p reliminary d ata s heet t he i nfinite p ower of i nnovation m icrosemi inc . 11861 w estern a venue , g arden g rove , ca. 92841, 714-898-8121, f ax : 714-893-2570 1 copyright ? 1999 rev. 0.5,2005-06-16 lx8415-xx 0.5a l ow d ropout p ositive r egulators 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 dropou t 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. on chip trimming of the internal voltage reference allows specification of the init ial 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 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 low profile plastic sot-223 packag e for applications where space is at a premium. important: for the most current data, consult microsemi ?s website: http://www.microsemi.com product highlight low cost 5v to 3.3v regulator lx8415-xx v in 5v 10f in adj out v out 3.3v 22f r 2 100 ? r 1 60.4 ? key features ? 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 key features ? battery chargers ? 5v to 3.3v linear regulators ? post regulators for switching supplies ? modems ? dvd players available options per part # part # output voltage lx8415-25 2.5v lx8415-33 3.3v lx8415-00 adjustable package order info st plastic sot-223 3-pin t a ( c) rohs compliant / pb-free transition dc: 0522 0 to 125 lx8415-xxcst note: available in tape & reel. append the letter ?tr? to the part number. (i.e. lx8415-25cst-tr)
0.5a l ow d ropout p ositive r egulators lx8415-xx product databook 1996/1997 copyright ? 1999 rev. 0.5 2 p reliminary d ata s heet absolute maximum ratings (note 1) power dissipation .................................................................................. internally limited input voltage lx8415-00 (adjustable) / 8415-33 (3.3v) .................................................................. 7v surge voltage ................................................................................................................. 7 v 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. package pin outs 3. in 2. out 1. adj / gnd st package (top view) thermal data st package: thermal resistance-junction to tab, q q q q q jt 15c/w thermal resistance-junction to ambient, q q q q q ja *150c/w junction temperature calculation: t j = t a + (p d x q ja ). the q ja numbers are guidelines for the thermal performance of the device/pc-board system. all of the above assume no ambient airflow. * q ja can be improved with package soldered to 0.5in 2 copper area over backside ground plane or internal power plane. q ja can vary from 20oc/w to > 40oc/w depending on mounting technique. (see application notes section: thermal considerations) tab is v out block diagram thermal limit circuit control circuit bandgap circuit output circuit bias circuit v ou t v in current limit circuit a dj rohs peak package solder reflow temp. (40 seconds max. exposure)............................. 260c (+0, -5) rohs / pb-free 100% matte tin lead finish
0.5a l ow d ropout p ositive r egulators lx8415-xx product databook 1996/1997 3 copyright ? 1999 rev. 0.5 p reliminary d ata s heet input voltage operating voltage lx8415-xx operating ambient temperature range recommended operating conditions (note 2) parameter symbol units recommended operating conditions min. typ. max. 7v 0 125 c note 2. range over which the device is functional. 1.238 1.250 1.262 v 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 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 500 950 ma 0.5 10 ma 4.5 10 ma 0.08 0.2 %/w 60 75 db 60 130 a 0.2 5 a 0.5 % 0.3 % 0.003 % electrical characteristics (unless otherwise specified: 0c t j 125c, i max = 0.5a for the lx8415-xx.) parameter symbol test conditions units lx8415-xx min. typ. max. reference voltage lx8415-00 v ref i out = 10ma, (v in - v out ) = 2v, t j = 25c 10ma i out i max , 1.5v (v in - v out ) 6v output voltage lx8415-25 i out = 10ma, v in = 5v, t j = 25c 0ma i out i max , 4.75v v in 6v lx8415-33 i out = 10ma, v in = 5v, t j = 25c 0ma i out i max , 4.75v v in 6v line regulation lx8415-00 i out = 10ma, 1.5v v in - v out 6v (note 3) lx8415-25 / 33 i out = 0ma, 4.75v v in 6v load regulation lx8415-00 (v in - v out ) = 3v, 10ma i out i max (note 3) lx8415-25 / 33 v in = 4.75v, 0ma i out i max dropout voltage lx8415-xx i out = 100ma (note 4) i out = 300ma i out = i max current limit lx8415-xx i out (max) (v in - v out ) 3 1.3v, t j = 25c minimum load current (note 5) v in 6v, (lx8415-00) quiescent current lx8415-25 / 33 v in 6v thermal regulation t a = 25c, 30ms pulse ripple rejection f ripple = 120hz, (v in - v out ) = 3v, v ripple = 1vp - p adjust pin current lx8415(a)-00 adjust pin current change lx8415(a)-00 10ma i out i max , 1.5v (v in - v out ) 6v temperature stability long term stability t a = 125c, 1000hrs rms output noise (% of v out ), 10hz f 10khz notes: 3. see thermal regulation specification for changes in output voltage due to heating effects. load regulation and line re gulation 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 inp ut/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.
0.5a l ow d ropout p ositive r egulators lx8415-xx product databook 1996/1997 copyright ? 1999 rev. 0.5 4 p reliminary d ata s heet application notes the lx8415 series ics are easy to use low-dropout (ldo) voltage regulators. they have the standard self-protection features ex- pected of a voltage regulator: short circuit protection and automatic thermal shutdown if the device temperature rises above approxi- mately 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 regulators frequency compen- sation 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. input output adj 10f 15f tantalum, 100f aluminum none 10f 47f tantalum, 220f aluminum 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 under- shoot, can be quickly compared in order to develop an optimum solution. recommended capacitor values figure 1 dynamic input and output test lx8415-xx power supply out in adj star ground 1 sec 10ms r dson << r l full load (smaller resistor) minumum load (larger resistor) c 1 c 2 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 r * r1) where: c o the value of the capacitor in farads; select an equal or larger standard value. f r o the ripple frequency in hz r1 o the value of resistor r1 in ohms at a ripple frequency of 120hz, with r1 = 100 w : c = 1 / (6.28 * 120hz * 100 w ) = 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 = v out /v ref where: m o a multiplier for the ripple seen when the adj pin is optimally bypassed. v ref = 1.25v. for example, if v out = 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.
0.5a l ow d ropout p ositive r egulators lx8415-xx product databook 1996/1997 5 copyright ? 1999 rev. 0.5 p reliminary d ata s heet application notes figure 2 basic adjustable regulator r2+r1 r1 ?? ? lx8415-xx out in adj v out v in r1 r2 v ref i adj 50a v out = v ref 1 + + i adj r2 r2 r1 output voltage the lx8 415 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 i adj 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 v in r1 r2 r l r p parasitic line resistance connect r1 to case of regulator connect r2 to load figure 3 connections for best load regulation load regulation because the lx8 415 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: r peff = r p * where: r p o 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 r peff . 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) 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 v in (min) during transients. v in (min) = v out + v dropout (max) where: v in (min) o the lowest allowable instantaneous voltage at the input pin. v out o the designed output voltage for the power supply system. v dropout (max) o the specified dropout voltage for the installed regulator. thermal considerations the lx8 415 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.
0.5a l ow d ropout p ositive r egulators lx8415-xx product databook 1996/1997 copyright ? 1999 rev. 0.5 6 p reliminary d ata s heet application notes thermal considerations (continued) example given: v in = 5.0v 5%, v out = 2.5v 3% i out = 0.5a, t a = 55c, t j = 125c r q jt = 15c/w, r q ts = 5c/w find: the size of a square area of 1oz. copper circuit- 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. solution: the junction temperature is: t j = p d (r q jt + r q cs + r q sa ) + t a where: p d o dissipated power. r q jt o thermal resistance from the junction to the mounting tab of the package. r q ts o thermal resistance through the interface between the ic and the surface on which it is mounted. r q sa o thermal resistance from the mounting surface of the heatsink to ambient. t s o heat sink temperature. t j t c t s t a r q jt r q cs r q sa t j - t a p d 3.1c/w r q sa - 22.3c/w first, find the maximum allowable thermal resistance of the heat sink: p d = [ [v in * (1 + tol vin )] - [v out * (1 - tol vout )] ] * i out p d = 1.4w r q sa = - (r q jt + r q ts ) , r q sa = 29.6c/w 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 sink = in 2 substituting the value for r q sa calculated above, we find that a square pad with area: area sink = 0.43 in 2 (0.66" x 0.66"), 280mm 2 (17 x 17 mm) will be required to maintain the lx8415 junction temperature within specified limits.
0.5a l ow d ropout p ositive r egulators lx8415-xx product databook 1996/1997 7 copyright ? 1999 rev. 0.5 p reliminary d ata s heet typical applications lx8415-xx out in adj 150f v in r2 365 w 1% 10f r1 121 w 1% c1 10f* * c1 improves ripple rejection. x c should be ? r1 at ripple frequency. v out 5v (note a) figure 5 1.2v - 6v adjustable regulator figure 4 improving ripple rejection lx8415-xx out in adj v out ** v in r1 121 w r2 1k c1* 10f * needed if device is far from filter capacitors. ** v out = 1.25v 1 + c2 100f r2 r1 (note a) figure 6 fixed 3.3v output regulator note a: v in (min) = (intended v out ) + (v dropout (max) ) 3.3v v in 10f tantalum or 100f aluminum min. 15f tantalum or 100f aluminum capacitor. may be increased without limit. esr must be less than 50m w . lx8415-33 out in gnd 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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