iru1015 1 rev. 1.3 08/20/02 www.irf.com typical application description the iru1015 is a low dropout three-terminal adjustable regulator with minimum of 1.5a output current capabil- ity. this product is specifically designed to provide well regulated supply for low voltage ic applications such as 486dx4 processor, p55c ? i/o supply as well as high speed bus termination and low current 3.3v logic sup- ply. the iru1015 is also well suited for other applica- tions such as vga and sound card. the iru1015 is guaranteed to have <1.3v dropout at full load current making it ideal to provide well regulated outputs of 2.5v to 3.3v with 4.75v to 7v input supply. 1.5a low dropout positive adjustable regulator figure 1 - typical application of iru1015 in a 5v to 3.3v regulator. t j (c) 2-pin plastic 3-pin plastic 3-pin plastic to-252 (d-pak) to-263 (m) to-220 (t) 0 to 150 IRU1015CD iru1015cm iru1015ct data sheet no. pd94122 package order information note: p55c is trademark of intel corp. guaranteed < 1.3v dropout at full load current fast transient response 1% voltage reference initial accuracy output current limiting built-in thermal shutdown features applications 486dx4 supply voltage p55 i/o supply voltage vga & sound card applications low voltage high speed termination applications standard 3.3v chip set and logic applications c2 1500uf 5v 3.3v / 1.5a r1 121 r2 200 c1 1500uf iru1015 1 2 3 adj v in v out
iru1015 2 rev. 1.3 08/20/02 www.irf.com absolute maximum ratings input voltage (v in ) .................................................... 7v power dissipation ..................................................... internally limited storage temperature range ...................................... -65c to 150c operating junction temperature range ..................... 0c to 150c package information 2-pin plastic to-252 (d-pak ) 3-pin plastic to-263 (m) 3-pin plastic to-220 (t) electrical specifications unless otherwise specified, these specifications apply over c in =1 m f, c out =10 m f, and t j =0 to 150 8 c. typical values refer to t j =25 8 c. note 3: minimum load current is defined as the mini- mum current required at the output in order for the out- put voltage to maintain regulation. typically the resistor dividers are selected such that it automatically main- tains this current. adj v in v out 1 2 3 front view tab is v out adj v in 1 3 front view tab is v out reference voltage line regulation load regulation (note 1) dropout voltage (note 2) current limit minimum load current (note 3) thermal regulation ripple rejection adjust pin current adjust pin current change temperature stability long term stability rms output noise parameter sym test condition min typ max units q ja =70 c/w for 0.5" square pad q ja =35 c/w for 1" square pad q jt =2.7 c/w q ja =60 c/w io=10ma, t j =25 8 c, (v in -vo)=1.5v io=10ma, (v in -vo)=1.5v io=10ma, 1.3v<(v in -vo)<7v v in =3.3v, v adj =0, 10ma iru1015 3 rev. 1.3 08/20/02 www.irf.com application information introduction the iru1015 adjustable low dropout (ldo) regulator is a three-terminal device which can easily be programmed with the addition of two external resistors to any volt- ages within the range of 1.25 to 5.5 v.this regulator un- like the first generation of the three-terminal regulators such as lm117 that required 3v differential between the input and the regulated output, only needs 1.3v differen- tial to maintain output regulation. this is a key require- ment for today?s microprocessors that need typically 3.3v supply and are often generated from the 5v sup- ply. another major requirement of these microproces- sors is the need to switch the load current from zero to full load in tens of nanoseconds at their pins, which translates to an approximately 300 to 500ns current step at the regulator. in addition, the output voltage toler- ances are sometimes tight and they include the tran- sient response as part of the specification. the iru1015 is specifically designed to meet the fast current transient needs as well as provide an accurate initial voltage, reducing the overall system cost with the need for fewer output capacitors. figure 2 - simplified block diagram of the iru1015. block diagram pin # pin symbol pin description pin descriptions a resistor divider from this pin to the v out pin and ground sets the output voltage. the output of the regulator. a minimum of 10 m f capacitor must be connected from this pin to ground to insure stability. the input pin of the regulator. typically a large storage capacitor is connected from this pin to ground to insure that the input voltage does not sag below the minimum drop out voltage during the load transient response. this pin must always be 1.3v higher than v out in order for the device to regulate properly. 1 2 3 adj v out v in v in 3 1 adj 2 v out thermal shutdown current limit 1.25v + +
iru1015 4 rev. 1.3 08/20/02 www.irf.com v out r1 r2 v in v ref i adj = 50ua iru1015 adj v out v in r1 r2 v in r l r p parasitic line resistance iru1015 adj v out v in output voltage setting the iru1015 can be programmed to any voltages in the range of 1.25v to 5.5v with the addition of r1 and r2 external resistors according to the following formula: where: v ref = 1.25v typically i adj = 50 m a typically r1 and r2 as shown in figure 3: figure 3 - typical application of the iru1015 for programming the output voltage. the iru1015 keeps a constant 1.25v between the out- put pin and the adjust pin. by placing a resistor r1 across these two pins a constant current flows through r1, add- ing to the i adj current and into the r2 resistor producing a voltage equal to the (1.25/r1) 3 r2 + i adj 3 r2 which will be added to the 1.25v to set the output voltage. this is summarized in the above equation. since the mini- mum load current requirement of the iru1015 is 10ma, r1 is typically selected to be 121 v resistor so that it automatically satisfies the minimum current requirement. notice that since i adj is typically in the range of 50 m a it only adds a small error to the output voltage and should only be considered when a very precise output voltage setting is required. for example, in a typical 3.3v appli- cation where r1=121 v and r2=200 v the error due to i adj is only 0.3% of the nominal set point. load regulation since the iru1015 is only a three-terminal device, it is not possible to provide true remote sensing of the output voltage at the load. figure 4 shows that the best load regulation is achieved when the bottom side of r2 is connected to the load and the top side of r1 resistor is connected directly to the case or the v out pin of the regulator and not to the load. in fact, if r1 is connected v out = v ref 3 1+ +i adj 3 r2 r2 r1 ( ) to the load side, the effective resistance between the regulator and the load is gained up by the factor of (1+ r2/r1),or the effective resistance will be r p(eff) =r p 3 (1+ r2/r1). it is important to note that for high current appli- cations, this can represent a significant percentage of the overall load regulation and one must keep the path from the regulator to the load as short as possible to minimize this effect. figure 4 - schematic showing connection for best load regulation. stability the iru1015 requires the use of an output capacitor as part of the frequency compensation in order to make the regulator stable. typical designs for microprocessor ap- plications use standard electrolytic capacitors with a typical esr in the range of 50 to 100m v and an output capacitance of 500 to 1000 m f. fortunately as the ca- pacitance increases, the esr decreases resulting in a fixed rc time constant. the iru1015 takes advantage of this phenomena in making the overall regulator loop stable. for most applications a minimum of 100 m f alu- minum electrolytic capacitor such as sanyo mvgx se- ries, panasonic fa series as well as the nichicon pl series insures both stability and good transient response. thermal design the iru1015 incorporates an internal thermal shutdown that protects the device when the junction temperature exceeds the maximum allowable junction temperature. although this device can operate with junction tempera- tures in the range of 150 8 c, it is recommended that the selected heat sink be chosen such that during maxi- mum continuous load operation the junction tempera- ture is kept below this number. the example below shows the steps in selecting the proper regulator heat sink for an amd 486dx4-120 mhz processor.
iru1015 5 rev. 1.3 08/20/02 www.irf.com v in = 5v v out = 3.45v i out(max) = 1.2a t a = 35 8 c note: for further information regarding the above com- panies and their latest product offerings and application support contact your local representative or the num- bers listed below: aavid thermalloy...............ph# (603) 528-3400 designing for microprocessor applications as it was mentioned before the iru1015 is designed specifically to provide power for the new generation of the low voltage processors requiring voltages in the range of 2.5v to 3.6v generated by stepping down the 5v sup- ply. these processors demand a fast regulator that sup- ports their large load current changes. the worst case current step seen by the regulator is anywhere in the range of 1 to 7a with the slew rate of 300 to 500ns which could happen when the processor transitions from ?stop clock? mode to the ?full active? mode. the load current step at the processor is actually much faster, in the or- der of 15 to 20ns, however, the de-coupling capacitors placed in the cavity of the processor socket handle this transition until the regulator responds to the load current levels. because of this requirement, the selection of high frequency low esr and low esl output capacitor is im- perative in the design of these regulator circuits. figure 5 shows the effects of a fast transient on the output voltage of the regulator. as shown in this figure, the esr of the output capacitor produces an instanta- neous drop equal to the ( d v esr =esr 3 d i) and the esl effect will be equal to the rate of change of the output current times the inductance of the capacitor ( d v esl =l 3 d i/ d t). the output capacitance effect is a droop in the output voltage proportional to the time it takes for the regulator to respond to the change in the current ( d v c = d t 3 d i/c ) where d t is the response time of the regulator. air flow (lfm) 0 100 thermalloy 6041pb no hs required aavid 574602 no hs required assuming the following specifications: the steps for selecting a proper heat sink to keep the junction temperature below 135 c is given as: 1) calculate the maximum power dissipation using: 2) select a package from the regulator data sheet and record its junction to case (or tab) thermal resistance. selecting to-220 package gives us: 3) assuming that the heat sink is black anodized, cal- culate the maximum heat sink temperature allowed: assume, u cs=0.05 c/w (heat-sink-to-case thermal resistance for black anodized) 4) with the maximum heat sink temperature calculated in the previous step, the heat-sink-to-air thermal re- sistance ( u sa ) is calculated by first calculating the temperature rise above the ambient as follows: 5) next, a heat sink with lower q sa than the one calcu- lated in step 4 must be selected. one way to do this is to simply look at the graphs of the "heat sink temp rise above the ambient" vs. the "power dissipation" and select a heat sink that results in lower tempera- ture rise than the one calculated in the previous step. the following heat sinks from aavid and thermalloy meet this criteria. p d = i out 3 (v in - v out ) p d = 1.2 3 (5 - 3.45) = 1.86w u jc = 2.7 8 c/w t s = t j - p d 3 ( u jc + u cs ) t s = 135 - 1.86 3 (2.7 + 0.05) = 129 8 c u sa = = = 50 8 c/w 94 1.86 d t p d d t = t s - t a = 129 - 35 = 94 8 c d t = temperature rise above ambient
iru1015 6 rev. 1.3 08/20/02 www.irf.com v esr v esl v c t load current load current rise time 1015plt1-1.0 c in = = 400 m f 1.2 3 50 0.15 esr = = 0.167 v (5 - 3.45 - 1.2 - 0.15) 1.2 esr = (v in - v out - d v - v drop ) d i d vc = = = 1.6mv d t 3 d i 2 3 1.2 c 1500 esr [ = 45m v 54 1.2 type of v out i max max allowed processor nominal output tolerance amd 486dx4 3.45 v 1.2 a 150 mv 2) with the output capacitance being 1500 m f: where: d t = 2 m s is the regulator response time to set the output voltage, we need to select r1 and r2: 3) assuming r1=121 v , 1% select r2 = 215 v , 1% selecting both r1 and r2 resistors to be 1% toler- ance results in the least amount of error introduced by the resistor dividers leaving a ? 2.5% error bud- get for the iru1015 reference which is well within the initial accuracy of the device. finally, the input capacitor is selected as follows: 4) assuming that the input voltage can drop 150mv be- fore the main power supply responds, and that the main power supply response time is ? 50ms, then the minimum input capacitance for a 1.2a load step is given by: the esr should be less than: where: v drop l input voltage drop allowed in step 4 d v l maximum regulator dropout voltage d i l load current step select a single 1500 m f the same type as the output capacitors exceeds our requirements. figure 6 shows the completed schematic for our example. figure 5 - typical regulator response to the fast load current step. an example of a regulator design to meet the amd speci- fication for 486dx4-120mhz is given below. assume the specification for the processor as shown in table 1: table 1 - gtl+ specification for pentium pro the first step is to select the voltage step allowed in the output due to the output capacitor?s esr: 1) assuming the regulator?s initial accuracy plus the re- sistor divider tolerance is ? 86mv (2.5% of 3.45v nominal), then the total step allowed for the esr and the esl, is -64mv. assuming that the esl drop is -10mv, the remaining esr step will be -54mv. therefore the output ca- pacitor esr must be: the sanyo mvgx series is a good choice to achieve both price and performance goals. the 6mv1500gx, 1500 m f, 6.3v has an esr of less than 36m v typi- cal. selecting a single capacitor achieves our design goal. the next step is to calculate the drop due to the ca- pacitance discharge and make sure that this drop in voltage is less than the selected esl drop in the previous step. r2 = 3 r1 = 3 121 = 213 v v out v ref -1 ( ) 3.45 1.25 -1 ( )
iru1015 7 rev. 1.3 08/20/02 www.irf.com layout consideration the output capacitors must be located as close to the v out terminal of the device as possible. it is recom- mended to use a section of a layer of the pc board as a plane to connect the v out pin to the output capacitors to prevent any high frequency oscillation that may result from excessive trace inductance. figure 6 - final schematic for the regulator design. ir world headquarters: 233 kansas st., el segundo, california 90245, usa tel: (310) 252-7105 tac fax: (310) 252-7903 visit us at www.irf.com for sales contact information data and specifications subject to change without notice. 02/01 3.45v r1 121 1% r2 215 1% 5v c2 1500uf c1 1500uf iru1015 adj v out v in
iru1015 8 rev. 1.3 08/20/02 www.irf.com (d) to-252 package 2-pin symbol a b c d e f g h j k l m n o p q r r1 s min 6.477 5.004 0.686 7.417 9.703 0.635 4.521 & 1.52 2.184 0.762 1.016 5.969 1.016 0 0.534 0.428 max 6.731 5.207 0.838 8.179 10.084 0.889 4.623 & 1.62 2.388 0.864 1.118 6.223 1.118 0.102 0.686 0.588 note: all measurements are in millimeters. a b c d f g h 45 8 k m q 7 8 n p r s r1 l c e j l o r0.31 typ r0.51 typ 2.286 bsc
iru1015 9 rev. 1.3 08/20/02 www.irf.com (m) to-263 package 3-pin symbol a b c d e g h k l m n p r s u v min 10.05 8.28 4.31 0.66 1.14 14.73 1.40 0.00 2.49 0.33 2.286 0 8 2.41 max 10.312 8.763 4.572 0.91 1.40 15.75 1.68 0.254 2.74 0.58 2.794 8 8 2.67 6.50 ref 7.75 ref 2.54 ref note: all measurements are in millimeters. a e m l n u c b k p v r s h g d c l
iru1015 10 rev. 1.3 08/20/02 www.irf.com (t) to-220 package 3-pin symbol a a b b1 c1 cp d e e e1 e3 f h1 j1 l q r min 4.06 3 8 0.63 1.14 0.38 3.71d 14.22 9.78 2.29 4.83 1.14 1.14 5.94 2.29 13.716 2.62 5.588 max 4.83 7.5 8 1.02 1.52 0.56 3.96d 15.062 10.54 2.79 5.33 1.40 1.40 6.55 2.92 14.22 2.87 6.17 note: all measurements are in millimeters. e-pin cp c1 j1 f a a (5x) q e b e3 b1 e1 l h1 e d r l c c l
iru1015 11 rev. 1.3 08/20/02 www.irf.com pkg desig d m t package description to-252, (d-pak) to-263 to-220 parts per tube 75 50 50 parts per reel 2500 750 --- package shipment method pin count 2 3 3 t & r orientation fig a fig b --- feed direction figure a feed direction figureb 1 1 1 1 1 1 ir world headquarters: 233 kansas st., el segundo, california 90245, usa tel: (310) 252-7105 tac fax: (310) 252-7903 visit us at www.irf.com for sales contact information data and specifications subject to change without notice. 02/01
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