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LIN D O C #: 8415
LX8415-xx
0 . 5 A L O W D ROPOUT P OSITIVE REGULATORS
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DESCRIPTION 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 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 10F 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.
K E Y F E AT U R E S
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 s s s s Battery Chargers 5V To 3.3V Linear Regulators Post Regulators For Switching Supplies Modems DVD Players
NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.
PRODUCT HIGHLIGHT
LOW COST 5V
TO
3.3V REGULATOR
AVAILABLE OPTIONS
PER
PA RT #
Output Voltage
2.5V 3.3V Adjustable
VIN 5V
LX8415-xx OUT IN ADJ 10F
R1 60.4 R2 100
VOUT 3.3V 22F
Part #
LX8415-25 LX8415-33 LX8415-00
PA C K A G E O R D E R I N F O TA (C) 0 to 125
ST Plastic SOT-223 3-pin
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.
Copyright (c) 1999 Rev. 0.4 1/99
LINFINITY MICROELECTRONICS INC.
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
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PRODUCT DATABOOK 1996/1997
LX8415-xx
0 . 5 A L O W D ROPOUT P OSITIVE R EGULATORS
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A B S O LUT E M AXIM UM R ATINGS
(Note 1)
PACKAGE PIN OUTS
TAB IS V OUT 3. IN 2. OUT 1. ADJ / GND
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) .......................................................................... 150C Storage Temperature Range ...................................................................... -65C to 150C Lead Temperature (Soldering, 10 seconds) ............................................................. 300C 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.
ST PACKAGE (Top View)
T H E R MAL DATA
ST PACKAGE: THERMAL RESISTANCE-JUNCTION TO TAB, JT THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA 15C/W *150C/W
Junction Temperature Calculation: TJ = TA + (PD x JA). The JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. * JAcan be improved with package soldered to 0.5IN2 copper area over backside ground plane or internal power plane. JAcan vary from 20C/W to > 40C/W depending on mounting technique. (See Application Notes Section: Thermal Considerations)
BLOCK D IA GR A M
VIN
Bias Circuit Thermal Limit Circuit Bandgap Circuit Control Circuit Output Circuit
VOUT
ADJ
Current Limit Circuit
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Copyright (c) 1999 Rev. 0.4 1/99
PRODUCT DATABOOK 1996/1997
LX8415-xx
0 . 5 A L O W D ROPOUT P OSITIVE REGULATORS
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R E C O M M E N D E D O P E R AT I N G C O N D I T I O N S Parameter
Input Voltage Operating Voltage LX8415-xx Operating Ambient Temperature Range Note 2. Range over which the device is functional.
(Note 2)
Symbol
Recommended Operating Conditions Min. Typ. Max.
7 125
Units
0
V C
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified: 0C TJ 125C, IMAX = 0.5A for the LX8415-xx.)
Parameter
Reference Voltage Output Voltage LX8415-00 LX8415-25 LX8415-33 Line Regulation (Note 3) Load Regulation (Note 3) Dropout Voltage (Note 4) LX8415-00 LX8415-25 / 33 LX8415-00 LX8415-25 / 33 LX8415-xx
Symbol
VREF
Test Conditions
IOUT = 10mA, (VIN - VOUT) = 2V, TJ = 25C 10mA IOUT IMAX, 1.5V (VIN - VOUT) 6V IOUT = 10mA, VIN = 5V, TJ = 25C 0mA IOUT IMAX, 4.75V V IN 6V IOUT = 10mA, VIN = 5V, TJ = 25C 0mA IOUT IMAX, 4.75V V IN 6V I OUT = 10mA, 1.5V VIN - V OUT 6V I OUT = 0mA, 4.75V V IN 6V (V IN - VOUT) = 3V, 10mA IOUT IMAX VIN = 4.75V, 0mA IOUT IMAX IOUT = 100mA IOUT = 300mA IOUT = IMAX (V IN - VOUT) 1.3V, T J = 25C VIN 6V, (LX8415-00) VIN 6V TA = 25C, 30ms Pulse fRIPPLE = 120Hz, (VIN - VOUT ) = 3V, VRIPPLE = 1Vp - p
Min.
1.238 1.225 2.475 2.450 3.267 3.235
LX8415-xx Typ. Max.
1.250 1.250 2.500 2.500 3.300 3.300 0.05 1 0.15 10 1.05 1.10 1.15 950 0.5 4.5 0.08 75 60 0.2 0.5 0.3 0.003 1.262 1.275 2.525 2.550 3.333 3.365 0.7 7 0.5 20 1.20 1.25 1.30 10 10 0.2 130 5
Units
V V V V V V % mV % mV V V V mA mA mA %/W dB A A % % %
Current Limit LX8415-xx I OUT (MAX) Minimum Load Current (Note 5) Quiescent Current LX8415-25 / 33 Thermal Regulation Ripple Rejection Adjust Pin Current LX8415(A)-00 Adjust Pin Current Change LX8415(A)-00 10mA IOUT IMAX, 1.5V (VIN - VOUT) 6V Temperature Stability Long Term Stability TA = 125C, 1000Hrs RMS Output Noise (% of V OUT), 10Hz f 10kHz
500
60
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.
Copyright (c) 1999 Rev. 0.4 1/99
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PRODUCT DATABOOK 1996/1997
LX8415-xx
0 . 5 A L O W D ROPOUT P OSITIVE R EGULATORS
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A P P L I C AT I O N N O T E S 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 165C. 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 220F aluminum electrolytic capacitor or a 47F 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 220F (aluminum) or 47F (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
10F 10F
Power Supply IN
LX8415-xx
ADJ
OUT
Minumum Load (Larger resistor) Full Load (Smaller resistor)
C1
C2
RDSON << RL
1 sec
Star Ground
10ms
FIGURE 1 -- DYNAMIC INPUT and OUTPUT TEST
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 * FR * R1) where: C the value of the capacitor in Farads; select an equal or larger standard value. F R the ripple frequency in Hz R1 the value of resistor R1 in ohms
At a ripple frequency of 120Hz, with R1 = 100: C = 1 / (6.28 * 120Hz * 100) = 13.3F The closest equal or larger standard value should be used, in this case, 15F. 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 = VOUT/VREF where: M VREF a multiplier for the ripple seen when the ADJ pin is optimally bypassed. = 1.25V.
OUTPUT
15F Tantalum, 100F Aluminum 47F Tantalum, 220F Aluminum
ADJ
None 15F
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.
For example, if VOUT = 2.5V the output ripple will be: 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.
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Copyright (c) 1999 Rev. 0.4 1/99
PRODUCT DATABOOK 1996/1997
LX8415-xx
0 . 5 A L O W D ROPOUT P OSITIVE REGULATORS
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A P P L I C AT I O N N O T E S 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 IADJ is very small and constant when compared with the current through R1, it represents a small error and can usually be ignored.
LX8415-xx OUT IN ADJ IADJ 50A VOUT = VREF 1 + R2 + IADJ R2 R1 R2
LOAD REGULATION (continued)
LX8415-xx OUT ADJ RP Parasitic Line Resistance
Connect R1 to Case of Regulator
VIN
IN
R1 R2
RL Connect R2 to Load
VIN
VOUT VREF R1
FIGURE 3 -- CONNECTIONS FOR BEST LOAD REGULATION
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: R2+R1 RPeff = RP * 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
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 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 VIN (MIN) during transients. VIN (MIN) = VOUT + VDROPOUT (MAX) where: VIN (MIN) VOUT VDROPOUT (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.
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.
Copyright (c) 1999 Rev. 0.4 1/99
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PRODUCT DATABOOK 1996/1997
LX8415-xx
0 . 5 A L O W D ROPOUT P OSITIVE R EGULATORS
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A P P L I C AT I O N N O T E S THERMAL CONSIDERATIONS (continued) Example Given: VIN = 5.0V 5%, VOUT = 2.5V 3% IOUT = 0.5A, TA = 55C, TJ = 125C RJT = 15C/W, RTS = 5C/W Find: The size of a square area of 1oz. copper circuitboard 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. Solution: The junction temperature is: TJ = PD (RJT + RCS + R SA) + TA where: PD Dissipated power. RJT Thermal resistance from the junction to the mounting tab of the package. RTS Thermal resistance through the interface between the IC and the surface on which it is mounted. RSA Thermal resistance from the mounting surface of the heatsink to ambient. TS Heat sink temperature. First, find the maximum allowable thermal resistance of the heat sink: PD PD = [[VIN * (1 + TolVIN )] - [VOUT * (1 - TolVOUT)]] * IOUT = 1.4W TJ - TA - (RJT + R TS) , PD RSA = 29.6C/W
RSA =
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. AreaSINK = 3.1C/W in 2 R SA - 22.3C/W
Substituting the value for RSA calculated above, we find that a square pad with area: AreaSINK = 0.43 in2 (0.66" x 0.66"), 280mm 2 (17 x 17 mm) will be required to maintain the LX8415 junction temperature within specified limits.
TJ Rq JT
TC Rq CS
TS Rq SA
TA
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Copyright (c) 1999 Rev. 0.4 1/99
PRODUCT DATABOOK 1996/1997
LX8415-xx
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T Y P I C A L A P P L I C AT I O N S
(Note A)
VIN 10F
LX8415-xx OUT IN ADJ
5V R1 121 1% C1 10F*
VOUT
VIN
(Note A)
IN C1* 10F
LX8415-xx OUT ADJ
VOUT** R1 121 C2 100F
150F
* C1 improves ripple rejection. XC should be R1 at ripple frequency.
R2 365 1%
R2 1k
* Needed if device is far from filter capacitors. ** VOUT = 1.25V 1 + R2 R1
FIGURE 4 -- IMPROVING RIPPLE REJECTION
FIGURE 5 -- 1.2V - 6V ADJUSTABLE REGULATOR
LX8415-33 VIN 10F Tantalum or 100F Aluminum IN GND OUT 3.3V Min. 15F Tantalum or 100F Aluminum capacitor. May be increased without limit. ESR must be less than 50m.
FIGURE 6 -- FIXED 3.3V OUTPUT REGULATOR
Note A: VIN (MIN) = (Intended VOUT ) + (VDROPOUT (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.
Copyright (c) 1999 Rev. 0.4 1/99
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