description key fea tures n n n n n three-terminal adjustable or fixed output voltage n n n n n guaranteed 1% voltage reference accuracy over line, load and temperature (lx8385b) n n n n n guaranteed < 1.5v headroom at 3a (lx8385) n n n n n guaranteed < 1.3v headroom at 3a (lx8385a/8385b) n n n n n output current of 3a minimum p 0.015% line regulation p 0.1% load regulation the lx8385/8385a/8385b series ics are positive regulators designed to provide 3a output current. each regulator yields higher efficiency than currently available devices with all internal circuitry designed to operate down to a 1v input-to-output- differential. in these products, the drop- out voltage is fully specified as a function of load current. the lx8385's dropout is guaranteed at a maximum of 1.5v at maxi- mum output current, decreasing at lower load currents. the lx8385a/85b have a maximum dropout voltage of 1.3v. the lx8385b offers a tighter voltage reference tolerance: 1.0% over line, load and temperature, with 0.8% initial accu- racy. the lx8385/85a have 1.0% initial accuracy, with 2% over line, load and tem- perature. the lx8385/85a/85b series devices are pin-compatible with earlier 3-terminal regulators, such as 117 series products. while a 10f output capacitor is required on both input and output of these new devices, this is generally included in most regulator designs. the quiescent current of the lx8385/ 85a/85b series products flows into the load, increasing efficiency. this feature contrasts with pnp regulator designs, where up to 10% of the output current is wasted as quiescent current. the lx8385-xxi is rated for -25c to +125c applications, and the lx8385-xxc /8385b-xxc is rated for 0c to +125c applications. product highlight 3.3v, 3 a r egulator applications n high efficiency linear regulators n post regulators for switching power supplies n battery chargers n constant current regulators n graphics & standard supplies n processor i/o supply n low voltage memory & chipset supplies 3a l ow d ropout p ositive r egulators p roduction d ata s heet t he i nfinite p ower of i nnova tion lx8385-xx/8385a-xx/8385b-xx lin d oc #: 8385 lx8385 200 w 1% 1% 3.3v at 3a 5v out in adj 1500f, 6.3v 6mv1500gx 2x 1500f, 6.3v 6mv1500gx from sanyo 121 w note: all surface-mount packages are available in tape & reel. append the letter "t" to part number (i.e. lx8385-00cddt). "xx" refers to output voltage, please see table above. * consult factory for availability of to-3 metal can. lx8385/85a/85b-00 adjustable lx8385/85a/85b-33 3.3v lx8385/85a/85b-05 5.0v part # output voltage a vailable o ptions per p art # other voltage options may be available please contact factory for details. package order information* t a (c) p 1.5v lx8385-xxcp lx8385-xxcdd lx8385-xxcdl 0 to 125 1.3v lx8385a-xxcp lx8385a-xxcdd lx8385a-xxcdl 1.3v lx8385b-xxcp lx8385b-xxcdd lx8385b-xxcdl -25 to 125 1.5v lx8385-xxip lx8385-xxidd dropout voltage plastic to-220 3-pin plastic to-263 3-pin dd copyright ? 1999 rev. 2.0 3/99 1 11861 w estern a venue , g arden g rove , ca. 92841, 714-898-8121, f ax : 714-893-2570 l in f inity m icroelectronics i nc . note: for current data & package dimensions, visit our web site: http://www.linfinity.com. plastic to-263 (non-jeded) 3-pin dl
3a l ow d ropout p ositive r egulators lx8385-xx/8385a-xx/8385b-xx product databook 1996/1997 copyright ? 1999 rev. 2.0 3/99 2 p roduction d ata s heet absolute maximum ratings (note 1) power dissipation .................................................................................. internally limited input voltage ................................................................................................................ 10 v input to output voltage differential ........................................................................... 10v operating junction temperature plastic (p, dd & dl packages) ............................................................................. 150c storage temperature range ...................................................................... -65c to 150c lead temperature (soldering, 10 seconds) ............................................................. 300c package pin outs thermal limit circuit control circuit bandgap circuit output circuit bias circuit v out v in soa protection circuit current limit circuit adj or gnd* block diagram p package: thermal resistance-junction to tab, jt 3.0c/w thermal resistance-junction to ambient, ja 60c/w dd & dl packages: thermal resistance-junction to tab, jt 3.0c/w thermal resistance-junction to ambient, ja *60c/w junction temperature calculation: t j = t a + (p d 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. * ja can be improved with package soldered to 0.5in 2 copper area over backside ground plane or internal power plane. ja can vary from 20oc/w to > 40oc/w depending on mounting technique. thermal data 3 2 1 p package (top view) * pin 1 is gnd for fixed voltage versions. 3 2 1 dd & dl packages (top view) * pin 1 is gnd for fixed voltage versions. 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. tab is v out tab is v out * this pin gnd for fixed voltage versions. v in v out adj / gnd* v in v out adj / gnd*
3a l ow d ropout p ositive r egulators lx8385-xx/8385a-xx/8385b-xx product databook 1996/1997 3 copyright ? 1999 rev. 2.0 3/99 p roduction d ata s heet electrical characteristics (unless otherwise specified, these specifications apply over the operating ambient temperatures for the lx8385-xxc/85a/85b-xxc with 0c t a 125c and the lx8385-xxi with -25c t a 125c; v in - v out = 3v; i out = 3a. low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.) parameter symbol test conditions units lx8385/85a/85b-00 min. typ. max. reference voltage lx8385-00 v ref i out = 10ma, t a = 25c (note 4) 10ma i out i out (max) , 1.5v (v in - v out ), v in 10v, p p max lx8385a/85b-00 i out = 10ma, t a = 25c 10ma i out i out (max) , 1.5v (v in - v out ), v in 10v, p p max line regulation (note 2) ? v ref (v in ) 1.5v (v in - v out ) 7v, i out = 10ma load regulation (note 2) ? v ref (i out ) v in - v out = 3v, 10ma i out 3a thermal regulation ? v out (pwr) t a = 25c, 20ms pulse ripple rejection (note 3) v out = 5v, f =120hz, c out = 100f tantalum, v in = 6.5v c adj = 10f, i out = 3a adjust pin current i adj adjust pin current change (note 4) ? i adj 10ma i out i out (max) , 1.5v (v in - v out ), v in 10v dropout voltage lx8385-00 ? v ? v ref = 1%, i out = 3a lx8385a/85b-00 ? v ref = 1%, i out = 3a minimum load current i out (min) v in 10v maximum output current i out (max) (v in - v out ) 7v, v in 10v temperature stability (note 3) ? v out (t) long term stability (note 3) ? v out (t) t a = 125c, 1000 hours rms output noise (% of v out ) (note 3) v out (rms) t a = 25c, 10hz f 10khz 1.238 1.250 1.262 v 1.225 1.250 1.270 v 1.240 1.250 1.260 v 1.238 1.250 1.262 v 0.015 0.2 % 0.2 0.5 % 0.01 0.04 %/w 65 83 db 55 100 a 0.2 5 a 1.2 1.5 v 1.1 1.3 v 210ma 3 3.5 a 0.25 % 0.3 1 % 0.003 % parameter symbol test conditions units lx8385/85a/85b-33 min. typ. max. output voltage lx8385-33 v out v in = 5v, i out = 0ma, t a = 25c (note 4) 4.75v v in 10v, 0ma i out 3a, p p max lx8385a/85b-33 v in = 5v, i out = 0ma, t a = 25c 4.75v v in 10v, 0ma i out 3a, p p max line regulation (note 2) ? v out 4.75v v in 7v (v in ) 4.75v v in 10v load regulation (note 2) ? v out (i out ) v in = 5v, 0ma i out i out (max) thermal regulation ? v out (pwr) t a = 25c, 20ms pulse ripple rejection (note 3) c out = 100f (tantalum), i out = 3a quiescent current i q 0ma i out i out (max) , 4.75v v in 10v dropout voltage lx8385-33 ? v ? v out = 1%, i out i out (max) lx8385a/85b-33 ? v out = 1%, i out i out (max) maximum output current i out (max) v in 7v temperature stability (note 3) ? v out (t) long term stability (note 3) ? v out (t) t a = 125c, 1000 hours rms output noise (% of v out ) (note 3) v out (rms) t a = 25c, 10hz f 10khz 3.267 3.3 3.333 v 3.235 3.3 3.365 v 3.274 3.3 3.326 v 3.267 3.3 3.333 v 16mv 210mv 515mv 0.01 0.02 % / w 60 83 db 410ma 1.2 1.5 v 1.1 1.3 v 3 3.5 a 0.25 % 0.3 1 % 0.003 % note 2. regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. changes in output v oltage due to heating effects are covered under the specification for thermal regulation. note 3. these parameters, although guaranteed, are not tested in production. note 4. see maximum output current section above. lx8385-00/85a/85b-00 (adjustable) lx8385-33/85a-33/85b-33 (3.3v fixed)
3a l ow d ropout p ositive r egulators lx8385-xx/8385a-xx/8385b-xx product databook 1996/1997 copyright ? 1999 rev. 2.0 3/99 4 p roduction d ata s heet electrical characteristics parameter symbol test conditions units lx8385/85a/85b-05 min. typ. max. output voltage lx8385-05 v out v in = 7v, i out = 0ma, t a = 25c (note 4) 7v v in 10v, 0ma i out 3a, p p max lx8385a/85b-05 v in = 7v, i out = 0ma, t a = 25c 7v v in 10v, 0ma i out 3a, p p max line regulation (note 2) ? v out (v in ) 4.75v v in 10v load regulation (note 2) ? v out (i out ) v in = 7v, 0ma i out i out (max) thermal regulation ? v out (pwr) t a = 25c, 20ms pulse ripple rejection (note 3) c out = 100f (tantalum), i out = 3a quiescent current i q 0ma i out i out (max) , 7v v in 10v dropout voltage lx8385- 05 ? v ? v out = 1%, i out i out (max) lx8385a/85b-05 ? v out = 1%, i out i out (max) maximum output current i out (max) v in 10v temperature stability (note 3) ? v out (t) long term stability (note 3) ? v out (t) t a = 125c, 1000 hours rms output noise (% of v out ) (note 3) v out (rms) t a = 25c, 10hz f 10khz 4.950 5.00 5.050 v 4.900 5.00 5.100 v 4.960 5.00 5.040 v 4.950 5.00 5.050 v 210mv 525mv 0.01 0.02 % / w 60 83 db 410ma 1.2 1.5 v 1.1 1.3 v 3 3.5 a 0.25 % 0.3 1 % 0.003 % note 2. regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. changes in output v oltage due to heating effects are covered under the specification for thermal regulation. note 3. these parameters, although guaranteed, are not tested in production. note 4. see maximum output current section above. lx8385-05/85a-05/85b-05 (5.0v fixed)
3a l ow d ropout p ositive r egulators lx8385-xx/8385a-xx/8385b-xx product databook 1996/1997 5 copyright ? 1999 rev. 2.0 3/99 p roduction d ata s heet application notes the lx8385/85a/85b series ics are easy to use low-dropout (ldo) voltage regulators. they have all of the standard self-protection features expected of voltage regulators: short circuit protection, safe operating area protection and automatic thermal shutdown if the device temperature rises above approximately 165c. use of an output capacitor is required with the lx8385/85a/ 85b 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. in order to ensure good transient response from the power supply input output adj 10f 15f tantalum, 100f aluminum none 10f 47f tantalum, 220f aluminum 15f 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 lx8385 /85a/85b power supply out in adj star ground 1 sec 10ms r dson << r l full load (smaller resistor) minumum load (larger resistor) overload recovery like almost all ic power regulators, the lx8385/85a/85b regulators are equipped with safe operating area (soa) protection. the soa circuit limits the regulator's maximum output current to progres- sively lower values as the input-to-output voltage difference increases. by limiting the maximum output current, the soa circuit keeps the amount of power that is dissipated in the regulator itself within safe limits for all values of input-to-output voltage within the operating range of the regulator. the lx8385/85a/85b soa protection system is designed to be able to supply some output current for all values of input-to-output voltage, up to the device breakdown voltage. under some conditions, a correctly operating soa circuit may prevent a power supply system from returning to regulated operation after removal of an intermittent short circuit at the output of the regulator. this is a normal mode of operation which can be seen in most similar products, including older devices such as 7800 series regulators. it is most likely to occur when the power system input voltage is relatively high and the load impedance is relatively low. when the power system is started cold, both the input and output voltages are very close to zero. the output voltage closely follows the rising input voltage, and the input-to-output voltage difference is small. the soa circuit therefore permits the regulator to supply large amounts of current as needed to develop the designed voltage level at the regulator output. now consider the case where the regulator is supplying regulated voltage to a resistive load under steady state conditions. a moderate input-to-output voltage appears across the regulator but the voltage difference is small enough that the soa circuitry allows sufficient current to flow through the regulator to develop the designed output voltage across the load resistance. if the output resistor is short-circuited to ground, the input-to-output voltage difference across the regulator suddenly becomes larger by the amount of voltage that had appeared across the load resistor. the soa circuit reads the increased input-to- output voltage, and cuts back the amount of current that it will permit the regulator to supply to its output terminal. when the short circuit across the output resistor is removed, all the regulator output current will again flow through the output resistor. the maximum current that the regulator can supply to the resistor will be limited by the soa circuit, based on the large input-to-output voltage across the regulator at the time the short circuit is removed from the output.
3a l ow d ropout p ositive r egulators lx8385-xx/8385a-xx/8385b-xx product databook 1996/1997 copyright ? 1999 rev. 2.0 3/99 6 p roduction d ata s heet application notes figure 2 basic adjustable regulator r2+r1 r1 ?? ?? lx8385/85a/85b out in adj v out v in r1 r2 v ref i adj 50a v out = v ref 1 + + i adj r2 r2 r1 overload recovery (continued) if this limited current is not sufficient to develop the designed voltage across the output resistor, the voltage will stabilize at some lower value, and will never reach the designed value. under these circumstances, it may be necessary to cycle the input voltage down to zero in order to make the regulator output voltage return to regulation. 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 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 = v out /v ref where: m 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. output voltage the lx8385 /85a/85b 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. load regulation because the lx8385 /85a/85b 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 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 . lx8385/85a/85b 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
3a l ow d ropout p ositive r egulators lx8385-xx/8385a-xx/8385b-xx product databook 1996/1997 7 copyright ? 1999 rev. 2.0 3/99 p roduction d ata s heet application notes example given: v in = 5v v out = 2.5v, i out = 1.5a ambient temp., t a = 50c r jt = 2.7c/w for to-220 find: proper heat sink to keep ic's junction temperature below 125c.** solution: the junction temperature is: t j = p d (r jt + r cs + r sa ) + t a where: p d dissipated power. r jt thermal resistance from the junction to the mounting tab of the package. r cs thermal resistance through the interface between the ic and the surface on which it is mounted. (1.0c/w at 6 in-lbs mounting screw torque.) r sa thermal resistance from the mounting surface to ambient (thermal resistance of the heat sink). t s heat sink temperature. first, find the maximum allowable thermal resistance of the heat sink: r sa = - (r jt + r cs ) p d =(v in(max) - v out ) i out = (5.0v-2.5v) * 1.5a = 3.75w r sa = - (2.7c/w + 1.0c/w) = 16.3c/w next, select a suitable heat sink. the selected heat sink must have r sa 16.3c/w. thermalloy heatsink 6230b has r sa = 12.0c/w. finally, verify that junction temperature remains within speci- fication using the selected heat sink: t j = 3.75w (2.7c/w + 1.0c/w + 12.0c/w) + 50c = 109c t j t c t s t a r q jt r q cs r q sa t j - t a p d 125c - 50c 3.75w ** although the device can operate up to 150c junction, it is recom- mended for long term reliability to keep the junction temperature below 125c whenever possible. load regulation (continued) even when the circuit is optimally configured, parasitic resistance can be a significant source of error. a 20 mil wide pc trace built from 1 oz. copper-clad circuit board material has a parasitic resistance of about 25 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 1.5 amps of current, a 75 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 2.43 volts, which is a 3% 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 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) the lowest allowable instantaneous voltage at the input pin. v out the designed output voltage for the power supply system. v dropout (max) the specified dropout voltage for the installed regulator. thermal considerations the lx8385 /85a/85b 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. junction-to-case thermal resistance is specified from the ic junction to the back surface of the case directly opposite the die. this is the lowest resistance path for heat flow. proper mounting is required to ensure the best possible thermal flow from this area of the package to the heat sink. thermal compound at the case-to- heat-sink interface is strongly recommended. if the case of the device must be electrically isolated, a thermally conductive spacer can be used, as long as its added contribution to thermal resistance is considered. note that the case of all devices in this series is electrically connected to the output.
3a l ow d ropout p ositive r egulators lx8385-xx/8385a-xx/8385b-xx product databook 1996/1997 copyright ? 1999 rev. 2.0 3/99 8 p roduction d ata s heet typical applications lx8385/85a/85b 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 - 8v adjustable regulator figure 4 improving ripple rejection lx8385/85a/85b 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 5v regulator with shutdown (note a) lx8385/85a/85b out in adj 5v v in 121 w 1% 10f 100f 365 w 1% 1k 1k 2n3904 ttl o utput note a: v in (min) = (intended v out ) + (v dropout (max) ) figure 7 fixed 3.3v output regulator lx8385/85a/85b-33 out in gnd 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 . production data - information contained in this document is proprietary to linfinity, and is current as of publication date. t his document may not be modified in any way without the express written consent of linfinity. product processing does not necessarily inclu de testing of all parameters. linfinity reserves the right to change the configuration and performance of the product and to discontinue pro duct at any time.
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