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參數(shù)資料
| 型號(hào)： | LP2951A |
| 廠商： | Semtech Corporation |
| 英文描述： | 150mA Adjustable Voltage Regulators(低壓差，5V固定輸出或可調(diào)輸出(1.24-29V)，150mA穩(wěn)壓器) |
| 中文描述： | 150mA的可調(diào)穩(wěn)壓器（低壓差，5V的固定輸出或可調(diào)輸出（1.24 - 29V），150mA的穩(wěn)壓器） |
| 文件頁數(shù)： | 5/7頁 |
| 文件大小： | 175K |
| 代理商： | LP2951A |
5
2001 Semtech Corp.
www.semtech.com
LP2951A
POWER MANAGEMENT
Setting the Output Voltage
The LP2951(A) can be set to deliver any output voltage
from 1.24V to 30V by using an external voltage divider.
In addition, an internal voltage divider is provided if a 5V
(or 3.3V for LP2951-3.3) output is desired. To use the
internal voltage divider, simply connect the sense pin to
the output and the tap pin to the feedback pin (see block
diagram). When using an external divider the sense and
tap pins are left open, and the divider is installed from
the output to ground, with its center connected to the
feedback pin (see Adjustable Regulator figure below).
When using an external voltage divider, resistances can
be calculated from the following formula:
V
OUT =
V
235
.
1
R
x
10
x
20
2
R
235
.
1
9
+
+
An upper limit of values for R2 occurs at ~1.2MW if the
regulator is to be operated when completely unloaded,
as this allows the feedback divider to provide the 1A
minimum load recommended for the LP2951(A). If the
regulator always has a load of 1A or more connected
externally, higher resistor values can be used, but
attention must be paid to the -20nA (typical) bias current
required by the feedback pin. Using a 1.2MW resistor for
R2, this bias current will already cause a 2% shift in
output voltage between full load and no load. Larger
values of R2 exacerbate the problem. Using a 120kW
resistor for R2 reduces the error caused by feedback
bias current to 0.2% while still only requiring 10A to
feed the divider string.
Output Filtering
An output filter capacitor is always necessary with the
LP2951(A) in order to assure output stability. The size of
this capacitor varies with output voltage (smaller at higher
output voltages) and output current (smaller at lower
output currents). For 5V operation 1F is sufficient. For
regulator operation at minimum output voltage (1.24V)
and output currents of 100mA, the required filter
increases to 3.3F. Any type of capacitor may be used,
although if aluminum electrolytics are chosen, the equiva-
lent series resistance (ESR) should be held to 5W or less.
For small load currents the capacitance can be reduced.
0.33F will be satisfactory for output currents of 10mA
or less, and 0.1F will work if output current is below
1mA.
Theoretically, it is also possible for the regulator to
become unstable if very large capacitances (>10,000F)
are connected to the output, but this has not been
observed in practice. It is also important that the
capacitance be mounted close (1cm or less) to the
output pin of the regulator.
Figure 1: Adjustable Regulator
If the lead inductance between the input of the
LP2951(A) and its power source exceeds ~500nH
(approximately 10/25cm of 0.031/0.78mm trace) it
may also be necessary to add a filter capacitor between
the input terminal and ground. A 1F tantalum or
aluminum electrolytic capacitor is usually sufficient. Lower
values can be used if load currents are small. Noise
injection into the feedback terminal of the LP2951(A)
from nearby noise sources can also upset the output.
Generally this can be cured by the addition of 100pF or
so from the feedback terminal to the output.
Reducing Output Noise
In ultra-quiet systems, or when the LP2951(A) is being
used as a reference, it may be desirable to perform
additional output filtering to reduce noise. While this can
be done by simply using larger capacitors on the output,
that solution tends to be bulky and expensive, and even-
tually, with huge capacitors (>1,000F) may cause
instability in the regulator. Generally, it is more cost-
effective to let the regulator regulate output noise away.
Applications Information (LP2951(A))
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LP2951AC | 制造商:Alpha & Omega Semiconductor 功能描述: 制造商:Alpha & Omega Semiconductor 功能描述:Electronic Component |
| LP2951ACD | 功能描述:低壓差穩(wěn)壓器 - LDO 1.23-30V or 5V 100mA 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(dòng)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 |
| LP2951ACD3.0 | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:100 mA, Low Power Low Dropout Voltage Regulator |
| LP2951ACD-3.0 | 功能描述:低壓差穩(wěn)壓器 - LDO 3V 100mA Low Power 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(dòng)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 |
| LP2951ACD-3.0G | 功能描述:低壓差穩(wěn)壓器 - LDO 3V 100mA Low Power w/Error Flag Output 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(dòng)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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