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參數(shù)資料
| 型號： | LP3918TLX-L |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 電源管理 |
| 英文描述： | Battery Charge Management and Regulator Unit |
| 中文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PBGA25 |
| 封裝： | 2.50 X 2.50 MM, MICRO, SMD-25 |
| 文件頁數(shù)： | 17/30頁 |
| 文件大?。?/td> | 1292K |
| 代理商： | LP3918TLX-L |
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INPUT CAPACITOR
Input capacitors are required for correct operation. It is rec-
ommended that a 10F capacitor be connected between
each of the voltage input pins and ground (this capacitance
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. A ceramic capacitor
is recommended although a good quality tantalum or film ca-
pacitor 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 surge current rat-
ing sufficent for the application. There are no requirements for
the ESR (Equivalent Series Resistance) on the input capaci-
tor, but tolerance and temparature coefficient must be con-
sidered when selecting the capacitor to ensure the capaci-
tance will remain within its operational range over the entire
operating temperature range and conditions.
Output Capacitor
Correct selection of the output capacitor is critical to ensure
stable operation in the intended application.The output ca-
pacitor must meet all the requirements specified in the rec-
ommended capacitor table over all conditions in the applica-
tion. These conditions include DC-bias, frequency and
temperature. Unstable operation will result if the capacitance
drops below the minimum specified value. The LP3918 is de-
signed specifically to work with very small ceramic output
capacitors. The LDO's on the LP3918 are specifically de-
signed to be used with X7R and X5R type capacitors. With
these capacitors selection of the capacitor for the application
is dependant on the range of operating conditions and tem-
perature range for that application. (See section on Capacitor
Characteristics). It is also recommended that the output ca-
pacitor be placed within 1cm from the output pin and returned
to a clean ground line.
Capacitor Characteristics
The LDO's on the LP3918 are designed to work with ceramic
capacitors on the input and output to take advantage of the
benifits they offer. For capacitance values around 1F, ce-
ramic capacitors give the circuit designer the best design
options in terms of low cost and minimal area. For both input
and output capacitors careful interpretation of the capacitor
specification is required to ensure correct device operation.
The capacitor value can change greatly dependant on the
conditions of operation and capacitor type. In particular to en-
sure stability, 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 parameters
are also dependant on the particular case size with smaller
sizes giving poorer performance figures in general.
20211612
FIGURE 5. Graph Showing A Typical Variation in
Capacitance vs DC Bias
As an example Figure 5 shows a typical graph showing a
comparison of capacitor case sizes in a Capacitance vs DC
Bias plot. As shown in the graph, as a result of DC Bias con-
dition the capacitance value may drop below minimum ca-
pacitance value given in the recommended capacitor table
(0.7F in this case). Note that the graph shows the capaci-
tance out of spec for 0402 case size capacitor at higher bias
voltages. It is therefore recommended that the capacitor man-
ufacturers 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. Ceramic
capacitors have the lowest ESR values, thus making them
best for eliminating high frequency noise. The ESR of a typical
1F ceramic capacitor is in the range of 20m
to 40m, and
also meets the ESR requirements for stability. The tempera-
ture performance of ceramic capacitors varies by type. Ca-
pacitor type X7R is specified with a tolerance of ±15% over
temperature range -55C to +125C. The X5R has similar tol-
erance over the reduced temperature range -55C to +85C.
Most large value ceramic capacitors (<2.2F) are manufac-
tured with Z5U or Y5V temperature characteristics, which
results in the capacitance dropping by more than 50% as the
temperature goes from 25C to 85C. Therefore X7R is rec-
ommended over these other capacitor types in applications
where the temperature will change significally above or below
25C.
www.national.com
24
LP3918
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| LP3919 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:CDMA Power Management Unit |
| LP3919RL-A/NOPB | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| LP3919RL-B/NOPB | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| LP3919RL-C/NOPB | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| LP3919RL-D/NOPB | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
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