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參數(shù)資料
| 型號： | LP3883 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 3A Fast-Response Ultra Low Dropout Linear Regulators |
| 中文描述： | 第3A快速反應(yīng)超低壓差線性穩(wěn)壓器 |
| 文件頁數(shù)： | 9/12頁 |
| 文件大?。?/td> | 367K |
| 代理商： | LP3883 |
Application Hints
(Continued)
F
p
= 1 / (2 X
π
X 5 X .047 X 10E-6) = 677 kHz
This pole would add close to 60 degrees of phase lag at the
crossover (unity gain) frequency of 1 MHz, which would
almost certainly make this regulator oscillate. Depending on
the load current, output voltage, and bandwidth, there are
usually values of small capacitors which can seriously re-
duce phase margin. If the capacitors are ceramic, they tend
to oscillate more easily because they have very little internal
inductance to damp it out. If bypass capacitors are used, it is
best to place them near the load and use trace inductance to
"decouple" them from the regulator output.
INPUT CAPACITOR
The input capacitor must be at least 4.7 μF, but can be
increased without limit. It’s purpose is to provide a low
source impedance for the regulator input. Ceramic capaci-
tors work best for this, but Tantalums are also very good.
There is no ESR limitation on the input capacitor (the lower,
the better). Aluminum electrolytics can be used, but their
ESR increase very quickly at cold temperatures. They are
not recommended for any application where temperatures
go below about 10C.
BIAS CAPACITOR
The 0.1μF capacitor on the bias line can be any good quality
capacitor (ceramic is recommended).
BIAS VOLTAGE
The bias voltage is an external voltage rail required to get
gate drive for the N-FET pass transistor. Bias voltage must
be in the range of 4.5 - 6V to assure proper operation of the
part.
UNDER VOLTAGE LOCKOUT
The bias voltage is monitored by a circuit which prevents the
regulator output from turning on if the bias voltage is below
approximately 4V.
SHUTDOWN OPERATION
Pulling down the shutdown (S/D) pin will turn-off the regula-
tor. Pin S/D must be actively terminated through a pull-up
resistor (10 k
to 100 k
) for a proper operation. If this pin
is driven from a source that actively pulls high and low (such
as a CMOS rail to rail comparator), the pull-up resistor is not
required. This pin must be tied to Vin if not used.
POWER DISSIPATION/HEATSINKING
A heatsink may be required depending on the maximum
power dissipation and maximum ambient temperature of the
application. Under all possible conditions, the junction tem-
perature must be within the range specified under operating
conditions. The total power dissipation of the device is given
by:
P
D
= (V
IN
V
OUT
)I
OUT
+ (V
IN
)I
GND
where I
GND
is the operating ground current of the device.
The maximum allowable temperature rise (T
Rmax
) depends
on the maximum ambient temperature (T
Amax
) of the appli-
cation, and the maximum allowable junction temperature
(T
Jmax
):
T
Rmax
= T
Jmax
T
Amax
The maximum allowable value for junction to ambient Ther-
mal Resistance,
θ
JA
, can be calculated using the formula:
θ
JA
= T
Rmax
/ P
D
These parts are available in TO-220 and TO-263 packages.
The thermal resistance depends on amount of copper area
or heat sink, and on air flow. If the maximum allowable value
of
θ
JA
calculated above is
≥
60 C/W for TO-220 package
and
60 C/W for TO-263 package no heatsink is needed
since the package can dissipate enough heat to satisfy these
requirements. If the value for allowable
θ
JA
falls below these
limits, a heat sink is required.
HEATSINKING TO-220 PACKAGE
The thermal resistance of a TO220 package can be reduced
by attaching it to a heat sink or a copper plane on a PC
board. If a copper plane is to be used, the values of
θ
JA
will
be same as shown in next section for TO263 package.
The heatsink to be used in the application should have a
heatsink to ambient thermal resistance,
θ
HA
≤ θ
JA
θ
CH
θ
JC
.
In this equation,
θ
is the thermal resistance from the case
to the surface of the heat sink and
θ
is the thermal resis-
tance from the junction to the surface of the case.
θ
JC
is
about 3C/W for a TO220 package. The value for
θ
CH
de-
pends on method of attachment, insulator, etc.
θ
between 1.5C/W to 2.5C/W. If the exact value is unknown,
2C/W can be assumed.
HEATSINKING TO-263 PACKAGE
The TO-263 package uses the copper plane on the PCB as
a heatsink. The tab of these packages are soldered to the
copper plane for heat sinking. The graph below shows a
curve for the
θ
JA
of TO-263 package for different copper area
sizes, using a typical PCB with 1 ounce copper and no solder
mask over the copper area for heat sinking.
20062425
FIGURE 1.
θ
JA
vs Copper (1 Ounce) Area for TO-263
package
L
www.national.com
9
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| LP3883ES-1.2 | 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(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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| LP3883ES-1.2/NOPB | 功能描述:低壓差穩(wěn)壓器 - LDO High Performance Dual-Rail 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(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 |
| LP3883ES-1.5 | 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(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 |
| LP3883ES-1.5/NOPB | 功能描述:低壓差穩(wěn)壓器 - LDO High Performance Dual-Rail 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(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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