent current, power management
IC, designed specifically for portable applications requiring
minimum board space and smallest components. The
LP3996 contains two independently selectable LDOs. The
first is capable of sourcing 150mA at outputs between 0.8V
and 3.3V. The second can source 300mA at an output volt-
age of 0.8V to 3.3V. In addition, LDO2 contains power good
flag circuit, which monitors the output voltage and indicates
when it is within 8% of its nominal value. The flag will also act
as a power-on-reset signal and, by adding an external ca-
pacitor; a delay may be programmed for the POR output.
INPUT CAPACITOR
An input capacitor is required for stability. It is recommended
that a 1.0μF capacitor be connected between the LP3996
input pin and ground (this capacitance value may be in-
creased 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 approxi-
mately 1.0μF over the entire operating temperature range.
OUTPUT CAPACITOR
The LP3996 is designed specifically to work with very small
ceramic output capacitors. A 1.0μF ceramic capacitor (tem-
perature types Z5U, Y5V or X7R) with ESR between 5m
to
500m
, is suitable in the LP3996 application circuit.
For this device the output capacitor should be connected
between the V
OUT
pin and ground.
It is also possible to use tantalum or film capacitors at the
device output, C
OUT
(or V
OUT
), but these are not as attrac-
tive for reasons of size and cost (see the section Capacitor
Characteristics).
The output capacitor must meet the requirement for the
minimum value of capacitance and also have an ESR value
that is within the range 5m
to 500m
for stability.
NO-LOAD STABILITY
The LP3996 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 LP3996 is designed to work with ceramic capacitors on
the output to take advantage of the benefits they offer. For
capacitance values in the range of 0.47μF to 4.7μF, ceramic
capacitors are the smallest, least expensive and have the
lowest ESR values, thus making them best for eliminating
high frequency noise. The ESR of a typical 1.0μF ceramic
capacitor is in the range of 20m
to 40m
, which easily
meets the ESR requirement for stability for the LP3996.
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-
pending on the operating conditions 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. The capacitance
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 gen-
eral. As an example,
Figure 4
shows a typical graph com-
paring different capacitor case sizes in a Capacitance vs. DC
Bias plot. As shown in the graph, increasing the DC Bias
condition can result in the capacitance value falling below
the minimum value given in the recommended capacitor
specifications table (0.7μF in this case). Note that the graph
shows the capacitance out of spec for the 0402 case size
capacitor at higher bias voltages. It is therefore recom-
mended that the capacitor manufacturers’ specifications for
the nominal value capacitor are consulted for all conditions,
as some capacitor sizes (e.g. 0402) may not be suitable in
the actual application.
The ceramic capacitor’s capacitance can vary with tempera-
ture. The capacitor type X7R, which operates over a tem-
perature range of -55C to +125C, will only vary the capaci-
tance to within
±
15%. The capacitor type X5R has a similar
tolerance over a reduced temperature range of -55C to
+85C. Many large value ceramic capacitors, larger than 1μF
are manufactured with Z5U or Y5V temperature characteris-
tics. Their capacitance can drop by more than 50% as the
temperature varies from 25C to 85C. Therefore X7R is
recommended over Z5U and Y5V in applications where the
ambient temperature will change significantly above or be-
low 25C.
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
0.47μF to 4.7μF range.
20145840
FIGURE 4. Graph Showing a Typical Variation in
Capacitance vs DC Bias
L
www.national.com
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LP3996SD-1525/NOPB | 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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LP3996SD-1833/NOPB | 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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LP3996SD-2533 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LP3996SD-2533/NOPB | 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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LP3996SD-2828 | 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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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