? semiconductor components industries, llc, 2002 may, 2002 rev. 5 1 publication order number: cs52081/d cs5208-1 8.0 a ldo 3-pin adjustable linear regulator the cs52081 linear regulator provides 8.0 a at adjustable voltages from 1.25 v to 4.5 v. this adjustable device requires two external resistors to set the output voltage and provide the minimum load current for proper regulation. this regulator is intended for use as a post regulator and microprocessor supply. the fast loop response and low dropout voltage make this regulator ideal for applications where low voltage operation and good transient response are important. the circuit is designed to operate with dropout voltages as low as 1.0 v at 8.0 a. the regulator is protected against overload conditions with overcurrent and thermal shutdown protection circuitry. the regulator is available in a to220 package. features ? 1.25 v to 4.5 v v out at 8.0 a ? dropout voltage < 1.0 v @ 8.0 a ? 1.5% trimmed reference ? fast transient response ? thermal shutdown ? current limit ? short circuit protection figure 1. applications diagram cs52081 v in v out adj 100 m f 5.0 v 0.1 m f load 124 200 300 m f 3.3 v @ 8.0 a device package shipping ordering information cs52081gt3 to220* 50 units/rail *to220 is 3pin, straight leaded. to220 three lead t suffix case 221a pin connections and marking diagrams cs52081 awlyww 1 a = assembly location wl, l = wafer lot yy, y = year ww, w = work week tab = v out pin 1. adjust 2. v out 3. v in 1 2 3 http://onsemi.com
cs52081 http://onsemi.com 2 maximum ratings* parameter value unit input voltage 6.0 v operating junction temperature range 0 t j 150 c storage temperature range 60 to +150 c lead temperature soldering: wave solder (through hole styles only) note 1 260 peak c esd damage threshold 2.0 kv 1. 10 second maximum. *the maximum package power dissipation must be observed. electrical characteristics ( 0 c t a 70 c, 0 c t j 150 c, v adj = 0 v, unless otherwise specified.) characteristic test conditions min typ max unit adjustable output voltage reference voltage v in = 2.75 v to 5.5 v, i out = 10 ma to 8.0 a 1.234 (1.5%) 1.253 1.271 (+1.5%) v line regulation v in = 2.75 v to 5.5 v, i out = 10 ma 0.02 0.20 % load regulation v in = 2.75 v, i out = 10 ma to 8.0 a 0.04 0.50 % minimum load current (note 2) v in = 5.0 v, d v out = +1.5% 5.0 10 ma adjust pin current v in = 2.75 v, i out = 10 ma 70 120 m a current limit v in = 2.75 v, d v out = 1.5% 8.1 9.0 a short circuit current v in = 2.75 v, v out = 0 v 6.0 8.5 a ripple rejection (note 3) v in = 3.25 v avg, v ripple = 1.0 v pp @ 120 hz, i out = 4.0 a, c adj = 0.1 m f; c out = 22 m f 60 80 db thermal regulation (note 3) 30 ms pulse, t a = 25 c 0.002 %/w dropout voltage (minimum v in v out ) (note 4) i out = 100 ma i out = 1.0 a i out = 2.75 a i out = 4.0 a i out = 8.0 a 0.92 0.93 0.94 0.95 0.96 1.15 1.15 1.15 1.15 1.30 v v v v v rms output noise freq = 10 hz to 10 khz, t a = 25 c 0.003 %v out temperature stability 0.5 % thermal shutdown (note 5) 150 180 210 c thermal shutdown hysteresis (note 5) 25 c 2. the minimum load current is the minimum current required to maintain regulation. normally the current in the resistor divider used to set the output voltage is selected to meet the minimum load current requirement. 3. this parameter is guaranteed by design and is not 100% production tested. 4. dropout voltage is defined as the minimum input/output voltage differential required to maintain 1.5% regulation. 5. this parameter is guaranteed by design, but not parametrically tested in production. however, a 100% thermal shutdown functio nal test is performed on each part.
cs52081 http://onsemi.com 3 package pin description package pin number to220 pin symbol function 1 adjust this pin is connected to the low side of the internally trimmed 1.5% bandgap reference voltage and carries a bias current of about 70 m a. a resistor divider from adj to v out and from adj to ground sets the output voltage. also, transient response can be improved by adding a small bypass capacitor from this pin to ground. 2 v out this pin is connected to the emitter of the power pass transistor and provides a regulated voltage capable of sourcing 8.0 a of current. 3 v in this is the supply voltage for the regulator. for the device to regulate, this voltage should be between 1.1 v and 1.30 v (depending on the output current) greater than the output voltage. figure 2. block diagram bias and tsd v ref + + ea ia v in v out adj typical performance characteristics 0 t j ( c) output current (a) figure 3. reference voltage vs. temperature figure 4. load regulation vs. output current 0 output voltage deviation (%) output voltage deviation (%) 0.100 0.075 0.050 0.025 0 0.025 0.050 0.075 0.100 0.125 0.150 0.250 0.225 0.200 0.175 0.150 0.125 0.100 0.075 0.050 0.025 0 10 20 30 40 50 60 70 80 90 100 110 120 130 1 2 3 4 5 6 7 8 t case = 0 c t case = 125 c t case = 25 c i o = 10 ma v in = 2.75 v
cs52081 http://onsemi.com 4 10 tcase ( c) i out (a) figure 5. adjust pin current vs. temperature figure 6. adjust pin vs. i out output current (a) v in v out (v) figure 7. dropout voltage vs. output current figure 8. short circuit vs. v in v out 72.6 0.8 adjust pin current ( m a) adjust pin current ( m a) 20 dropout voltage (v) output current (a) 1.25 0.5 v in v out (v) frequency (hz) figure 9. minimum load current vs. v in v out figure 10. ripple rejection vs. frequency minimum load current (ma) ripple rejection (db) 1 10 1 90 1.00 1 90 85 80 75 70 65 60 0 20 30 40 50 60 70 80 90 100 110 120 130 72.4 72.2 72.0 71.8 71.6 71.4 71.2 71.0 70.8 70.6 70.4 70.2 70 0.0 1.6 2.4 3.2 4.0 4.8 5.6 6.4 7.2 8.0 1.00 0.75 0.50 0.25 0 0 2345678 0.0 1.01.52.02.53.03.54.04.55.05.5 18 16 14 12 10 8 6 4 2 0 0.98 0.96 0.94 0.92 0.90 0.88 0.86 0.84 0.82 0.80 2345 10 2 10 3 10 4 10 5 10 6 80 70 60 50 40 30 20 10 t case = 0 c t case = 125 c t case = 25 c i o = 10 ma v in v out = 2.0 v v ripple = 1.0 v pp i out = 4.0 a c adj = 0.1 m f c out = 22 m f
cs52081 http://onsemi.com 5 application notes theory of operation the cs52081 linear regulator has a composite pnpnpn output stage that requires an output capacitor for stability. a detailed procedure for selecting this capacitor is included in the stability considerations section. adjustable operation design guidelines this ldo adjustable regulator has an output voltage range of 1.25 v to 4.5 v. an external resistor divider sets the output voltage as shown in figure 11. the regulator's voltage sensing error amplifier maintains a fixed 1.25 v reference between the output pin and the adjust pin. a resistor divider network r 1 and r 2 causes a fixed current to flow to ground. this current creates a voltage across r 2 that adds to the 1.25 v across r 1 and sets the overall output voltage. the adjust pin current (typically 50 m a) also flows through r 2 and adds a small error that should be taken into account if precise adjustment of v out is necessary. the output voltage is set according to the formula: v out v ref r 1 r 2 r 1 r 2 i adj the term i adj r 2 represents the error added by the adjust pin current. r 1 is chosen so that the minimum load current is at least 10 ma. r 1 and r 2 should be of the same composition for best tracking over temperature. the divider resistors should be placed as close to the ic as possible and connected to the output with a seperate metal trace. figure 11. v in cs52081 v out adj r 1 r 2 while not required, a bypass capacitor connected between the adjust pin and ground will improve transient response and ripple rejection. a 0.1 m f tantalum capacitor is recommended for afirst cuto design. value and type may be varied to optimize performance vs price. other adjustable operation considerations the cs52081 linear regulator has an absolute maximum specification of 6.0 v for the voltage dif ference between v in and v out . however, the ic may be used to regulate voltages in excess of 6.0 v. the main considerations in such a design are powerup and short circuit capability. in most applications, rampup of the power supply to v in is fairly slow, typically on the order of several tens of milliseconds, while the regulator responds in less than one microsecond. in this case, the linear regulator begins charging the output capacitor as soon as the v in to v out differential is large enough that the pass transistor conducts current. v out is essentially at ground, and v in is on the order of several hundred millivolts, so the pass transistor is in dropout. as v in increases, the pass transistor will remain in dropout, and current is passed to the load until v out is in regulation. further increase in v in brings the pass transistor out of dropout. the result is that the output voltage follows the power supply rampup, staying in dropout until the regulation point is reached. in this manner, any output voltage may be regulated. there is no theoretical limit to the regulated voltage as long as the v in to v out differential of 6.0 v is not exceeded. however, the maximum ratings of the ic will be exceeded in a short circuit condition. short circuit conditions will result in the immediate operation of the pass transistor outside of its safe operating area. overvoltage stresses will then cause destruction of the pass transistor before overcurrent or thermal shutdown circuitry can become active. additional circuitry may be required to clamp v in to v out differential to less than 6.0 v if failsafe operation is required. one possible clamp circuit is illustrated in figure 12; however, the design of clamp circuitry must be done on an application by application basis. care must be taken to ensure the clamp actually protects the design. components used in the clamp design must be able to withstand the short circuit conditions indefinitely while protecting the ic. figure 12. v in v out v adj external supply
cs52081 http://onsemi.com 6 stability considerations the output compensation capacitor helps determine three main characteristics of a linear regulator: startup delay, load transient response, and loop stability. the capacitor value and type is based on cost, availability, size and temperature constraints. a tantalum or aluminum electrolytic capacitor is best, since a film or ceramic capacitor with almost zero esr can cause instability. the aluminum electrolytic capacitor is the least expensive solution. however, when the circuit operates at low temperatures, both the value and esr of the capacitor will vary considerably. the capacitor manufacturer's data sheet provides this information. a 300 m f tantalum capacitor will work for most applications, but with high current regulators such as the cs52081 the transient response and stability improve with higher values of capacitance. the majority of applications for this regulator involve large changes in load current so the output capacitor must supply the instantaneous load current. the esr of the output capacitor causes an immediate drop in output voltage given by: v i esr for microprocessor applications it is customary to use an output capacitor network consisting of several tantalum and ceramic capacitors in parallel. this reduces the overall esr and reduces the instantaneous output voltage drop under transient load conditions. the output capacitor network should be as close to the load as possible for the best results. protection diodes when large external capacitors are used with a linear regulator it is sometimes necessary to add protection diodes. if the input voltage of the regulator gets shorted, the output capacitor will discharge into the output of the regulator. the discharge current depends on the value of the capacitor, the output voltage and the rate at which v in drops. in the cs52081 regulator, the discharge path is through a large junction and protection diodes are not usually needed. if the regulator is used with large values of output capacitance and the input voltage is instantaneously shorted to ground, damage can occur. in this case, a diode connected as shown in figure 13 is recommended. a rule of thumb useful in determining if a protection diode is required is to solve for current i c v t where: i is the current flow out of the load capacitance when v in is shorted, c is the value of the load capacitance, v is the output voltage, and t is the time duaration required for v in to transition from high to being shorted. if the calculated current is greater than or equal to the typical short circuit current value provided in the specifications, serious thought should be given to including a protection diode. figure 13. v in cs52081 v out adj current limit the internal current limit circuit limits the output current under excessive load conditions and protects the regulator. short circuit protection the device includes foldback short circuit current limit that clamps the output current at approximately two amperes less than its current limit value. thermal shutdown the thermal shutdown circuitry is guaranteed by design to become activated above a die junction temperature of 150 c and to shut down the regulator output. this circuitry includes a thermal hysteresis circuit with 25 c of typical hysteresis, thereby allowing the regulator to recover from a thermal fault automatically. calculating power dissipation and heat sink requirements high power regulators such as the cs52081 usually operate at high junction temperatures. therefore, it is important to calculate the power dissipation and junction temperatures accurately to ensure that an adequate heat sink is used. since the package tab is connected to v out on the cs52081, electrical isolation may be required for some applications. also, as with all high power packages, thermal compound is necessary to ensure proper heat flow. for added safety, this high current ldo includes an internal thermal shutdown circuit the thermal characteristics of an ic depend on the following four factors. junction temperature, ambient temperature, die power dissipation, and the thermal resistance from the die junction to ambient air. the maximum junction temperature can be determined by: t j(max) t a(max) p d(max) r ja
cs52081 http://onsemi.com 7 the maximum ambient temperature and the power dissipation are determined by the design while the maximum junction temperature and the thermal resistance depend on the manufacturer and the package type. the maximum power dissipation for a regulator is: p d(max) ( v in(max) v out(min) ) i out(max) v in(max) i in(max) a heat sink effectively increases the surface area of the package to improve the flow of heat away from the ic and into the surrounding air. each material in the heat flow path between the ic and the outside environment has a thermal resistance. like series electrical resistances, these resistances are summed to determine the total thermal resistance between the die junction and the surrounding air, r q jc . this total thermal resistance is comprised of three components. these resistive terms are measured from junction to case (r q jc ), case to heat sink (r q cs ), and heat sink to ambient air (r q sa ). the equation is: r ja r jc r cs r sa r q jc is rated @ 1.4 c/w for the cs52081. for a high current regulator such as the cs52081 the majority of heat is generated in the power transistor section. the value for r q sa depends on the heat sink type, while the r q cs depends on factors such as package type, heat sink interface (is an insulator and thermal grease used?), and the contact area between the heat sink and the package. once these calculations are complete, the maximum permissible value of r q ja can be calculated and the proper heat sink selected. for further discussion on heat sink selection, see application note athermal management,o document number and8036/d, available through the literature distribution center or via our website at http://onsemi.com.
cs52081 http://onsemi.com 8 package dimensions to220 three lead t suffix case 221a08 issue aa notes: 1. dimensioning and tolerancing per ansi y14.5m, 1982. 2. controlling dimension: inch. a k l g d n h q f 123 4 t seating plane s r j u t c 3 pl b y m b m 0.25 (0.010) y dim min max min max millimeters inches a 0.560 0.625 14.23 15.87 b 0.380 0.420 9.66 10.66 c 0.140 0.190 3.56 4.82 d 0.025 0.035 0.64 0.89 f 0.139 0.155 3.53 3.93 g 0.100 bsc 2.54 bsc h --- 0.280 --- 7.11 j 0.012 0.045 0.31 1.14 k 0.500 0.580 12.70 14.73 l 0.045 0.060 1.15 1.52 n 0.200 bsc 5.08 bsc q 0.100 0.135 2.54 3.42 r 0.080 0.115 2.04 2.92 s 0.020 0.055 0.51 1.39 t 0.235 0.255 5.97 6.47 u 0.000 0.050 0.00 1.27 v v 0.045 --- 1.15 --- package thermal data parameter to220 three lead unit r q jc typical 1.4 c/w r q ja typical 50 c/w on semiconductor and are registered trademarks of semiconductor components industries, llc (scillc). scillc reserves the right to mak e changes without further notice to any products herein. scillc makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does scillc assume any liability arising out of the application or use of any product or circuit, and s pecifically disclaims any and all liability, including without limitation special, consequential or incidental damages. atypicalo parameters which may be provided in scillc data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. all operating parameters, including atypicalso must be validated for each customer application by customer's technical experts. scillc does not convey any license under its patent rights nor the rights of others. scillc products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body , or other applications intended to support or sustain life, or for any other application in which the failure of the scillc product could create a sit uation where personal injury or death may occur. should buyer purchase or use scillc products for any such unintended or unauthorized application, buyer shall indem nify and hold scillc and its of ficers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and re asonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized u se, even if such claim alleges that scillc was negligent regarding the design or manufacture of the part. scillc is an equal opportunity/affirmative action employ er. publication ordering information japan : on semiconductor, japan customer focus center 4321 nishigotanda, shinagawaku, tokyo, japan 1410031 phone : 81357402700 email : r14525@onsemi.com on semiconductor website : http://onsemi.com for additional information, please contact your local sales representative. cs52081/d literature fulfillment : literature distribution center for on semiconductor p.o. box 5163, denver, colorado 80217 usa phone : 3036752175 or 8003443860 toll free usa/canada fax : 3036752176 or 8003443867 toll free usa/canada email : onlit@hibbertco.com n. american technical support : 8002829855 toll free usa/canada
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