rev. 10/2/00 as2810 1a low dropout voltage regulator adjustable & fixed output, fast response features applications ? adjustable output down to 1.2v ? scsi-ii active terminator ? fixed output voltages 1.5v, 2.5v, 3.0v, 3.3v, 5.0v ? portable palmtap/notebook computer ? output current of 1a ? smps post-regulator ? low dropout voltage 1.2v typ. ? disk drives ? extremely tight load and line regulation ? portable consumer equipment ? current & thermal limiting ? portable instrumentation ? standard 3-terminal low cost to-220, to-263, to-252 & sot-223 ? battery charger product description the as2810 is a low power positive voltage regulator designed to meet 1a output current and comply with scsi-ii specifications with fix output voltage of 2.85v. this device is an excellent choice for use in battery-powered applications and portable computers . the as2810 features very low quiescent current and very low dropout voltage of 1.2v at a full load and lower as output current decr eases. this product is available as adjustable or fixed 1.5v, 2.5v, 3.0v, 3.3v, and 5v output voltages. the as2810 is offered in a 3-pin surface mount packages sot-223, to-220, to-252 & dd package. the output capacitor of 10 f or larger is needed for the output stability of as2810 as required by most other regulator circuits ordering information to-220 3-pin dd plastic 3-pin sot-223 3-pin to-252 3-pin opeperating junction temp. range AS2810YU-X as2810yt-x as2810ym3-x as2810yr-x -45 to +125 c x= output voltage (1.5v, 2.5v, 3.0v, 3.3v, 5.0v and blank for adj.) y= output tolerance, a for 1% blank for 2% consult with factory for other fixed voltages. pin connections front view to-220-3 (u) as2810 1 23 adj/gnd v out v in top view to-263-3 (t) 1 as2810 2 3 adj/gnd v out v in front view to-252 (r) adj/gnd v in v out 3 2 1 as2810 top view sot-223 (m3) adj/ gnd v out v in as2810 13 2
rev. 10/2/00 as2810 absolute maximum ratings lead temp. (soldering, 10 seconds) .............................. 300c input voltage........................................... ............. 10v storage temperature range ............................ -65 to +150c input to output voltage differential .................... 10v operating junction temperature range ...................... as2810 control section ............................ -45c +125c as2810 power transistor...........................-45c +150c electrical characteristics (note 1) at i out = 10ma, t a =25 c, unless otherwise specified. parameter conditions typ as2810a as2810 units min max min max 1.5v version 1.485 1.515 1.470 1.530 output voltage (note 2) as2810-1.5v, 0 < i out < 1a, 3.3v rev. 10/2/00 as2810 electrical characteristics (cont.) long term stability t a =125oc, 1000 hrs. 0.3 (note 2) 1 1 % thermal regulation ( ? v out (pwr)) t a =25oc, 20 ms pulse 0.01 0.020 0.020 %/w temperature stability ( ? v out (t)) 0.25 % output noise, rms 10hz to 10khz t a =25oc 0.003 % vo 3.0 3.0 to-220 junction to tab junction to ambient 60 60 3.0 3.0 dd package junction to tab junction to ambient 60 60 15 15 thermal resistance sot-223 package junction to tab junction to ambient 156 156 the bold specifications apply to the full operating temperature range. note 1: changes in output voltage due to heating effects are covered under the specification for thermal regulation. note 2: fixed version only note 3: adjustable version only oc/w
rev. 10/2/00 as2810 application hints the as2810 incorporates protection against over-current faults, reversed load insertion, over temperature operation, and positive and negative transient voltage. however, the use of an output capacitor is required in order to improve the stability and the performances. stability the output capacitor is part of the regulator?s frequency compensation system. either a 22 f aluminum electrolytic capacitor or a 10 f solid tantalum capacitor between the output terminal and ground guarantees stable operation for all operating conditions. however, in order to minimize overshoot and undershoot, and therefore optimize the design, please refer to the section ?ripple rejection?. ripple rejection ripple rejection can be improved by adding a capacitor between the adj pin and ground as shown in figure 6. when adj pin bypassing is used, the value of the output capacitor required increases to its maximum (22 f for an aluminum electrolytic capacitor, or 10 f for a solid tantalum capacitor). if the adj pin is not bypass, the value of the output capacitor can be lowered to 10 f for an electrolytic aluminum capacitor or 4.7 f for a solid tantalum capacitor. however the value of the adj-bypass capacitor should be chosen with respect to the following equation: c = 1 / ( 6.28 * f r * r 1 ) where c = value of the capacitor in farads (select an equal or larger standard value), f r = ripple frequency in hz, r 1 = value of resistor r 1 in ohms. if an adj-bypass capacitor is use, the amplitude of the output ripple will be independent of the output voltage. if an adj- bypass capacitor is not used, the output ripple will be proportional to the ratio of the output voltage to the reference voltage: m = v out / v ref where m = multiplier for the ripple seen when the adj pin is optimally bypassed. v ref = reference voltage reducing parasitic resistance and inductance one solution to minimize parasitic resistance and inductance is to connect in parallel capacitors. this arrangement will improve the transient response of the power supply if your system requires rapidly changing current load condition. thermal consideration although the as 2810 offers some limiting circuitry for overload conditions, it is necessary not to exceed the maximum junction temperature, and therefore to be careful about thermal resistance. the heat flow will follow the lowest resistance path, which is the junction-to-case thermal resistance. in order to insure the best thermal flow of the component, a proper mounting is required. note that the case of the device is electrically connected to the output. in case the case has to be electrically isolated, a thermally conductive spacer can be used. however do not forget to consider its contribution to thermal resistance. assuming: v in = 10v, v out = 5v, i out = 1.5a, t a = 50 c/w, heatsink case = 6 c/w, heatsink case = 0.5 c/w, jc = 3 c/w power dissipation under this condition p d = (v in ? v out ) * i out = 7.5w junction temperature t j = t a + p d * ( case - hs + hs + jc ) for the control sections t j = 50 + 7.5*(0.5+6=3) = 121.25 c 121.25 c < t j (max) for the control & power sections. in both case reliable operation is insured by adequate junction temperature.
rev. 10/2/00 as2810 basic adjustable regulator output voltage consider figure 2. the resistance r 1 generates a constant current flow, normally the specified load current of 10ma. this current will go through the resistance r 2 to set the overall output voltage. the current i adj is very small and constant. therefore its contribution to the overall output voltage is very small and can generally be ignored. load regulation parasitic line resistance can degrade load regulation. in order not to affect the behavior of the regulator, it is best to connect directly the r 1 resistance from the resistor divider to the case, and not to the load. for the same reason, it is best to connect the resistor r 2 to the negative side of the load. output voltage the fixed voltage ldo voltage regulator are simple to use regulators since the v out is preset to the specifications. it is important however, to provide the proper output capacitance for stability and improvement. for most operating conditions a capacitance of 22uf tantalum or 100uf electrolytic will ensure stability and prevent oscillation. as2810 fig.2 basic adjustable regulator v in v ref v out = v ref * ( 1 + r 2 /r 1 ) + i adj * r 2 i adj 50a v out r 2 r 1 as2810 fig.3 basic adjustable regulator v in r 2 r 1 connect r 2 to load r l connect r 1 to case of regulator r p parasitic line resistance as2810 basic fixed regulator v in v out 5v c1 10uf c2 10uf 3.3v
rev. 10/2/00 as2810 typical applications in out adj as2810 c 1 r 1 v out fig. 5 typical adjustable regulator v in load adj as2810 fig. 4 1a current output regulator v in c 1 out in r 2 c 2 v out = v ref (1 + r 2 ) + i adj r 2 r 1 r 1 note a: v in(min) = (intended v out ) + (v dropout (max) ) as2810 fig. 6 improving ripple rejection v in r 1 r 2 150f 10f* 121? 1% 365? 1% + + 10f c 1 *c 1 improves ripple rejection. xc should be ~ r 1 at ripple frequency. 5v adj in out (note a) v out as2810 fig.7 5v regulator with shutdown v in 100f 121? 1% 365? 1% + + 10f 5v adj in out (note a) 1k 1k ttl input 2n3904 note a: v in(min) = (intended v out ) + (v dropout (max) )
rev. 10/2/00 as2810 typical characteristics
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