date: 5/14/04 spx1581 5a ultra low dropout voltage regulator fast response, adjustable & fixed features applications ? low dropout voltage 500mv at 5a full load current ? 3.3v to 2.8v atx power supplies ? adjustable output down to 1.2v from atx power supply ? 3.3v to 2.9v for portable pentium ? ? ? ? processor ? fixed output voltages of 3.3v, 2.8v & 2.5v ? 5v to 3.5v vre supply ? extremely tight voltage and line regulation ? high efficiency ?green? computer systems ? standard 5-terminal low cost to-220 & to-263 product description the spx1581 is a 5a low dropout regulator with extremely low dropout voltage. the adjustable version requires only two externa l resistors to set the output voltage. the fixed version has a preset output of 3.3v, 2.8v or 2.5v and does not require any exte rnal resistors. the spx1581 features a low dropout of less than 400mv(typ.) and offers fast transient response. this device is suitable for pentium applications requiring 2.8v or 2.5v from 3.3v atx power supplies, where a low current input voltage 1v greater than the output voltage is needed. with an external sense pin the load regulation is less than 1mv. this device is an excelle nt choice for the use in powering low voltage microprocessors that require a lower dropout, fast transient response to regulate from 3.3v and 5v supplies. the spx1581 is also an excellent choice as a post regulator for switching supplies applications. the spx1581 offers full protection against over-current faults, reversed input polarity, over temperature operation and positiv e and negative transient voltage. the spx1581 is offered in a 5 pin to-220 and to-263 compatible with industry standard 5-terminal regulators. for 7a, 3a and 1. 5a ultra low dropout versions refer to spx1580, spx1582 and spx1583 data sheets respectively. to-263-5 (t) top view 45 spx1581 12 3 1. sense 2. adj or fixed 3. v out 4. v ctrl 5. v in to-220-5 (u) front view 5 4 3 2 1 spx1581 1. sense 2. adj or fixed 3. v out 4. v ctrl 5. v in pin connections
date: 5/14/04 spx1581 absolute maximum ratings power dissipation.................................................... internally limited input supply voltage ................... .......................................6v lead temp (soldering, 10 seconds)........................................... 300 c v ctrl input voltage ..........................................................13v storage temperature range ...................................... -65oc to +150oc operating junction temperature range spx1581 control section .............................................0oc to +125oc spx1581 power transistor .......................................... 0oc to +150oc electrical characteristics at v s =14v, ta=25 c, io=10ma, c2=100 f, unless otherwise specified. (note 1) (boldface applies over full temperature range). parameters conditions spx1581 min typ max units 2.5v version output voltage v ctrl =6.0v to 12v, v in =3.0v to 5.0v, i o =10ma i o =10ma to 5a 2.450 2.400 2.500 2.550 2.600 v 2.8v version output voltage v ctrl =6.3v to 12v, v in =3.3v to 12v, i o =10ma i o =10ma to 5a 2.744 2.688 2.800 2.856 2.912 v 3.3v version output voltage v ctrl =6.3v to 12v, v in =3.3v to 12v, i o =10ma i o =10ma to 5a 3.234 3.168 3.300 3.366 3.462 v all voltage options reference voltage v ctrl =2.75v, v in =2.00v, i o =10ma v ctrl =2.7v to 12v, v in =2.05v to 5.5v, i o =10ma to 5a 1.238 1.250 1.263 v line regulation v ctrl =2.5v to 12v, v in =1.75v to 5.5v, i o =10ma v adj =0v 1.0 3.0 mv load regulation (note1) v ctrl =2.75v, v in =2.1v, i o =10ma to 5a,v adj =0v 1.0 5.0 mv dropout voltage minimum v ctrl (note2) (v ctrl ? v out ) v adj =0v v in =2.05v, i o =1a 1.10 1.25 v dropout voltage minimum v in (note2) (v in - v out ) v adj =0v v in =2.75v, i o =5a 0.40 0.50 v current limit v ctrl =2.75v, v in =2.05v,dv o =100mv,v adj =0v 5.1 a minimum load current v ctrl =5v, v in =3.3v,v adj =0v 5 10 ma thermal regulation 30ms pulse 0.002 0.02 %w ripple rejection v ctrl =3.75v v in =3.75v, i o =2.5a,v adj =0v t j =25, v ripple =1vpp at 120hz 60 80 db control pin current v adj =0v v ctrl =2.75v, v in =2.05v, i o =5a 60 120 ma adjustable pin current v ctrl =2.75v, v in =2.05v,v adj =0v i o =10ma 50 120 a junction to case ( jc ) 3 c/w to-220-5 junction to ambient ( ja ) 50 c/w junction to case ( jc ) 3 c/w thermal resistance to-263-5 junction to ambient ( ja ) 60 c/w the bold specifications applying to the over full operating temperature range. note 1: low duty cycle pulse testing with kelvin connections are required to order to maintain accurate data. note 2: dropout voltage is defined as the minimum differential between v in and v out or v ctrl and v out required to maintain regulation at v out 99% nominal v out. note 3: v ref is measured across the adjust pin to sense pin.
date: 5/14/04 spx1581 block diagram applications notes the spx1581 is designed as a high performance and low cost solution for application requiring a lower dropout than traditional npn regulators. the spx1581 uses a separate input voltage v ctrl (v ctrl v out + 1.3v) to minimize the dropout voltage. this allows the 2.5v power for the load to come from a 3.3v system supply. as added benefit this will reduce the heat dissipation, and lower heatsink and cooling fan cost. a typical application would use 5v for vin and 3.3v for v ctrl from a motherboard power supply to provide a nominal 2.5v output. using the sense pin allows to kelvin measure the output, reducing resistive-associated errors. the spx1581 can power the 2.5v core voltage for microprocessors such as pentium , p55c , amd5k86 and k6 and the ibm powerpc 603ev and 604ev processors. *the reduction of heat dissipation is a result of the increase of the regulator efficiency (efficiency = v out / v in ). adjustable regulator design 1.25v reference voltage is being developed between the sense pin and the adj pin of the spx1581. adding two external resistors (see fig 1.) will allow setting the output voltage from 1.25v to 6v. r 1 is chosen so that this current is specified minimum load current of 10ma. r 2 is given by the formula: v out = v ref (1+ r 2 /r 1 ) + i adj (r 2 ). the current flowing from the adj pin is typically 50 a. this adj pin contributes to the final vout but is usually neglected. connecting the sense pin to the top of the resistor divider will improve load regulation. lowering noise using the sense pin to kelvin the load will increase accuracy of the output voltage during load regulation. for the fixed voltage devices, adding a capacitor at the gnd pin will improve transient response. this capacitor is chosen in the range of 1 f to 0.1 f and will depend on the amount of output capacitance in the system. pin description 1. sense = allows kelvin sense of v out at the load. (positive side of the reference voltage of the device). 2. adj = negative side of the reference voltage for the device. adding a small bypass capacitor from the adj pin to ground will improve the transient response. 3. v out = power output of the device. 4. v ctrl = supply pin for the control circuitry of the device. the current flow into this pin will be about 1% of the output current. v ctrl must be between 1.0v and 1.3v greater than the output voltage for the device to regulate. 5. v in = output load current is supplied through this pin. v in must be between 0.1v and 0.8v greater than the output voltage for the device to regulate. (4) v ctrl v in (5) s.o.a v out (3) limit sense current limit amplifier thermal overload voltage regulation amplifier v ref sense (1) adj (2)
date: 5/14/04 spx1581 typical application spx1581 sense adj v in v ctrl r1 124 c4 2 x 330uf c2 10uf c1 330uf 5v v ctrl 3.3v v in c3 .033uf (1) v ctrl needed when v in < 5v. (2) v out = v ref (1 + r2/ r1) + i adj r2. (3) v ref is measured across adjust to sense. 2.5v v out ? r2 124 ? v out fig. 1 adjustable regulator spx1581 sense gnd v in v ctrl c4 2 x 330uf c2 10uf c1 330uf 5v v ctrl 3.3v v i n (1) v ctrl is needed when v in <5v. fig.2 typical fixed regulator 2.5v v out v out
date: 5/14/04 spx1581 ordering information ordering no. precision output voltages packages spx1581u 0.6% a dj 5 lead to-220 spx1581u-2.5 0.6% 2.5v 5 lead to-220 spx1581u-2.8 0.6% 2.8v 5 lead to-220 spx1581u-3.3 0.6% 3.3v 5 lead to-220 spx1581t 0.6% a dj 5 lead to-263 spx1581t-2.5 0.6% 2.5v 5 lead to-263 spx1581t-2.8 0.6% 2.8v 5 lead to-263 spx1581t-3.3 0.6% 3.3v 5 lead to-263 analog excellen ce sipex corporation headquarters and main offices: 233 south hillview drive milpitas, ca 95035 tel: (408) 935-7600 fax: (408) 934-7500 sipex corporation reserves the right to make changes to any products described herein. sipex does not assume any liab ility arising out of the application or use of any pr oduct or circuit described hereing; neither does it convey any license under its patent rights nor the rights of others. corporation
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