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參數(shù)資料
| 型號(hào)： | LP3987 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Micropower micro SMD 150 mA Ultra Low-Dropout CMOS Voltage Regulators with sleep MODE |
| 中文描述： | 微微型SMD一百五十零毫安超低壓差CMOS電壓調(diào)節(jié)器，睡眠模式 |
| 文件頁(yè)數(shù)： | 14/17頁(yè) |
| 文件大?。?/td> | 533K |
| 代理商： | LP3987 |
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Application Hints
EXTERNAL CAPACITORS
Like any low-dropout regulator, the LP3987 requires external
capacitors for regulator stability. The LP3987 is specifically
designed for portable applications requiring minimum board
space and smallest components. These capacitors must be
correctly selected for good performance.
INPUT CAPACITOR
An input capacitance of
)
1μF is required between the
LP3987 input pin and ground (the amount of the capacitance
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 analog
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 on the input capaci-
tor, but tolerance and temperature coefficient must be con-
sidered when selecting the capacitor to ensure the capaci-
tance will be
)
1μF over the entire operating temperature
range.
OUTPUT CAPACITOR
The LP3987 is designed specifically to work with very small
ceramic output capacitors. A ceramic capacitor (dielectric
types Z5U, Y5V or X7R) in 1 to 4.7 μF range with 5m
to
500m
ESR range is suitable in the LP3987 application
circuit.
It may also be possible to use tantalum or film capacitors at
the output, but these are not as attractive for reasons of size
and cost (see next section Capacitor Characteristics).
The output capacitor must meet the requirement for mini-
mum amount of capacitance and also have an ESR (Equiva-
lent Series Resistance) value which is within a stable range
(5 m
to 500 m
).
NO-LOAD STABILITY
The LP3987 will remain stable and in regulation with no
external load. This is specially important in CMOS RAM
keep-alive applications.
CAPACITOR CHARACTERISTICS
The LP3987 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 1μF to 4.7μF range,
ceramic capacitors are the smallest, least expensive and
have the lowest ESR values (which makes them best for
eliminating high frequency noise). The ESR of a typical 1μF
ceramic capacitor is in the range of 20 m
to 40 m
, which
easily meets the ESR requirement for stability by the
LP3987. The ceramic capacitor’s capacitance can vary with
temperature. Most large value ceramic capacitors (
)
2.2μF)
are manufactured with Z5U or Y5V temperature characteris-
tics, which results in the capacitance dropping by more than
50% as the temperature goes from 25C to 85C.
A better choice for temperature coefficient in a ceramic
capacitor is X7R, which holds the capacitance within
±
15%.
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.
ON/OFF INPUT OPERATION
The LP3987 is turned off by pulling the V
pin low, and
turned on by pulling it high. If this feature is not used, the V
pin should be tied to V
to keep the regulator output on at all
time. To assure proper operation, the signal source used to
drive the V
input must be able to swing above and below
the specified turn-on/off voltage thresholds listed in the Elec-
trical Characteristics section under V
IL
and V
IH
.
MODE OPERATION
The LP3987 enters sleep mode by pulling MODE = 0V
externally to reduce current during standby operation. During
sleep mode, LP3987 consumes only 14μA of quiescent cur-
rent and supplies up to 3mA of current. The device returns to
active mode by pulling MODE = 1.8V. If this function is not
used, the MODE pin should be tied to V
IN
.
THERMAL PROTECTION
The LP3987 has internal thermal protection circuitry to dis-
able the internal pass transistor if the junction temperature
exceeds 125C to allow the device to cool down. The pass
transistor will turn on when temperature falls below the maxi-
mum operating junction temperature of 125C. This feature
is designed to protect the device in the event of fault condi-
tions. For normal operation, it is suggested to limit the device
junction temperature to less than 125C.
MICRO SMD MOUNTING
The micro SMD package requires specific mounting tech-
niques which are detailed in National Semiconductor Appli-
cation Note (AN-1112). Referring to the section
Surface
Mount Technology (SMT) Assembly Considerations
, it
should be noted that the pad style which must be used with
the 5 pin package is NSMD (non-solder mask defined) type.
For best results during assembly, alignment ordinals on the
PC board may be used to facilitate placement of the micro
SMD device.
MICRO SMD LIGHT SENSITIVITY
Exposing the micro SMD device to direct sunlight will cause
misoperation of the device. Light sources such as Halogen
lamps can effect electrical performance if brought near to the
device. The wavelengths which have most detrimental effect
are reds and infra-reds, which means that the fluorescent
lighting used inside most buildings has very little effect on
performance. A micro SMD test board was brought to within
1cm of a fluorescent desk lamp and the effect on the regu-
lated output voltage was negligible, showing a deviation of
less than 0.1% from nominal.
L
www.national.com
14
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PDF描述 |
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| LP3988ITL-2.85 | Micropower, 150mA Ultra Low-Dropout CMOS Voltage Regulator With Power Good |
| LP3988ITLX-1.85 | Micropower, 150mA Ultra Low-Dropout CMOS Voltage Regulator With Power Good |
| LP3988ITLX-2.6 | Micropower, 150mA Ultra Low-Dropout CMOS Voltage Regulator With Power Good |
| LP3988ITLX-2.85 | Micropower, 150mA Ultra Low-Dropout CMOS Voltage Regulator With Power Good |
| LP3988IMFX-2.5 | Micropower, 150mA Ultra Low-Dropout CMOS Voltage Regulator With Power Good |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LP3987-1.5B3A | 制造商:POWER 制造商全稱:Lowpower Semiconductor inc 功能描述:300mA,Ultra-LowNoise Ultra-fast CMOS LDO Regrlator |
| LP3987-1.5B3B | 制造商:POWER 制造商全稱:Lowpower Semiconductor inc 功能描述:300mA,Ultra-LowNoise Ultra-fast CMOS LDO Regrlator |
| LP3987-1.5B3C | 制造商:POWER 制造商全稱:Lowpower Semiconductor inc 功能描述:300mA,Ultra-LowNoise Ultra-fast CMOS LDO Regrlator |
| LP3987-1.5B3D | 制造商:POWER 制造商全稱:Lowpower Semiconductor inc 功能描述:300mA,Ultra-LowNoise Ultra-fast CMOS LDO Regrlator |
| LP3987-1.5B3E | 制造商:POWER 制造商全稱:Lowpower Semiconductor inc 功能描述:300mA,Ultra-LowNoise Ultra-fast CMOS LDO Regrlator |
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