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PDF LP38501-ADJ Data sheet ( Hoja de datos )
| Número de pieza | LP38501-ADJ | |
| Descripción | (LP38501-ADJ / LP38503-ADJ) 3A FlexCap Low Dropout Linear Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LP38501-ADJ (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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May 19, 2008
LP38501/3-ADJ, LP38501A/3A-ADJ
3A FlexCap Low Dropout Linear Regulator for 2.7V to 5.5V
Inputs
General Description
National's FlexCap LDO's feature unique compensation that
allows the use of any type of output capacitor with no limits
on minimum or maximum ESR. The LP38501/3 series of low-
dropout linear regulators operates from a +2.7V to +5.5V input
supply. These ultra low dropout linear regulators respond very
quickly to step changes in load, which makes them suitable
for low voltage microprocessor applications. Developed on a
CMOS process, (utilizing a PMOS pass transistor), the
LP38501/3 has low quiescent current that changes little with
load current.
Ground Pin Current: Typically 2 mA at 3A load current.
Disable Mode: Typically 25 nA quiescent current when the
Enable pin is pulled low.
Simplified Compensation: Stable with any type of output
capacitor, regardless of ESR.
Precision Output: "A" grade versions available with 1.5%
VADJ tolerance (25°C) and 3% over line, load and tempera-
ture.
Features
■ FlexCap: Stable with ceramic, tantalum, or aluminum
capacitors
■ Stable with 10 µF input/output capacitor
■ Adjustable output voltage from 0.6V to 5V
■ Low ground pin current
■ 25 nA quiescent current in shutdown mode
■ Guaranteed output current of 3A
■ Available in TO-263, TO-263 THIN packages
■ Guaranteed VADJ accuracy of ±1.5% @ 25°C (A Grade)
■ Guaranteed VADJ accuracy of ±3.5% @ 25°C (STD)
■ Over-Temperature and Over-Current protection
■ −40°C to +125°C operating TJ range
■ Enable pin (LP38501)
Applications
■ ASIC Power Supplies In:
Printers, Graphics Cards, DVD Players
Set Top Boxes, Copiers, Routers
■ DSP and FPGA Power Supplies
■ SMPS Regulatorwww.DataSheet.co.kr
■ Conversion from 3.3V or 5V Rail
Typical Application Circuit
© 2008 National Semiconductor Corporation 300281
30028119
www.national.com
Datasheet pdf - http://www.DataSheet4U.net/
1 page  
Symbol
Parameter
Conditions
Min Typ Max Units
AC Parameters
PSRR Ripple Rejection
VIN = 3.0V, IOUT = 3A
f = 120Hz
VIN = 3.0V, IOUT = 3A
f = 1 kHz
— 58 —
dB
— 56 —
ρn(l/f)
Output Noise Density
en Output Noise Voltage
Thermal Characteristics
f = 120Hz, COUT = 10 µF CER
BW = 100Hz – 100kHz
COUT = 10 µF CER
— 1.0 — µV/√Hz
— 100 — µV (rms)
TSD
ΔTSD
Thermal Shutdown
TJ rising
Thermal Shutdown Hysteresis TJ falling from TSD
— 170 —
— 10 —
°C
Thermal Resistance
θJ-A Junction to Ambient
Thermal Resistance
θJ-C Junction to Case
TO-263, TO-263 THIN(Note 8)
1 sq. in. copper
37
°C/W
TO-263, TO-263 THIN
—5—
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but does not guarantee specific performance limits. For guaranteed specifications and conditions, see the Electrical Characteristics.
Note 2: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.
Note 3: Operating junction temperature must be evaluated, and derated as needed, based on ambient temperature (TA), power dissipation (PD), maximum
allowable operating junction temperature (TJ(MAX)), and package thermal resistance (θJA). See Application Information.
Note 4: Output voltage line regulation is defined as the change in output voltage from the nominal value due to change in the voltage at the input.
Note 5: Output voltage load regulation is defined as the change in output voltage from the nominal value due to change in the load current at the output.
Note 6: The line and load regulation specification contains only the typical number. However, the limits for line and load regulation are included in the output
voltage tolerance specification.
Note 7: Dropout voltage is defined as the minimum input to output differential voltage at which the output drops 2% below the nominal value. For any output
voltage less than 2.5V, the minimum VIN operating voltage is the limiting factor.
Note 8: The value of θJA for the TO-263 (TS) package and TO-263 THIN (TJ) package can range from approximately 30 to 60°C/W depending on the amount of
PCB copper dedicated to heat transfer (See Application Information).
www.DataSheet.co.kr
5 www.national.com
Datasheet pdf - http://www.DataSheet4U.net/
5 Page 
30028135
FIGURE 6. Rising Edge, 10 µF Ceramic, 75A/µs di/dt
It can be seen from the figure that the output voltage starts
“correcting” back upwards after less than a micro second, and
has fully reversed direction after about 1.2 µs. This very rapid
reaction is a result of the maximum loop bandwidth (full load
is being delivered) and the feedforward effect kicking on the
drive to the FET before feedback gets fully around the loop.
In cases where extremely fast load changes occur, and output
voltage regulation better than 10% is required, the output ca-
pacitance must be increased. When selecting capacitors, it
must be understood that the better performing ones usually
cost the most. For fast changing loads, the internal parasitics
of ESR (equivalent series resistance) and ESL (equivalent
series inductance) degrade the capacitor’s ability to source
current quickly to the load. The best capacitor types for tran-
sient performance are (in order):
1. Multilayer Ceramic: with the lowest values of ESR and
ESL, they can have ESR values in the range of a few milli
Ohms. Disadvantage: capacitance values above about
22 µF significantly increase in cost.
2. Low-ESR Aluminum Electrolytics: these are aluminum
types (like OSCON) with a special electrolyte which
provides extremely low ESR values, and are the closest
to ceramic performance while still providing large
amounts of capacitance. These are cheaper (by
capacitance) than ceramic.
3. Solid tantalum: can provide several hundred µF of
capacitance, transient performance is slightly worse than
OSCON type capacitors, cheaper than ceramic in large
values.
4. General purpose aluminum electrolytics: cheap and
provide a lot of capacitance, but give the worst
performance.
As a first example, larger values of ceramic capacitance will
be tried to show how much reduction can be obtained from
the 200 mV output change (Figure 6) which was seen with
only a 10 µF ceramic output capacitor. In Figure 7, the 10 µF
output capacitor is increased to 22 µF. The 200 mV transient
is reduced to about 160 mV, which is from about 11% of
VOUT down to about 9%.
30028137
FIGURE 7. 22 µF Ceramic Output Capacitor
In Figure 8, the output capacitance is increased to 47 µF ce-
ramic. It can be seen that the output transient is further
reduced down to about 120 mV, which is still about 6.6% of
the output voltage. This shows that a 5X increase in ceramic
capacitance from the original 10 µF only reduced the peak
voltage transient amplitude by about 40%.
www.DataSheet.co.kr
30028138
FIGURE 8. 47 µF Ceramic Output Capacitor
In general, managing load transients is done by paralleling
ceramic capacitance with a larger bulk capacitance. In this
way, the ceramic can source current during the rapidly chang-
ing edge and the bulk capacitor can support the load current
after the first initial spike in current.
In the next test, the same 10 µF ceramic capacitor will be
paralleled with a general purpose (cheap) aluminum elec-
trolytic whose capacitance is 220 µF. As shown in Figure 9,
there is a small improvement over the 200 mV peak seen with
the 10 µF ceramic alone. By adding the 220 µF aluminum
capacitor, the peak is reduced to about 160 mV (the same
peak value as seen with a 22 µF ceramic capacitor alone).
11
www.national.com
Datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
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| PDF Descargar | [ Datasheet LP38501-ADJ.PDF ] | |
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