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PDF LP3876ET-5.0 Data sheet ( Hoja de datos )
| Número de pieza | LP3876ET-5.0 | |
| Descripción | 3A Fast Ultra Low Dropout Linear Regulators | |
| Fabricantes | National Semiconductor | |
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September 2003
LP3873/LP3876
3A Fast Ultra Low Dropout Linear Regulators
General Description
The LP3873/LP3876 series of fast ultra low-dropout linear
regulators operate from a +2.5V to +7.0V input supply. Wide
range of preset output voltage options are available. These
ultra low dropout linear regulators respond very quickly to
step changes in load, which makes them suitable for low
voltage microprocessor applications. The LP3873/LP3876
are developed on a CMOS process which allows low quies-
cent current operation independent of output load current.
This CMOS process also allows the LP3873/LP3876 to op-
erate under extremely low dropout conditions.
Dropout Voltage: Ultra low dropout voltage; typically 80mV
at 300mA load current and 800mV at 3A load current.
Ground Pin Current: Typically 6mA at 3A load current.
Shutdown Mode: Typically 1µA quiescent current when the
shutdown pin is pulled low.
Error Flag: Error flag goes low when the output voltage
drops 10% below nominal value.
SENSE: Sense pin improves regulation at remote loads.
Precision Output Voltage: Multiple output voltage options
are available ranging from 1.8V to 5.0V with a guaranteed
accuracy of ±1.5% at room temperature, and ±3.0% over all
conditions (varying line, load, and temperature).
Features
n Ultra low dropout voltage
n Low ground pin current
n Load regulation of 0.08%
n 1µA quiescent current in shutdown mode
n Guaranteed output current of 3A DC
n Available in TO-263 and TO-220 packages
n Output voltage accuracy ± 1.5%
n Error flag indicates output status
n Sense option improves load regulation
n Minimum output capacitor requirements
n Overtemperature/overcurrent protection
n −40˚C to +125˚C junction temperature range
Applications
n Microprocessor power supplies
n GTL, GTL+, BTL, and SSTL bus terminators
n Power supplies for DSPs
n SCSI terminator
n Post regulators
n High efficiency linear regulators
n Battery chargers
n Other battery powered applications
Typical Application Circuits
20060501
*SD and ERROR pins must be pulled high through a 10kΩ pull-up resistor. Connect the ERROR pin to ground if this function is not used. See application hints
for more information.
© 2003 National Semiconductor Corporation DS200605
www.national.com
1 page  
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Storage Temperature Range
Lead Temperature
(Soldering, 5 sec.)
ESD Rating (Note 3)
Power Dissipation (Note 2)
Input Supply Voltage (Survival)
Shutdown Input Voltage
(Survival)
Output Voltage (Survival), (Note
6), (Note 7)
−65˚C to +150˚C
260˚C
2 kV
Internally Limited
−0.3V to +7.5V
−0.3V to 7.5V
−0.3V to +6.0V
IOUT (Survival)
Short Circuit Protected
Maximum Voltage for ERROR
Pin VIN
Maximum Voltage for SENSE Pin
VOUT
Operating Ratings
Input Supply Voltage (Note 11)
Shutdown Input Voltage
Maximum Operating Current (DC)
Junction Temperature
2.5V to 7.0V
−0.3V to 7.0V
3A
−40˚C to +125˚C
Electrical Characteristics
LP3873/LP3876
Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range.
Unless otherwise specified: VIN = VO(NOM) + 1.5V, IL = 10 mA, COUT = 10µF, VSD = 2V.
Symbol
Parameter
Conditions
Typ
LP3873/6 (Note 5)
Units
(Note 4)
Min
Max
Output Voltage
VO Tolerance
(Note 8)
VOUT +1.5V ≤ VIN ≤ 7.0V
10 mA ≤ IL ≤ 3A
-1.5 +1.5
0%
-3.0 +3.0
∆V OL
Output Voltage Line
Regulation (Note 8)
VOUT + 1.5V ≤ VIN ≤ 7.0V
0.02
0.06
%
∆VO/ ∆IOUT
Output Voltage Load
Regulation
10 mA ≤ IL ≤ 3A
0.08
0.14
%
(Note 8)
VIN - VOUT
IL = 300 mA 80 100
Dropout Voltage
(Note 10)
IL = 3A
120
mV
800 1000
1200
IGND
Ground Pin Current In
Normal Operation
Mode
IL = 300 mA
IL = 3A
5
6
9
10
mA
14
15
IGND
Ground Pin Current In
Shutdown Mode
IO(PK)
Peak Output Current
SHORT CIRCUIT PROTECTION
VSD ≤ 0.3V
-40˚C ≤TJ ≤ 85˚C
VO ≥ VO(NOM) - 4%
1
4.5
10 µA
50
A
ISC Short Circuit Current
6A
5 www.national.com
5 Page 
Application Hints
VIN RESTRICTIONS FOR PROPER START-UP
To prevent misoperation, ensure that VIN is below 50mV
before start-up is initiated. This scenario can occur in sys-
tems with a backup battery using reverse-biased "blocking"
diodes which may allow enough leakage current to flow into
the VIN node to raise it’s voltage slightly above ground when
the main power is removed. Using low leakage diodes or a
resistive pull down can prevent the voltage at VIN from rising
above 50mV. Large bulk capacitors connected to VIN may
also cause a start-up problem if they do not discharge fully
before re-start is initiated (but only if VIN is allowed to fall
below 1V). A resistor connected across the capacitor will
allow it to discharge more quickly. It should be noted that the
probability of a "false start" caused by incorrect logic states
is extremely low.
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 of at least 1µF is
required. Ceramic or Tantalum may be used, and capaci-
tance may be increased without limit
OUTPUT CAPACITOR: An output capacitor is required for
loop stability. It must be located less than 1 cm from the
device and connected directly to the output and ground pins
using traces which have no other currents flowing through
them (see PCB Layout section).
The minimum value of the output capacitance that can be
used for stable full-load operation is 10 µF, but it may be
increased without limit. The output capacitor must have an
ESR value as shown in the stable region of the curve (be-
low).
ESR Curve
20060570
SELECTING A CAPACITOR
It is important to note that capacitance tolerance and varia-
tion with temperature must be taken into consideration when
selecting a capacitor so that the minimum required amount
of capacitance is provided over the full operating tempera-
ture range. In general, a good Tantalum capacitor will show
very little capacitance variation with temperature, but a ce-
ramic may not be as good (depending on dielectric type).
Aluminum electrolytics also typically have large temperature
variation of capacitance value.
Equally important to consider is a capacitor’s ESR change
with temperature: this is not an issue with ceramics, as their
ESR is extremely low. However, it is very important in Tan-
talum and aluminum electrolytic capacitors. Both show in-
creasing ESR at colder temperatures, but the increase in
aluminum electrolytic capacitors is so severe they may not
be feasible for some applications (see Capacitor Character-
istics Section).
CAPACITOR CHARACTERISTICS
CERAMIC: For values of capacitance in the 10 to 100 µF
range, ceramics are usually larger and more costly than
tantalums but give superior AC performance for bypassing
high frequency noise because of very low ESR (typically less
than 10 mΩ). However, some dielectric types do not have
good capacitance characteristics as a function of voltage
and temperature.
Z5U and Y5V dielectric ceramics have capacitance that
drops severely with applied voltage. A typical Z5U or Y5V
capacitor can lose 60% of its rated capacitance with half of
the rated voltage applied to it. The Z5U and Y5V also exhibit
a severe temperature effect, losing more than 50% of nomi-
nal capacitance at high and low limits of the temperature
range.
X7R and X5R dielectric ceramic capacitors are strongly rec-
ommended if ceramics are used, as they typically maintain a
capacitance range within ±20% of nominal over full operat-
ing ratings of temperature and voltage. Of course, they are
typically larger and more costly than Z5U/Y5U types for a
given voltage and capacitance.
TANTALUM: Solid Tantalum capacitors are recommended
for use on the output because their typical ESR is very close
to the ideal value required for loop compensation. They also
work well as input capacitors if selected to meet the ESR
requirements previously listed.
Tantalums also have good temperature stability: a good
quality Tantalum will typically show a capacitance value that
varies less than 10-15% across the full temperature range of
125˚C to −40˚C. ESR will vary only about 2X going from the
high to low temperature limits.
The increasing ESR at lower temperatures can cause oscil-
lations when marginal quality capacitors are used (if the ESR
of the capacitor is near the upper limit of the stability range at
room temperature).
ALUMINUM: This capacitor type offers the most capaci-
tance for the money. The disadvantages are that they are
larger in physical size, not widely available in surface mount,
and have poor AC performance (especially at higher fre-
quencies) due to higher ESR and ESL.
Compared by size, the ESR of an aluminum electrolytic is
higher than either Tantalum or ceramic, and it also varies
greatly with temperature. A typical aluminum electrolytic can
exhibit an ESR increase of as much as 50X when going from
25˚C down to −40˚C.
It should also be noted that many aluminum electrolytics only
specify impedance at a frequency of 120 Hz, which indicates
they have poor high frequency performance. Only aluminum
electrolytics that have an impedance specified at a higher
frequency (between 20 kHz and 100 kHz) should be used for
the LP387X. Derating must be applied to the manufacturer’s
ESR specification, since it is typically only valid at room
temperature.
11 www.national.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LP3876ET-5.0.PDF ] | |
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