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PDF LX8415-00CST Data sheet ( Hoja de datos )
| Número de pieza | LX8415-00CST | |
| Descripción | 0.5 A LOW DROPOUT POSITIVE REGULATORS | |
| Fabricantes | Microsemi Corporation | |
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T H E I N F I N I T E P O W E R O F I N N O VAT I O N
L I N D O C #: 8415
LX8415-xx
0.5A LOW DROPOUT POSITIVE REGULATORS
PR E L I M I N A RY D ATA S H E E T
DESCRIPTION
The LX8415 series ICs are positive Low
Dropout (LDO) regulators. At the de-
signed maximum load current, the
LX8415 series dropout voltage is guar-
anteed to be 1.3V or lower at 0.5A. The
dropout voltage decreases with load
current.
The LX8415 is available in an adjust-
able output voltage version and fixed
output versions of 2.5V and 3.3V. On-
chip trimming of the internal voltage
reference allows specification of the
initial output voltage to within ±1% of
its nominal value. The output current-
limit point is also trimmed, which helps
to minimize stress on both the regulator
and the system power source when they
are operated under short-circuit condi-
tions. The regulator's internal circuitry
will operate at input-to-output differen-
tial voltages down to 1V.
Most regulator circuit designs include
output capacitors with values in the
range of tens to hundreds of microfarads
or more. The LX8415 typically requires
at least 10µF of output capacitance for
stable operation.
The LX8415 is available in the low-
profile plastic SOT-223 package for ap-
plications where space is at a premium.
NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.
PRODUCT HIGHLIGHT
LOW COST 5V TO 3.3V REGULATOR
VIN
LX8415-xx
IN OUT
VOUT
5V
ADJ
3.3V
R1
10µF
60.4Ω
22µF
R2
100Ω
KEY FEATURES
s 0.7% Line Regulation Maximum
s 0.7% Load Regulation Maximum
s Output Current Of 500mA
s Regulates To <1.3V Dropout
s Space Saving SOT-223 Surface
Mount Package
s Guaranteed Dropout Voltage At Multiple
Current Levels
s 3-Terminal Adjustable, Fixed 2.5V And
Fixed 3.3V
A P P L I C AT I O N S
s Battery Chargers
s 5V To 3.3V Linear Regulators
s Post Regulators For Switching Supplies
s Modems
s DVD Players
A VA I L A B L E O PTIONS P E R P A RT #
Part #
Output
Voltage
LX8415-25
2.5V
LX8415-33
3.3V
LX8415-00
Adjustable
Copyright © 1999
Rev. 0.4 1/99
PA CKA GE OR D E R INFO
TA (°C)
ST
Plastic
3-pin
SOT-223
0 to 125
LX8415-xxCST
Note: All surface-mount packages are available in Tape & Reel.
Append the letter "T" to part number (i.e. LX8415-33CSTT).
"xx" refers to output voltage, please see table above.
LINFINITY MICROELECTRONICS INC.
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
1
1 page  
PRODUCT DATABOOK 1996/1997
0.5A LOW DROPOUT POSITIVE REGULATORS
PR E L I M I N A RY D ATA S H E E T
LX8415-xx
APPLICATION NOTES
OUTPUT VOLTAGE
The LX8415 ICs develop a 1.25V reference voltage between the output
and the adjust terminal (See Figure 2). By placing a resistor, R1,
between these two terminals, a constant current is caused to flow
through R1 and down through R2 to set the overall output voltage.
Normally this current is the specified minimum load current of 10mA.
Because IADJis very small and constant when compared with the current
through R1, it represents a small error and can usually be ignored.
LX8415-xx
VIN IN OUT
ADJ
VREF
IADJ
50µA
VOUT = VREF
1
+
R2
R1
+ IADJ R2
VOUT
R1
R2
FIGURE 2 — BASIC ADJUSTABLE REGULATOR
LOAD REGULATION
Because the LX8415 regulators are three-terminal devices, it is not
possible to provide true remote load sensing. Load regulation will
be limited by the resistance of the wire connecting the regulator to
the load. The data sheet specification for load regulation is
measured at the bottom of the package. Negative side sensing is a
true Kelvin connection, with the bottom of the output divider
returned to the negative side of the load. Although it may not be
immediately obvious, best load regulation is obtained when the top
of the resistor divider, (R1), is connected directly to the case of the
regulator, not to the load. This is illustrated in Figure 3. If R1 were
connected to the load, the effective resistance between the regulator
and the load would be:
RPeff
=
RP
*
R2+R1
R1
where: RP ≡ Actual parasitic line resistance.
When the circuit is connected as shown in Figure 3, the parasitic
resistance appears as its actual value, rather than the higher RPeff.
Even when the circuit is optimally configured, parasitic resistance
can be a significant source of error. A 100 mil (2.54 mm) wide PC
trace built from 1 oz. copper-clad circuit board material has a
parasitic resistance of about 5 milliohms per inch of its length at
room temperature. If a 3-terminal regulator used to supply 2.50 volts
is connected by 2 inches of this trace to a load which draws 5 amps
of current, a 50 millivolt drop will appear between the regulator and
the load. Even when the regulator output voltage is precisely
2.50 volts, the load will only see 2.45 volts, which is a 2% error. It
LOAD REGULATION (continued)
LX8415-xx
ParRaPsitic
Line Resistance
VIN IN
OUT
ADJ Connect
R1 to Case
of Regulator
R1
R2
RL
Connect
R2
to Load
FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION
is important to keep the connection between the regulator output
pin and the load as short as possible, and to use wide traces or
heavy-gauge wire.
The minimum specified output capacitance for the regulator
should be located near the reglator package. If several capacitors
are used in parallel to construct the power system output capaci-
tance, any capacitors beyond the minimum needed to meet the
specified requirements of the regulator should be located near the
sections of the load that require rapidly-changing amounts of
current. Placing capacitors near the sources of load transients will
help ensure that power system transient response is not impaired
by the effects of trace impedance.
To maintain good load regulation, wide traces should be used on
the input side of the regulator, especially between the input
capacitors and the regulator. Input capacitor ESR must be small
enough that the voltage at the input pin does not drop below VIN (MIN)
during transients.
V = V + VIN (MIN)
OUT DROPOUT (MAX)
where:
VIN (MIN)
≡ the lowest allowable instantaneous
voltage at the input pin.
VOUT ≡ the designed output voltage for the
power supply system.
VDROPOUT (MAX) ≡ the specified dropout voltage
for the installed regulator.
THERMAL CONSIDERATIONS
The LX8415 regulators have internal power and thermal limiting
circuitry designed to protect each device under overload conditions.
For continuous normal load conditions, however, maximum junc-
tion temperature ratings must not be exceeded. It is important to
give careful consideration to all sources of thermal resistance from
junction to ambient. This includes junction to case, case to heat sink
interface, and heat sink thermal resistance itself.
Copyright © 1999
Rev. 0.4 1/99
5
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