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rev. 9/29/00 x= output voltages (3.0v, 3.3v and 5.0v) as2950/as2951 150ma low dropout voltage regulators features applications ? 5.0v, 3.3v, and 3.0v versions at 150ma output ? battery powered systems ? very low quiescent current ? cordless telephones ? low dropout voltage ? radio control systems ? extremely tight load and line regulation ? portable/palm top/notebook computers ? very low temperature coefficient ? portable consumer equipment ? needs only 1 f for stability ? portable instrumentation ? current & thermal limiting ? avionics ? unregulated dc input can withstand -20v reverse battery ? automotive electronics and +60v positive transients ? smps post-regulator ? similar replacement with higher i out for lp2950/lp2951 sockets ? voltage reference as2951 versions only ? error flag warns of output dropout ? logic-controlled electronic shutdown ? output programmable from 1.24v to 29v product description the as2950 and as2951 are low power voltage regulators. these devices are an excellent choice for use in battery-powered applications such as cordless telephones, radio control systems, and portable computers. the as2950 and as2951 feature very lo w quiescent current and very low dropout voltage (typ. 50mv at light load and 380mv at 100ma). this include a tight initial tole rance of 0.5% typ., extremely good load and line regulation of 0.05% typ. and very low output temperature coefficient, making the as2950/as2951 useful as a low-power voltage reference. other key additional features of this device includes higher output cur rent (150ma), positive transient protection up to 60v (load dump), and the ability to survive an unregulated input voltage transient of - 20v below ground (reverse battery). the error flag output feature is used as power-on reset for warning of a low output voltage, due to falling voltage input of ba tteries. another feature is the logic-compatible shutdown input which enables the regulator to be switched on and off. the as2950 is offered in a 3-pin to-92 package compatible with other 5v regulators. the as2951 is also available in 8-pin plastic, so-8 and to-99 metal can packages. the regulator output voltage may be pin-strapped for a 5v, 3.3v and 3.0v or programmed from 1.24v to 29v with an external pair of resistors. look for as2954 for 250ma and as2955 for 350ma. ordering information to-92 3-pin soic 8-pin oper. temp. range as2950acn-x -40 c to +125 c as2950cn-x -40 c to +125 c as2951acs-x -40 c to +125 c as2951cs-x -40 c to +125 c v in bottom view 13 2 v out gnd to-92 (n) pin connections alpha as2930 1 8-pin surface mount top view 2 3 4 5 6 7 8 as2951 output sense shutdown ground input feedback 5v or 3.3v tap error
rev. 9/29/00 as2950/as2951 absolute maximum ratings power dissipation..........................................internally limited input supply voltage (survival) .................. .......-20 to +60v lead temp. (soldering, 5 seconds) ................................ 260c feedback input voltage .................................. ...-1.5 to +30v storage temperature range ......................... -65c to +150c shutdown input voltage..................................... -0.3 to +30v operating junction temperature range error comparator output .................... ...............-0.3 to +30v as2951 .................................................. -55c to +150c esd rating ............................................ ................. 2kv min as2950ac/as2950c as2951ac/as2951c............................ -40c to +125c electrical characteristics at v s =15v, t a =25c, unless otherwise specified. parameter conditions as2951 as2950c/as2951c as2950c/as2951c units min typ max min typ max min typ max 3.0v version output voltage t j = 25 c -25 c < t j < 85 c full operating temperature 2.985 2.964 3.0 3.015 3.036 2.985 2.970 2.964 3.0 3.0 3.0 3.015 3.030 3.036 2.970 2.955 2.940 3.0 3.0 3.0 3.030 3.045 3.060 v output voltage 100ma < i l < 150ma t j < t jmax 2.955 3.0 3.045 2.958 3.0 3.042 2.928 3.0 3.072 v 3.3v version output voltage t j = 25 c -25 c < t j < 85 c full operating temperature 3.284 3.260 3.3 3.317 3.340 3.284 3.267 3.260 3.3 3.3 3.3 3.317 3.333 3.340 3.267 3.251 3.234 3.3 3.3 3.3 3.333 3.350 3.366 v output voltage 100ma < i l < 150ma t j < t jmax 3.251 3.3 3.350 3.254 3.3 3.346 3.221 3.3 3.379 v 5.0v version output voltage t j = 25 c -25 c < t j < 85 c full operating temperature 4.975 4.94 5.0 5.025 5.06 4.975 4.95 4.94 5.0 5.0 5.0 5.025 5.050 5.06 4.95 4.925 4.90 5.0 5.0 5.0 5.05 5.075 5.10 v output voltage 100 a < i l < 150ma t j < t jmax 4.925 5.0 5.075 4.93 5.0 5.07 4.88 5.0 5.12 v all voltage options output voltage temperature coefficient (note 1) 20 120 20 50 ppm/ c line regulation (note 3) 6v < v in < 30v (note 4) 0.03 0.1 0.03 0.1 0.04 0.2 % load regulation (note 3) 100ma < i l < 150ma 0.04 0.1 0.04 0.1 0.1 0.2 % i l = 100 a i l = 100ma dropout voltage (note 5) i l = 150ma 50 380 450 80 450 500 50 380 450 80 450 500 50 380 450 80 450 500 mv i l = 100 a i l = 100ma ground current i l = 150ma 150 3 5 170 6 8 150 3 5 170 6 8 150 3 5 170 6 8 a ma ma current limit v out = 0 130 200 130 200 130 200 ma thermal regulation 0.05 0.2 0.05 0.2 0.05 0.2 %/w output noise, 10hz to 100khz c l = 1 f c l = 200 f c l = 13.3 f (bypass = 0.01 f pins 6 to 1 (as2951)) 430 160 100 430 160 100 430 160 100 vrms vrms vrms 8-pin version only as2951 as2951ac as2951c reference voltage 1.22 1.235 1.25 1.22 1.235 1.25 1.21 1.23 1.26 v reference voltage o ver temperature (note 6) 1.19 1.27 1.19 1.27 1.18 1.28 v
rev. 9/29/00 feedback input output unregulated dc shutdown ground error ______ 5v tap sense 5v @ 150ma max to cmos or ttl reference error detection comparator error amplifier 1.23v from cmos or ttl + + + + + + 60 mv 3 7 8 1 2 6 5 4 ? .. 60k 330k 180k ? .. ? .. .. 1f _ _ as2950 and a2951 block diagram as2950/as2951 parameter conditions (note 2) as2951 min typ max as2950ac as2951ac min typ max as2950c as2951c min typ max units 8-pin version only (continued) feedback pin bias current 40 60 40 60 40 60 na reference voltage temperature coefficient ( note 7 ) 20 20 50 ppm/ c feedback pin bias current temperature coefficient 0.1 0.1 0.1 na/c error comparator output leakage current v oh = 30v 0.01 1 0.01 1 0.0 1 1 a output low voltage v in = 4.5v i ol = 400 a 150 250 150 250 150 250 mv upper threshold voltage (note 8) 40 60 40 60 40 60 mv lower threshold voltage (note 8) 75 95 75 95 75 95 mv hysteresis (note 8) 15 15 15 mv shutdown input input logic voltage low (regulator on) high (regulator off) 2 1.3 0.6 2 1.3 0.7 2 1.3 0.7 v v shut down pin input current v s = 2.4v v s = 30v 30 675 50 800 30 675 50 800 30 675 50 800 a a regulator output current in shutdown (note 9) 3 10 3 10 3 10 a note 1: output or reference voltage temperature coefficients defined as the worst case voltage change divided by the total temperature range. note 2: unless otherwise specified all limits guaranteed for t j = 25 c, v in = 6v, i l = 100 a and c l = 1 f. additional conditions for the 8-pin versions are feedback tied to 5v tap and output tied to output sense (v out = 5v) and v shutdown 0.8v. note 3: regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. changes in output voltag e due to heating effects are covered under the specification for thermal regulation. note 4: line regulation for the as2951 is tested at 150 c for i l = 1 ma. for i l = 100 a and t j = 125 c, line regulation is guaranteed by design to 0.2%. see typical performance characteristics for line regulation versus temperature and load current. note 5: dropout voltage is defined as the input to output differential at which the output voltage drops 100 mv below its nominal val ue measured at 1v differential at very low values of programmed output voltage, the minimum input supply voltage of 2v ( 2.3v over temperature) must be taken int o account. note 6: v ref v out (v in - 1v), 2.3 v in 30v, 100 a i l 150 ma, t j t jmax . note 7: output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperatu re range. note 8: comparator thresholds are expressed in terms of a voltage differential at the feedback terminal below the nominal reference vo ltage measured at 6v input. to express these thresholds in terms of output voltage change, multiply by the error amplifier gain = v out /v ref = (r 1 + r 2 )/r 2 . for example, at a programmed output voltage of 5v, the error output is guaranteed to go low when the output drops by 95 mv x 5v/1.235 = 384 mv. thresholds remain constant as a percent of v out as v out is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed. note 9: v shutdown 2v, v in 30v, v out =0, feedback pin tied to 5v tap. note 10: all typical values are not guaranteed. the value could vary from lot to lot. block diagram
rev. 9/29/00 as2950/as2951 application hints external capacitors the stability of the as2950/as2951 requires a 1.0 f or greater capacitor between output and ground. oscillation could occur without this capacitor. most types of tantalum or aluminum electrolytic works fine here. for operations below -25 c solid tantalum is recommended since many aluminum types have electrolytes that freeze at a bout -30 c. the esr of about 5 ? or less and resonant frequency above 500khz are the most important parameters in the value of the capacitor. the capacitor value can be increased without limit. at lower values of output current, less output capacitance is required for stability. for the currents below 10ma the value of the capacitor can be reduced to 0.5 f and 0.15 f for 1ma. more output capacitance is needed for the 8-pin version at voltages below 5v since it runs the error amplifier at lower gain. at worst case 5 f or greater must be used for the condition of 150ma load at 1.23v output. the as2950, unlike other low dropout regulators will remain stable in regulation with no load in addition to the internal voltage divider. this feature is especially important in applications like cmos ram keep-alive. when setting the output voltage of the as2951 version with external resistors, a minimum load of 1ua is recommended. if there is more than 10 inches of wire between the input and the ac filter capacitor or if a battery is used as the input then a 1 a tantalum or aluminum electrolytic capacitor should be pl aced from the input to the ground. instability can occur if there is stray capacitance to the as2951 feedback terminal (pin 7). this could cause more problems when using a higher value of external resistors to set the output voltage. this problem can be fixed by adding a 100pf capacitor between output and feedback and increasing the output capacitor to at least 3.3 f. error detection comparator output the comparator produces a logic low output whenever the as2951 output falls out of regulation by more than around 5%. this is around 60mv offset divided by the 1.235 reference voltage. this trip level remains 5% below normal regardless of the programmed output voltage of the regulator. figure 1 shows the timing diagram depicting the error signal and the regulator output voltage as the as2951 input is ramped up and down. the error signal becomes low at around 1.3v input, and goes high around 5v input (input voltage at which v out = 4.75 ). since the as2951?s dropout voltage is load dependent, the input voltage trip point (around 5v) will vary with the load current. the output voltage trip point (approx. 4.75v) does not vary with load. . the error comparator has an open-collector output which requires an external pull-up resistor. depending on the system requirements the resistor may be returned to 5v output or other supply voltage in determining the value of this resistor, note that the output is rated to sink 400 a, this value adds to battery drain in a low battery condition. suggested values range from 100k to 1m ? . if the output is unused this resistor is not required. programming the output voltage of as2951 the as2951 may be pin-strapped for 5v using its internal voltage divider by tying pin 1 (output) to pin 2 (sense) and pin 7 (feedback) to pin 6 (5v tap). also it may be programmed for any output voltage between its 1.235v reference and its 30v maximum rating . as seen in figure 2, an external pair of resistors is required. refer to the below equation for the programming of the output voltage. v out = v ref ( 1 + r 1 /r 2 )+ i fb r 1 the v ref is 1.235 and i fb is the feedback bias current, nominally -20 na. the minimum recommended load current of 1 a forces an upper limit of 1.2 m ? on value of r 2 . if no load presented the i fb produces an error of typically 2% in v out which may be eliminated at room temperature by trimming r 1 . to improve the accuracy choose the value of r 2 = 100k this reduces the error by 0.17% and increases the resistor program current by 12 a. since the as2951 typically draws 60 a at no load with pin 2 open-circuited this is a small price to pay. reducing output noise it may be an advantage to reduce the ac noise present at the output. one way is to reduce the regulator bandwidth by increasing the size of the output capacitor. this is the only way that noise can be reduced on the as2950 but is relatively inefficient, as increasing the capacitor from 1 f to 220 f only decreases the noise from 430 v to 160 v rms . for a 100khz bandwidth at 5v output. noise could also be reduced fourfold by a bypass capacitor across r 1 , since it reduces the high frequency gain from 4 to unity. pick c bypass ? 1 / 2 r 1 200 hz or choose 0.01 f. when doing this, the output capacitor must be increased to 3.3 f to maintain stability. these changes reduce the output noise from 430 v to 100 v rms . for a 100khz bandwidth at 5v output. with the bypass capacitor added, noise no longer scales with output voltage so that improvements are more dramatic at higher output voltages.
rev. 9/29/00 as2950/2951 typical performance characteristics input current (ma) 160 150 140 130 70 50 0 input voltage (volts) ground pin current (ma) 10 1 0.1 0.01 0.1 1 10 150 load current (ma) 120 110 100 90 80 60 40 30 20 10 0 1234 5 678910 input current quiescent current 240 220 200 180 -75 -50 -25 0 25 50 75 100 125 150 temperature (oc) quiescent current quiescent current (a) 170 150 130 110 -75 -50 -25 0 25 50 75 100 125 150 temperature (oc) short circuit current short circuit current (ma) 160 140 120 110 v in =6v i l =100ma r l =50 ? 600 400 300 50 -75 -50 -25 0 25 50 75 100 125 150 temperature (oc) drop-out voltage drop-out voltage (mv) 500 100 0 output voltage (v) 5.06 5.04 5.0 temperature (oc) output voltage (volts) 0 0 input voltage (volts) 5.02 4.98 4.96 4.94 output voltage vs. temp of 3 representative units dropout characteristics 16 12 8 4 -75 -50 -25 0 25 50 75 100 125 150 temperature (oc) ground current ground current (ma) 123 456 1 2 3 4 5 6 -75 -50 -25 0 25 50 75 100 125 150 0.2% i l = 100ma i l = 100a r l =50k ? r l =50k ? v in = 6v i l = 100ma ~ ~ input current (a) 75 0 0 10 150 input voltage (volts) input current ground current (a) 320 280 0 input voltage (volts) 240 80 40 0 1234 5 6 7 8 ground current 16 14 12 0 1 2345678 input voltage ground current ground current r l = 50k ? 25 50 100 125 150 175 200 225 250 123 120 160 200 10 8 6 4 2 0 i l = 1ma i l = 0 i l =100ma t j = 25oc drop-out voltage output current drop-out voltage (mv) 100ma 10ma 1ma 100a 500 400 300 200 100 0 r l = 8
rev. 9/29/00 as2950/as2951 typical performance characteristics (continued) 10 0.5 0.1 0.02 10 100 1k 10k 100k 1m frequency (hz) output impedance output impedance (ohms) 5 0.2 0.05 0.01 90 70 60 40 10 1 10 2 10 3 10 4 10 5 10 6 frequency (hz) ripple rejection ripple rejection (db) 80 50 20 ripple rejection frequency (hz) ripple rejection (db) 10 6 10 3 10 2 10 1 90 80 70 60 50 20 1 2 30 i l = 100a i l = 0 c l = 1f v in = 6v v out = 5v 40 30 10 4 10 5 i l = 10ma i l = 10ma c l = 1f v in = 6v v out = 5v i o = 100ma i o = 100a i o = 1ma v out = 5v c l = 1f comparator output (v) 8 6 0 input voltage (v) 4 2 0 -2 123 45 error comparator output sink current (ma) 2.5 1.5 output low voltage (v) 2.0 1.0 0.5 0.0 comparator sink current time(s) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 v out = 5v pullup resistor to separate 5v supply hysteresis 100 0 200 400 600 800 line transient response input output voltage voltage change 4v 6v 8v -50 0 50 ~ ~ mv mv mv c l = 1f i l = 1ma v out = 5v t a = -55oc t a = 25oc t a = 125oc as2951 7 6 4 -100 0 100 200 300 400 500 600 700 time enable transient shutdown output pinout voltage (v) voltage (v) 3 2 1 0 2 -2 250 100 -50 100 01 2345 time (ms) load transient response load output voltage current change (mv) a ~ ~ ma -100 0 50 150 200 c l = 1f v out = 5v 80 20 -40 100 04 8121620 time (ms) load transient response load output voltage current change (mv) a 100 -60 -20 0 40 60 a c l = 1f v out = 5v 0 5 c l = 10f v out = 5v v in = 8v i l = 10ma 100 ~ ~ minimum operating voltage (v) 10 1 0.1 0.01 -75 0 75 150 temperature minimum operating voltage bias current (na) -30 -75 tempeature (oc) feedback bias current feedback current (a) -150 -250 -2.0 -0.5 1.0 feedback voltage (v) feedback pin current -50 0 50 75 100 150 -20 -10 0 10 20 -200 -100 -50 0 50 -1.5 -1.0 -50 -25 25 50 100 125 -25 25 125 0 0.5 t a = 25oc t a = 55oc t a =1 25oc as2951 as2951 as2951 pin 7 driven by external source (regulator run open loop)
rev. 9/29/00 as2950/as2951 typical performance characteristics (continued) voltage noise spectral density (v/hz) 3.5 2.5 2.0 0.0 10 2 10 3 10 4 10 5 frequency (hz) output noise i l = 100ma c l = 1f c l = 220f c l = 3.3f 3.0 1.5 1.0 0.5 output current (ma) 120 100 60 40 0 input voltage (v) 80 20 0 510 15 202530 as2950 maxium rated output current t jmax = 125o c v out = 5v t a = 25oc t a = 50oc t a = 85oc 8-pin molded dip soldered to pc board shutdown threshold voltage (v) 1.8 1.6 1.0 -75 temperature (oc) 1.4 1.2 0.8 0.6 -50 -25 0 25 50 75 100 125 150 shutdown threshold voltage output current (ma) 120 80 0 010 20 30 input voltage (v) as2950 maxium rated output 25 15 5 t a = 85 oc t a =25 oc t jmax = 125 oc 0.25" leads soldered to-92 package to pc board 100 60 40 20 ripple rejection (db) 80 60 40 10 10 1 10 3 10 4 10 6 frequency (hz) ripple rejection i l = 50a i l = 100ma c l = 1f v in = 6v v out = 5v 70 50 30 20 10 2 10 5 output voltage change (mv) 30 25 20 10 5 input voltage (v) 15 10 5 0 5 0 -5 -10 10 15 20 25 30 line regulation ~ ~ i l = 100a i l = 1ma t j = 150 oc t j = 125 oc i l = 100a pin 2 to pin 4 resistance (k ?) ?) ?) ?) 400 200 100 0 -75 0 75 150 temperature (oc) as2951 divider resistance -50 -25 25 50 100 125 300 power output voltage dissipation (w) change (mv) 4 2 1 0 time (s) 0 -2 0 -1 10 20 30 40 50 thermal response 5 1.25w ~ ~
rev. 9/29/00 as2950/as2951 typical applications + + + + 4.75v output voltage error* _______ input voltage 1.3v 5.0v figure 1. error output timing _______ * see application info. 100k output error error ______ sd v out gnd fb +v in +v in 1.23v 1.2 to 30v r 1 .01uf 3.3uf r 2 v ref 3 8 5 1 4 7 shutdown input + figure 2. adjustable regulator as2951 470k error ______ sd v out gnd +v in +v in r 1 1uf r 2 3 8 5 1 4 + fb 7 v out ? .. ? .. 470k alpha 2951 latch off when error flag occurs output error error ______ sd v out gnd fb +v in +v in *v out = v in 3 8 5 1 4 7 shutdown input alpha 2951 wide input vltage range current limiter *minimum input-output voltage ranges from 4mv to 400mv. depending on load current. current limit is typically 160ma
rev. 9/29/00 as2950/as2951 typical applications (continued) 100k sense sd v out gnd +v in 3 8 1 1uf + 4 ? .. ? .. 400k 120k 1.5k ? .. ? .. 6v sealed lead- acid battery source fb for 5.5 v + 1n457 2 ? .. 20k ni-cad backup battery memory v+ main v- as385 low battery disconnect alpha 2951 gnd 4 3 5 8 2 1 7 6 sd tap fb +v in sense v out error reset 100k ? ? ? ? 100k ? ? ? ? 100k ? ? ? ? 1k ? ? ? ? 100k ? ? ? ? 10k ? ? ? ? 20k ? ? ? ? 1k ? ? ? ? 39k ? ? ? ? 39k ? ? ? ? c3 c1 c2 c4 1% 1% 1% 1% 6v lead- acid battery r 3 <6.2v** <5.8v** <6.0v** - + + + + - - - +v out = 5v 1 f + regulator with state-of-charge indicator 2951 *optional latch off when dropout occurs. adjust r3 for c2 switching v in is 6.0v. **outputs go low when v in drops below designated thresholds.
rev. 9/29/00 as2950/as2951 typical applications (continued) 100k sense sd v out gnd +v in 3 8 1 1uf + 4 ? ? ? ? .. ? ? ? ? .. 400k 120k 1.5k ? ? ? ? .. ? ? ? ? .. 6v sealed lead- acid battery source fb for 5.5 v + 1n457 2 ? ? ? ? .. 20k ni-cad backup battery memory v+ main v- as385 low battery disconnect 2951 gnd 4 3 5 8 2 1 7 6 sd tap fb +v in sense v out error ______ reset 100k 100k 100k 1k 100k 10k 20k 1k 39k 39k c3 c1 c2 c4 1% 1% 1% 1% 6v lead- acid battery r 3 <6.2v** <5.8v** <6.0v** - + + + + - - - ? ? ? ? .. ? ? ? ? .. ? ? ? ? .. ? ? ? ? .. ? ? ? ? .. ? ? ? ? .. ? ? ? ? .. ? ? ? ? .. ? ? ? ? .. ? ? ? ? .. +v out = 5v 1uf + regulator with state-of-charge indicator 2951 *optional latch off when dropout occurs. adjust r3 for c2 switching v in is 6.0v. **outputs go low when v in drops below designated thresholds.
rev. 9/29/00 as2950/as2951 typical applications (continued) 330k in v out fb 3 5 1 4.7uf + 7 ? ? ? ? .. ? ? ? ? .. 27k 2951 v tap gnd sense 4 2 unregulated input 2n5432 5v output load 50ma to 300 ma 300 ma regulator with 0.75 dropout 360k 0.1uf v out min voltage = 4v +v in 8 1 fb 7 1n4001 20ma 1n457 4.7ma +5v output 2 gnd 4 4 open circuit detector for 4ma to 20ma current loop 2951 ? ? ? ? .. external circuit protected from over temperature (v+ goes off when temp > 125) or relay 8.2k temp sensor gnd v out fb sd +v in +v in 10k 5 degree shutdown flag error _______ 3 5 8 4 7 1 aux shutdow input off on ? ? ? ? .. as35 + - system over temperature protection circuit 2951 ? ? ? ? ..
rev. 9/29/00 as2950/as2951 schematic diagram

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