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參數(shù)資料
| 型號： | LP2986IM-3.0 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | 2 in Diameter, 15 Amp Single Deck Rotary Switch |
| 中文描述： | FIXED/ADJUSTABLE POSITIVE LDO REGULATOR, 0.35 V DROPOUT, PDSO8 |
| 封裝： | 0.150 INCH, PLASTIC, SO-8 |
| 文件頁數(shù)： | 11/14頁 |
| 文件大?。?/td> | 412K |
| 代理商： | LP2986IM-3.0 |
Application Hints
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 (
≥
2.2 μF) is re-
quired between the LP2986 input and ground (amount of ca-
pacitance may be increased without limit).
This capacitor must be located a distance of not more than
0.5” from the input pin and returned to a clean analog
ground. Any good quality ceramic or tantalum may be used
for this capacitor.
OUTPUT CAPACITOR:
The output capacitor must meet the
requirement for minimum amount of capacitance and also
have an appropriate E.S.R. (equivalent series resistance)
value.
Curves are provided which show the allowable ESR range
as a function of load current for various output voltages and
capacitor values (see ESR curves below).
IMPORTANT:
The output capacitor must maintain its ESR in
the stable region over the full operating temperature range of
the application to assure stability.
The minimum required amount of output capacitance is
4.7 μF. Output capacitor size can be increased without limit.
It is important to remember that capacitor tolerance and
variation with temperature must be taken into consideration
when selecting an output capacitor so that the minimum re-
quired amount of output capacitance is provided over the full
operating temperature range. A good Tantalum capacitor will
show very little variation with temperature, but a ceramic
may not be as good (see next section).
CAPACITOR CHARACTERISTICS
TANTALUM:
The best choice for size, cost, and perfor-
mance are solid tantalum capacitors. Available from many
sources, their typical ESR is very close to the ideal value re-
quired on the output of many LDO regulators.
Tantalums also have good temperature stability: a 4.7 μF
was tested and showed only a 10% decline in capacitance
as the temperature was decreased from +125C to 40C.
The ESR increased only about 2:1 over the same range of
temperature.
However, it should be noted that the increasing ESR at lower
temperatures present in all tantalums can cause oscillations
when marginal quality capacitors are used (where the ESR
of the capacitor is near the upper limit of the stability range at
room temperature).
CERAMIC:
For a given amount of a capacitance, ceramics
are usually larger and more costly than tantalums.
Be warned that the ESR of a ceramic capacitor can be low
enough to cause instability: a 2.2 μF ceramic was measured
and found to have an ESR of about 15 m
.
If a ceramic capacitor is to be used on the LP2986 output, a
1
resistor should be placed in series with the capacitor to
provide a minimum ESR for the regulator.
Another disadvantage of ceramic capacitors is that their ca-
pacitance varies a lot with temperature:
Large ceramic capacitors are typically manufactured with the
Z5U temperature characteristic, which results in the capaci-
tance dropping by a 50% as the temperature goes from 25C
to 80C.
This means you have to buy a capacitor with twice the mini-
mum C
OUT
to assure stable operation up to 80C.
ALUMINUM:
The large physical size of aluminum electrolyt-
ics makes them unattractive for use with the LP2986. Their
ESR characteristics are also not well suited to the require-
ments of LDO regulators.
The ESR of an aluminum electrolytic is higher than a tanta-
lum, and it also varies greatly with temperature.
A typical aluminum electrolytic can exhibit an ESR increase
of 50X when going from 20C to 40C. Also, some alumi-
num electrolytics can not be used below 25C because the
electrolyte will freeze.
USING AN EXTERNAL RESISTIVE DIVIDER
The LP2986 output voltage can be programmed using an ex-
ternal resistive divider (see Basic Application Circuits).
The resistor connected between the Feedback pin and
ground should be 51.1k. The value for the other resistor (R1)
connected between the Feedback pin and the regulated out-
put is found using the formula:
V
OUT
= 1.23 x (1 + R1/51.1k)
It should be noted that the 25 μA of current flowing through
the external divider is approximately equal to the current
saved by not connecting the internal divider, which means
the quiescent current is not increased by using external re-
sistors.
ESR Curves For 5V Output
DS012935-6
ESR Curves For 2.5V Output
DS012935-7
www.national.com
11
相關PDF資料 |
PDF描述 |
|---|---|
| LP2986IM-3.3 | 2 in Diameter, 15 Amp Single Deck Rotary Switch |
| LP2986IM-5.0 | Micropower, 200 mA Ultra Low-Dropout Fixed or Adjustable Voltage Regulator |
| LP2986IMM-3.0 | Micropower, 200 mA Ultra Low-Dropout Fixed or Adjustable Voltage Regulator |
| LP2986IMM-3.3 | Micropower, 200 mA Ultra Low-Dropout Fixed or Adjustable Voltage Regulator |
| LP2986IMM-5.0 | Micropower, 200 mA Ultra Low-Dropout Fixed or Adjustable Voltage Regulator |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LP2986IM-5.0 | 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 |
| LP2986IM-5.0/NOPB | 功能描述:低壓差穩(wěn)壓器 - LDO 5V 200Ma Micropwr LDO Reg 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 |
| LP2986IM-5.0/NOPB | 制造商:Texas Instruments 功能描述:VOLTAGE REGULATOR IC |
| LP2986IMM-3.0 | 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 |
| LP2986IMM-3.0/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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