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mic2940a/2941a 1.2a low-dropout voltage regulator micrel inc. 2180 fortune drive san jose, ca 95131 usa tel +1 ( 408 ) 944-0800 fax + 1 (408) 474-1000 http://www.micrel.com july 2007 m9999-071307 general description the mic2940a and mic2941a ar e bulletproof efficient voltage regulators with very low dropout voltage (typically 40mv at light loads and 350mv at 1a), and low quiescent current (240a typical). the quiescent current of the mic2940a increases only slightly in dropout, thus prolonging battery life. key mic2940a features include protection against reversed battery, fold-back current limiting, and automotive l oad dump protection (60v positive transient). the mic2940 is available in both ? xed voltage (3.3v, 5v, and 12v) and adjustable voltage con ? gurations. the mic2940a-xx devices are three pin, ? xed voltage regulators. a logic-compatible shutdown input is provided on the adjustable mic2941a, which enables the regulator to be switched on and off. data sheets and support doc umentation can be found on micrels web site at: www.micrel.com. features ? high output voltage accuracy ? guaranteed 1.25a output ? low quiescent current ? low dropout voltage ? extremely tight load and line regulation ? very low temperature coef ? cient ? current and thermal limiting ? input can withstand C20v reverse battery and +60v positive transients ? logic-controlled electronic shutdown ? output programmable from 1.24v to 26v(mic2941a) ? available in to-220, to-263, to-220-5, and to-263-5 packages. applications ? battery powered equipment ? cellular telephones ? laptop, notebook, and palmtop computers ? pcmcia vcc and vpp regulation/switching ? bar code scanners ? automotive electronics ? smps post-regulator/ dc-to-dc modules ? voltage reference ? high efficiency linear power supplies ___________________________________________________________________________________________________________ pin configuration 123 1234 5 12 3 to-263-3 (mic2940a-xxbu/wu) mic2940a pinout 1) input 2) ground 3) output 12345 to-263-5 (mic2941abu/wu) mic2941a pinout 1) adjust 2) shutdown 3) ground 4) input 5) output to-220-3 (mic2940a-xxbt/wt) the tab is ground on to-220 and to-263 packages to-220-5 (mic2941abt/wt) downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 2 m9999-071307 ordering information part number voltage temperature range package lead finish mic2940a-3.3bt 3.3v C40 to +125c 3-pin to-220 standard mic2940a-3.3bu 3.3v C40 to +125c 3-pin to-263 standard mic2940a-3.3wt 3.3v C40 to +125c 3-pin to-220 rohs comliant (1) mic2940a-3.3wu 3.3v C40 to +125c 3-pin to-263 rohs comliant (1) mic2940a-5.0bt 5v C40 to +125c 3-pin to-220 standard mic2940a-5.0bu 5v C40 to +125c 3-pin to-263 standard mic2940a-5.0wt 5v C40 to +125c 3-pin to-220 rohs comliant (1) mic2940a-5.0wu 5v C40 to +125c 3-pin to-263 rohs comliant (1) mic2940a-12bt 12v C40 to +125c 3-pin to-220 standard mic2940a-12bu 12v C40 to +125c 3-pin to-263 standard mic2940a-12wt 12v C40 to +125c 3-pin to-220 rohs comliant (1) mic2940a-12wu 12v C40 to +125c 3-pin to-263 rohs comliant (1) mic2941abt adj. C40 to +125c 5-pin to-220 standard mic2941abu adj. C40 to +125c 5-pin to-263 standard mic2941awt adj. C40 to +125c 5-pin to-220 rohs comliant (1) MIC2941AWU adj. C40 to +125c 5-pin to-263 rohs comliant (1) note: 1. rohs compliant with hot-melting solder exemption. schematic diagram downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 3 m9999-071307 absolute maximum ratings if military/aerospace speci ? ed devices are required, contact your local micrel representative/distributor for availability and speci ? cations power dissipation (note 1 ) .......................interna lly limited lead temperature (solde ring, 5 se c.)........................ 260c storage temperature ................................C65c to +150c operating junction temper ature ..............C40c to +125c to-220 ( jc ) ........................................................2c/w to-263 ( jc ) ........................................................2c/w input supply voltage ...................................... C20v to +60v operating input supply vo ltage .......................... 2v ? to 26v adjust input voltage ( notes 9 and 10 ) ......... C1.5v to +26v shutdown input volt age ................................ C0.3v to +30v error comparator output voltage ................. C0.3v to +30v ? across the full operating temperature, the minimum input voltage range for full output current is 4.3v to 26v. output will remain in-regulation at lower output voltages and low current loads down to an input of 2v at 25c. electrical characteristics limits in standard typeface are for t j = 25c and limits in boldface apply over the full operating temperature range. unless otherwise speci ? ed, v in = v out + 1v, i l = 1000ma, c l = 10f. the mic2941a is programmed to output 5v and has v shutdown 0.6v. symbol parameter condition min typ max units v o output voltage accuracy 5 ma i l 1a C1 C2 C2.5 1 2 2.5 % % % ? v o ? t output voltage temperature coefficient (note 2) 20 100 ppm/c line regulation i o = 10ma, (v out + 1v) v in 26v 0.06 0.50 % ? v o v o load regulation i l = 5ma to 1.25a i l = 5ma to 1a ( note 3 ) 0.04 0.16 0.20 % % v in C v o dropout voltage ( note 4) i l = 5ma i l = 250ma i l = 1000ma i l = 1250ma 60 200 350 400 150 180 250 320 450 600 600 mv mv mv mv mv mv mv i gnd ground pin current ( note 5 ) i l = 5ma i l = 250ma i l = 1000ma i l = 1250ma 240 3 22 35 500 4.5 6 35 45 70 a ma ma ma ma ma i gnddo ground pin current at dropout ( note 5 ) v in = 0.5v less than designed v out (v out 3.3) i l = 5ma 330 600 a i limit current limit v out = 0v ( note 6 ) 1.6 3.5 a ? v o ? p d thermal regulation ( note 7 ) 0.05 0.2 %/w e n output noise voltage (10hz to 100khz) i l = 100ma c l = 10f c l = 33f 400 260 v rms v rms downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 4 m9999-071307 electrical characteristics (mic2941a only) parameter condition min typ max units reference voltage ( note 8 ) 1.223 1.210 1.204 1.235 1.2471.260 1.266 v v v adjust pin bias current 20 40 60 na na reference voltage temperature coefficient 20 ppm/c adjust pin bias current temperature coefficient 0.1 na/c shutdown input input logic voltage low (on) high (off) 2.0 1.3 0.7 v v v v shutdown = 2.4v 30 50 100 a a shutdown pin input current v shutdown = 26v 450 600 750 a a regulator output current in shutdown ( note 10 ) 3 30 60 a a notes: 1. absolute maximum ratings indicate limits beyond wh ich damage to the component may occur. electrical speci ? cations do not apply when operating the device outside of its rated operating conditions. the maximum allowable power dissipation is a function of the maxi mum junction temperature, t j(max) , the junction-to-ambient thermal resistance, ja , and the ambient temperature, t a . the maximum allowable power dissipation at any ambient temperature is calculated using: p (max) = (t j(max) C t a ) / ja . exceeding the maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. 2. output voltage temperature coef ? cient is de ? ned as the worst case voltage change divided by the total temperature range. 3. regulation is measured at constant junction temperature using low duty cycle pulse testing. changes in output voltage due to heating effects are covered by the thermal regulation speci ? cation. 4. dropout voltage is de ? ned as the input to output differential at which the output voltage drops 100 mv below its nominal value measured at 1v differential. at low values of programmed output voltage, the minimum input supply voltage of 4.3v over temperature mus t be taken into account. 5. ground pin current is the regulator quiescent current. the total current drawn from the source is the sum of the load cu rrent plus the ground pin current. 6. the mic2940a features fold-ba ck current limiting. the short circuit (v out = 0v) current limit is less than the maximum current with normal output voltage. 7. thermal regulation is de ? ned as the change in output voltage at a time t after a c hange in power dissipation is applied, excluding load or line regulation effects. speci ? cations are for a 200ma load pulse at v in = 20v (a 4w pulse) for t = 10ms. 8. v ref v out (v in C 1 v), 4.3v v in 26v, 5ma < i l 1.25a, t j t j(max) . 9. circuit of figure 3 with r1 150k ? . v shutdown 2 v and v in 26 v,v out = 0. 10. when used in dual supply systems where the regulator load is returned to a negat ive supply, the output voltage must be dio de clamped to ground. 11. maximum positive supply voltage of 60 v must be of limited duration (< 100 ms) and duty cycle ( 1%). the maximum continuous supply voltage is 26v. downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 5 m9999-071307 typical characteristics 0 100 200 300 400 500 0.00 0.25 0.50 0.75 1.00 1.25 dropout voltage (mv) output current (a) dropout voltage vs. output current 0 200 400 600 800 1000 -60 -30 0 30 60 90 120 150 dropout voltage (mv) temperature (c) dropout voltage vs. temperature i load = 1.25a 0 1 2 3 4 5 6 0123456 output voltage (v) input voltage (v) dropout characteristics i load =5ma i load = 1.25a 0.1 1 10 40 11 0 100 1000 10000 ground current (ma) output current (ma) ground current vs. output current 10a 0 100 200 300 400 01234567 8 ground current (a) supply voltage (v) ground current vs. supply voltage fixed 5v i load =5ma 0 10 20 30 40 50 024681 0 ground current (ma) input voltage (v) ground current vs. supply voltage fixed 3.3v device i load =1.25a 0.00 0.10 0.20 0.30 0.40 -60 -30 0 30 60 90 120 150 ground current (ma) temperature (c) ground current vs. temperature i load =5ma 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -60 -30 0 30 60 90 120 150 ground current (ma) temperature (c) ground current vs. temperature i load =100ma 0 10 20 30 40 50 -60 -30 0 30 60 90 120 150 ground current (ma) temperature (c) ground current vs. temperature i load =1.25a i load = 100ma 3.20 3.22 3.24 3.26 3.28 3.30 3.32 3.34 3.36 3.38 3.40 -60 -30 0 30 60 90 120 150 output voltage (v) temperature (c) fixed 3.3v output voltage vs. temperature 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -60 -30 0 30 60 90 120 150 current (a) temperature (c) short circuit and maximum current vs. temperature v out =v nominal C0.5v v out =0v fixed 3.3v version 3samples -200 0 200 400 600 800 1000 -30 -20 -10 0 10 20 30 ground current (a) input voltage (v) ground current vs. input voltage r load = 100 downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 6 m9999-071307 typical characteristics (continued) 0 25 50 75 100 125 -60 -30 0 30 60 90 120 150 enable current (a) temperature (c) mic29401/2 shutdown current vs. temperature v en =5v v en =2v -500 -250 0 250 500 750 output (mv) -0.5 0.0 0.5 1.0 1.5 2.0 -5 051 0 output (a) time (ms) load transient c out =10f 5ma -200 -100 0 100 200 output (mv) -0.5 0.0 0.5 1.0 1.5 2.0 -5 051 0 output (a) time (ms) load transient c out = 100 f 5ma 0 10 20 30 40 50 -60 -30 0 30 60 90 120 150 adjust pin current (na) temperature (c) mic29402/3 adjust pin current vs. temperature i load =5ma -40 -20 0 20 40 output (mv) 4 6 8 10 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 input (v) time (ms) line transient c out =10f -10 0 10 20 output (mv) 4 6 8 10 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 input (v) time (ms) line transient c out = 100 f 0.01 0.1 1 10 1x10 0 10x10 0 100x10 0 1x10 3 10x10 3 100x10 3 1x10 6 output impedance ( ) frequency (hz) output impedance vs. frequency i load = 10ma downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 7 m9999-071307 application information external capacitors a 10f (or greater) capacitor is required between the mic2940a output and ground to prevent oscillations due to instability. most types of tantalum or aluminum electrolytics will be adequate; ? lm types will work, but are costly and therefore not recommended. many aluminum electrolytics have el ectrolytes that freeze at about C30c, so solid tantalums are recommended for operation below C25c. the important parameters of the capacitor are an effective series resistance of about 5 ? or less and a resonant frequency above 500khz. the value of this capacitor may be increased without limit. at lower values of output current, less output capacitance is required for output stability. the capacitor can be reduced to 3.3f for current below 100ma or 2.2f for currents below 10ma . adjusting the mic2941a to voltages below 5v runs the error ampli ? er at lower gains so that more output capacitance is needed. for the worst-case situation of a 1.25a load at 1.23v output (output shorted to adjust) a 22f (or greater) capacitor should be used. the mic2940a will remain st able and in regulation with load currents ranging from 5ma on up to the full 1.25a rating. the external resistors of the mic2941a version may be scaled to draw th is minimum load current. a 0.22f capacitor should be placed from the mic2940a input to ground if there is more than 10 inches of wire between the input and the ac ? lter capacitor or if a battery is used as the input. programming the output voltage (mic2941a) the mic2941a may be programmed for any output voltage between its 1.235v reference and its 26v maximum rating. an external pai r of resistors is required, as shown in figure 3. v out = v ref x { 1 + r 1 /r 2 } C |i fb | r 1 where v ref is the nominal 1.235 reference voltage and i fb is the adjust pin bias current, nominally 20na. the minimum recommended load current of 1a forces an upper limit of 1.2m ? on the value of r 2 , if the regulator must work with no load (a condition often found in cmos in standby), i fb will produce a C2% typical error in v out which may be eliminated at room temperature by trimming r 1 . for better accuracy, choosing r 2 = 100k ? reduces this error to 0.17% while increasing the resistor program current to 12a. since the mic2941a typically draws 100a at no load with shutdown open- circuited, this is a negligible addition. reducing output noise in reference applications it may be advantageous to reduce the ac noise present at the output. one method is to reduce the regulator bandwidth by increasing the size of the output capacito r. this is relatively inef ? cient, as increasing the capacitor from 1f to 220f only decreases the noise from 430v to 160v rms for a 100khz bandwidth at 5v output. noise can be reduced by a factor of four with the mic2941a by adding a bypass capacitor across r 1 . pick 200hz r 2 1 c 1 bypass ? or about 0.01f. when doing this, the output capacitor must be increased to 22f to maintain stability. these changes reduce the output noise from 430v to 100v rms for a 100khz bandwidth at 5v output. with the bypass capacitor added, noise no longer scales with output voltage so that improv ements are more dramatic at higher output voltages. automotive applications the mic2940a is ideally suited for automotive applications for a variety of reasons. it will operate over a wide range of input voltages with very low dropout voltages (40mv at light load s), and very low quiescent currents (240a typical). these features are necessary for use in battery powered systems, such as automobiles. it is a bulletpr oof device with the ability to survive both reverse battery (negative transients up to 20v below ground), and load dump (positive transients up to 60v) conditions. a wide operating temperature range with low temperature coef ? cients is yet another reason to use these versatile regulators in automotive designs. not * valid not * valid output voltage 4.75v error input voltage 5v 1.3v figure 1. error output timing downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 8 m9999-071307 typical applications v in +v in v out v out = 5v gnd 10f + figure 2. mic2940a-5.0 fixed +5v regulator out gnd adjust v v in +v in v out =v in * minimum input-output voltage ranges from 40mv to 400mv, depending on load current. figure 4. mic2941a wide input voltage range current limit in out gnd adjust shutdown v v shutdown input in +v out v 1.2v 26v 1 r 100pf 22f 2 r 1.23v ref v v out =v ref x (1 + ) 1 r 2 r off on figure 3. mic2941a adjustable regulator shutdown v gnd out +v in adj shutdowninput 100pf 2n2222 1% 300k +5v to +7v 1% 180k + 10f 470 k off on 5v 3.3v 220k 1% v cc out adjust pin low = enable output. q1 on = 3.3v, q1 off = 5.0v. figure 5. mic2941a 5.0v or 3.3v selectable regulator with shutdown downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 9 m9999-071307 package information 3-pin to-220 (t) 3-pin to-263 (u) downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 10 m9999-071307 5-pin to-220 (t) 5-pin to-263 (u) downloaded from: http:///
micrel, inc. mic2940a/2941a july 2007 11 m9999-071307 micrel, inc. 2180 fortune drive san jose, ca 95131 usa tel +1 (408) 944-0800 fax +1 (408) 474-1000 web http://www.micrel.com the information furnished by micrel in this data sheet is belie ved to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change circuitry and specifications at any time without notification to the customer. micrel products are not designed or authori zed for use as components in life support appliances, devices or systems where malfu nction of a product can reasonably be expected to result in personal injury. life suppo rt devices or systems are devices or systems that (a) are in tended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significan t injury to the user. a purchasers use or sale of micrel produc ts for use in life support app liances, devices or systems is a purchasers own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2004 micrel, incorporated. downloaded from: http:///

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