Page 1
LIN DOC #:
V
8415
LX8415-xx
0.5A LOW DROPOUT POSITIVE REGULATORS
T HE I NFINITE P OWER OF I NNOVATION
DESCRIPTION KEY FEATURES
The LX8415 series ICs are positive Low
Dropout (LDO) regulators. At the designed maximum load current, the
LX8415 series dropout voltage is guaranteed to be 1.3V or lower at 0.5A. The
dropout voltage decreases with load
current.
The LX8415 is available in an adjustable output voltage version and fixed
output versions of 2.5V and 3.3V. Onchip trimming of the internal voltage
reference allows specification of the
initial output voltage to within ±1% of
its nominal value. The output currentlimit point is also trimmed, which helps
NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.
PRODUCT HIGHLIGHT
to minimize stress on both the regulator
and the system power source when they
are operated under short-circuit conditions. The regulator's internal circuitry
will operate at input-to-output differential 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 lowprofile plastic SOT-223 package for applications where space is at a premium.
LOW COST 5V TO 3.3V REGULATOR
LX8415-xx
5V
IN
IN
ADJ
OUT
R
1
60.4
Ω
10µF 22µF
P RELIMINARY DATA SHEET
■ 0.7% Line Regulation Maximum
■ 0.7% Load Regulation Maximum
■ Output Current Of 500mA
■ Regulates To <1.3V Dropout
■ Space Saving SOT-223 Surface
Mount Package
■ Guaranteed Dropout Voltage At Multiple
Current Levels
■ 3-Terminal Adjustable, Fixed 2.5V And
Fixed 3.3V
APPLICATIONS
■ Battery Chargers
■ 5V To 3.3V Linear Regulators
■ Post Regulators For Switching Supplies
■ Modems
■ DVD Players
AVAILABLE OPTIONS PER PART #
V
OUT
3.3V
Part #
LX8415-25 2.5V
LX8415-33 3.3V
LX8415-00 Adjustable
Voltage
Output
R
2
100
Ω
PACKAGE ORDER INFO
(°C)
T
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.
Copyright © 1999
Rev. 0.4 1/99
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
L INF INITY MICROELECTRONICS INC.
A
0 to 125 LX8415-xxCST
Plastic SOT-223
ST
3-pin
1
Page 2
LX8415-xx
T
A
PRODUCT DATABOOK 1996/1997
0.5A LOW DROPOUT POSITIVE REGULATORS
RELIMINARY DATA SHEET
P
ABSOLUTE MAXIMUM RATINGS (Note 1)
Power Dissipation .................................................................................. Internally Limited
Input Voltage
LX8415-00 (Adjustable) / 8415-33 (3.3V) .................................................................. 7V
Surge Voltage ................................................................................................................. 7V
Operating Junction Temperature
Plastic (ST, DD & DT Packages) .......................................................................... 150°C
Storage Temperature Range ...................................................................... -65°C to 150°C
Lead Temperature (Soldering, 10 seconds) ............................................................. 300°C
Short-Circuit Protection ....................................................................................... Indefinite
Note 1. Exceeding these ratings could cause damage to the device. All voltages are with
respect to Ground. Currents are positive into, negative out of the specified terminal.
THERMAL DATA
ST PACKAGE:
THERMAL RESISTANCE-JUNCTION TO TAB,
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
Junction Temperature Calculation: TJ = TA + (P
thermal performance of the device/pc-board system. All of the above assume no ambient airflow.
* θ
can be improved with package soldered to 0.5IN2 copper area over backside ground
JA
plane or internal power plane. θ
mounting technique. (See Application Notes Section: Thermal Considerations)
can vary from 20ºC/W to > 40ºC/W depending on
JA
θθ
θ
θθ
JT
θθ
θ
θθ
JA
x θJA). The θ
D
15°C/W
*150°C/W
numbers are guidelines for the
JA
PACKAGE PIN OUTS
TAB IS V
OUT
3. IN
2. OUT
1. ADJ / GND
ST PACKAGE
(Top View)
V
DJ
BLOCK DIAGRAM
IN
Bias
Circuit
Thermal
Limit Circuit
Bandgap
Circuit
Control
Circuit
Output
Circuit
Current
Limit Circuit
V
OU
2
Copyright © 1999
Rev. 0.4 1/99
Page 3
PRODUCT DATABOOK 1996/1997
LX8415-xx
0.5A LOW DROPOUT POSITIVE REGULATORS
P RELIMINARY DATA SHEET
RECOMMENDED OPERATING CONDITIONS (Note 2)
Parameter
Symbol
Input Voltage
Operating Voltage LX8415-xx
Operating Ambient Temperature Range
Note 2. Range over which the device is functional.
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified: 0°C ≤ TJ ≤ 125°C, I
Parameter
Reference Voltage LX8415-00 V
Output Voltage LX8415-25 I
LX8415-33 I
Line Regulation LX8415-00 I
(Note 3) LX8415-25 / 33 I
Load Regulation LX8415-00 (VIN - V
(Note 3) LX8415-25 / 33 V
Dropout Voltage LX8415-xx I
(Note 4) I
Current Limit LX8415-xx I
Minimum Load Current (Note 5) V
Quiescent Current LX8415-25 / 33 V
Thermal Regulation TA = 25°C, 30ms Pulse
Ripple Rejection f
Adjust Pin Current LX8415(A)-00
Adjust Pin Current Change
Temperature Stability
Long Term Stability TA = 125°C, 1000Hrs
RMS Output Noise (% of V
Notes: 3. See thermal regulation specification for changes in output voltage due to heating effects. Load regulation and line regulation are measured at a constant junction
temperature by low duty cycle pulse testing.
4. Dropout voltage is specified over the full output current range of the device. Dropout voltage is defined as the minimum input/output differential measured at the
specified output current. Test points and limits are also shown on the Dropout Voltage Curve.
5. Minimum load current is defined as the minimum output current required to maintain regulation.
LX8415(A)-00 10mA ≤ I
= 0.5A for the LX8415-xx.)
MAX
Symbol
REFIOUT
OUT (MAX)(VIN
= 10mA, (VIN - V
10mA ≤ I
= 10mA, VIN = 5V, TJ = 25°C
OUT
0mA ≤ I
= 10mA, VIN = 5V, TJ = 25°C
OUT
0mA ≤ I
= 10mA, 1.5V ≤ V
OUT
= 0mA, 4.75V ≤ VIN ≤ 6V
OUT
OUT
= 4.75V, 0mA ≤ I
IN
= 100mA
OUT
= 300mA
OUT
I
= I
OUT
MAX
- V
OUT
≤ 6V, (LX8415-00)
IN
≤ 6V
IN
= 120Hz, (VIN - V
RIPPLE
Test Conditions Units
) = 2V, TJ = 25°C
OUT
≤ I
, 1.5V ≤ (V
OUT
MAX
≤ I
, 4.75V ≤ VIN ≤ 6V
OUT
MAX
≤ I
, 4.75V ≤ VIN ≤ 6V
OUT
MAX
) = 3V, 10mA ≤ I
) ≥ 1.3V, T
≤ I
OUT
), 10Hz ≤ f ≤ 10kHz
OUT
OUT
= 25°C
J
, 1.5V ≤ (V
MAX
- V
IN
≤ I
OUT
- V
IN
≤ 6V
OUT
≤ I
OUT
MAX
) = 3V, V
- V
IN
MAX
Recommended Operating Conditions
Min. Typ. Max.
0 125 °C
Min. Typ. Max.
1.238 1.250 1.262 V
OUT
RIPPLE
OUT
) ≤ 6V
) ≤ 6V
= 1Vp - p
1.225 1.250 1.275 V
2.475 2.500 2.525 V
2.450 2.500 2.550 V
3.267 3.300 3.333 V
3.235 3.300 3.365 V
500 950 mA
Units
7V
LX8415-xx
0.05 0.7 %
17mV
0.15 0.5 %
10 20 mV
1.05 1.20 V
1.10 1.25 V
1.15 1.30 V
0.5 10 mA
4.5 10 mA
0.08 0.2 %/W
60 75 dB
60 130 µA
0.2 5 µA
0.5 %
0.3 %
0.003 %
Copyright © 1999
Rev. 0.4 1/99
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Page 4
PRODUCT DATABOOK 1996/1997
LX8415-xx
0.5A LOW DROPOUT POSITIVE REGULATORS
RELIMINARY DATA SHEET
P
APPLICATION NOTES
The LX8415 series ICs are easy to use Low-Dropout (LDO) voltage
regulators. They have the standard self-protection features expected of a voltage regulator: short circuit protection and automatic
thermal shutdown if the device temperature rises above approximately 165°C.
Use of an output capacitor is REQUIRED with the LX8415 series.
Please see the table below for recommended minimum capacitor
values.
These regulators offer a more tightly controlled reference voltage
tolerance and superior reference stability when measured against
the older pin-compatible regulator types that they replace.
STABILITY
The output capacitor is part of the regulator’s frequency compensation system. Many types of capacitors are available, with different
capacitance value tolerances, capacitance temperature coefficients,
and equivalent series impedances. For all operating conditions,
connection of a 220µF aluminum electrolytic capacitor or a 47µF
solid tantalum capacitor between the output terminal and ground
will guarantee stable operation.
If a bypass capacitor is connected between the output voltage
adjust (ADJ) pin and ground, ripple rejection will be improved
(please see the section entitled “RIPPLE REJECTION”). When ADJ
pin bypassing is used, the required output capacitor value increases.
Output capacitor values of 220µF (aluminum) or 47µF (tantalum)
provide for all cases of bypassing the ADJ pin. If an ADJ pin bypass
capacitor is not used, smaller output capacitor values are adequate.
The table below shows recommended minimum capacitance values
for stable operation.
RECOMMENDED CAPACITOR VALUES
INPUT OUTPUT ADJ
10µF 15µF Tantalum, 100µF Aluminum None
10µF 47µF Tantalum, 220µF Aluminum 15µF
In order to ensure good transient response from the power supply
system under rapidly changing current load conditions, designers
generally use several output capacitors connected in parallel. Such
an arrangement serves to minimize the effects of the parasitic
resistance (ESR) and inductance (ESL) that are present in all
capacitors. Cost-effective solutions that sufficiently limit ESR and
ESL effects generally result in total capacitance values in the range
of hundreds to thousands of microfarads, which is more than
adequate to meet regulator output capacitor specifications. Output
capacitance values may be increased without limit.
The circuit shown in Figure 1 can be used to observe the transient
response characteristics of the regulator in a power system under
changing loads. The effects of different capacitor types and values
on transient response parameters, such as overshoot and undershoot, can be quickly compared in order to develop an optimum
solution.
Minumum Load
Power Supply
IN
LX8415-xx
ADJ
C
1
FIGURE 1 — DYNAMIC INPUT and OUTPUT TEST
OUT
Star Ground
C
2
(Larger resistor)
Full Load
(Smaller resistor)
R
DSON
10ms
RIPPLE REJECTION
Ripple rejection can be improved by connecting a capacitor
between the ADJ pin and ground. The value of the capacitor should
be chosen so that the impedance of the capacitor is equal in
magnitude to the resistance of R1 at the ripple frequency. The
capacitor value can be determined by using this equation:
C = 1 / (6.28 * F
* R1)
R
where: C ≡ the value of the capacitor in Farads;
select an equal or larger standard value.
F
≡ the ripple frequency in Hz
R
R1 ≡ the value of resistor R1 in ohms
At a ripple frequency of 120Hz, with R1 = 100Ω:
C = 1 / (6.28 * 120Hz
100Ω) = 13.3µF
*
The closest equal or larger standard value should be used, in this
case, 15µF.
When an ADJ pin bypass capacitor is used, output ripple
amplitude will be essentially independent of the output voltage. If
an ADJ pin bypass capacitor is not used, output ripple will be
proportional to the ratio of the output voltage to the reference
voltage:
M = V
OUT/VREF
where: M ≡ a multiplier for the ripple seen when the
ADJ pin is optimally bypassed.
= 1.25V.
V
REF
For example, if V
= 2.5V the output ripple will be:
OUT
M = 2.5V/1.25V= 2
Output ripple will be twice as bad as it would be if the ADJ pin
were to be bypassed to ground with a properly selected capacitor.
<< R
1 sec
L
4
Copyright © 1999
Rev. 0.4 1/99
Page 5
PRODUCT DATABOOK 1996/1997
LX8415-xx
OUT
IN
ADJ
V
IN
R1
R2
R
L
R
P
Parasitic
Line Resistance
Connect
R1 to Case
of Regulator
Connect
R2
to Load
0.5A LOW DROPOUT POSITIVE REGULATORS
P RELIMINARY DATA SHEET
APPLICATION NOTES
LX8415-xx
OUTPUT VOLTAGE
The LX8
415
ICs develop a 1.25V reference voltage between the output
LOAD REGULATION (continued)
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 I
through R1, it represents a small error and can usually be ignored.
is very small and constant when compared with the current
ADJ
LX8415-xx
ADJ
R2
R1
OUT
ADJ
R2
V
OUT
V
R1
REF
FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION
R2
is important to keep the connection between the regulator output
pin and the load as short as possible, and to use wide traces or
V
IN
IN
I
ADJ
50µA
V
= V
OUT
1 + + I
REF
heavy-gauge wire.
FIGURE 2 — BASIC ADJUSTABLE REGULATOR
The minimum specified output capacitance for the regulator
should be located near the reglator package. If several capacitors
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
are used in parallel to construct the power system output capacitance, 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 V
during transients.
IN (MIN)
connected to the load, the effective resistance between the regulator
V
= V
and the load would be:
R2+R1
= RP
R
where: R
Peff
*
R1
≡ Actual parasitic line resistance.
P
IN (MIN)
where: V
When the circuit is connected as shown in Figure 3, the parasitic
resistance appears as its actual value, rather than the higher R
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
Peff
.
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 junction 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.
+ V
OUT
IN (MIN)
V
OUT
V
DROPOUT (MAX)
DROPOUT (MAX)
≡ the lowest allowable instantaneous
voltage at the input pin.
≡ the designed output voltage for the
power supply system.
≡ the specified dropout voltage
for the installed regulator.
Copyright © 1999
Rev. 0.4 1/99
5
Page 6
LX8415-xx
T
A
THERMAL CONSIDERATIONS (continued)
Example
Given: V
Find: The size of a square area of 1oz. copper circuit-
Solution: The junction temperature is:
where: P
= 5.0V ±5%, V
IN
= 0.5A, TA = 55°C, TJ = 125°C
I
OUT
R
= 15°C/W, R
θJT
board trace-foil that will serve as a heatsink,
adequate to maintain the junction temperature of the
LX8415 in the ST (SOT-223) package within
specified limits.
= PD (R
T
J
D
R
θJT
R
θTS
+ R
θJT
≡ Dissipated power.
≡ Thermal resistance from the junction to the
mounting tab of the package.
≡ Thermal resistance through the interface
between the IC and the surface on which
it is mounted.
R
≡
Thermal resistance from the mounting surface
θSA
of the heatsink to ambient.
T
≡ Heat sink temperature.
S
J
T
R
q
JT
PRODUCT DATABOOK 1996/1997
0.5A LOW DROPOUT POSITIVE REGULATORS
RELIMINARY DATA SHEET
P
APPLICATION NOTES
First, find the maximum allowable thermal resistance of the
= 2.5V ±3%
OUT
= 5°C/W
θTS
+ R
θCS
C
R
q
CS
θSA
) + T
T
S
A
T
R
q
SA
heat sink:
P
= [[V
D
IN
PD= 1.4W
TJ - T
R
= - (R
θSA
P
A test was conducted to determine the thermal characteristics of
1 oz. copper circuit-board trace material. The following equation
describes the observed relationship between the area of a square
copper pad, and the thermal resistance from the tab of a SOT-223
package soldered at the center of the pad to ambient.
Area
= in
SINK
Substituting the value for R
square pad with area:
Area
= 0.43 in2 (0.66" x 0.66"), 280mm2 (17 x 17 mm)
SINK
will be required to maintain the LX8415 junction temperature
within specified limits.
(1 + Tol
*
A
D
3.1°C/W
R
- 22.3°C/W
θSA
)] - [V
VIN
+ R
θJT
calculated above, we find that a
θSA
) , R
θTS
* (1 - Tol
OUT
2
VOUT
= 29.6°C/W
θSA
)]] * I
OUT
6
Copyright © 1999
Rev. 0.4 1/99
Page 7
PRODUCT DATABOOK 1996/1997
LX8415-xx
OUT
IN
ADJ
V
OUT
**
V
IN
R1
121
Ω
R2
1k
C1*
10µF
* Needed if device is far from filter capacitors.
** V
OUT
= 1.25V 1 +
C2
100µF
R2
R1
(Note A)
0.5A LOW DROPOUT POSITIVE REGULATORS
P RELIMINARY DATA SHEET
TYPICAL APPLICATIONS
LX8415-xx
(Note A)
V
IN
10µF
LX8415-xx
IN
ADJ
* C1 improves ripple rejection.
should be ≈ R1 at ripple
X
C
frequency.
or 100µF Aluminum
OUT
R1
121
1%
R2
Ω
365
1%
V
IN
10µF Tantalum
5V
V
OUT
Ω
150µF
C1
10µF*
FIGURE 5 — 1.2V - 6V ADJUSTABLE REGULATORFIGURE 4 — IMPROVING RIPPLE REJECTION
LX8415-33
IN
OUT
GND
FIGURE 6 — FIXED 3.3V OUTPUT REGULATOR
3.3V
Min. 15µF Tantalum or
100µF Aluminum capacitor.
May be increased without
limit. ESR must be less
than 50m
Ω
.
Note A: V
= (Intended V
IN (MIN)
Copyright © 1999
Rev. 0.4 1/99
OUT
) + (V
DROPOUT (MAX)
)
PRELIMINARY DATA - Information contained in this document is pre-production data, and is proprietary to LinFinity. It may
not modified in any way without the express written consent of LinFinity. Product referred to herein is offered in sample form
only, and Linfinity reserves the right to change or discontinue this proposed product at any time.
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