mic37252 2.5a, low voltage cap ldo regulator superswitcher and super ?eta pnp are trademarks of micrel, inc. micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 ( 408 ) 944-0800 ? fax + 1 (408) 474-1000 ? http://www.micrel.com february 2006 m9999-021606 (408) 955-1690 general description the micrel mic37252 is a 2.5a low-dropout linear voltage regulator that provides a lo w voltage, high current output with a minimum of external components. it offers high precision, low dropout and low ground current. the mic37252 operates from an input voltage of 3.0v to6.0v. it is designed to drive digital circuits requiring low voltage at high currents (i.e., pl ds, dsp, microcontroller, etc.). it is available in an ad justable output voltage capable of 1.24v to 5.5v. features of the mic37252 ldo include thermal and current limit protection, and reverse current and reverse battery protection. junction temperature range of the mic37252 is from ?40c to +125c. for higher currents see the mic3730x family of ldos. features ? 2.5a minimum guarant eed output current ? ideal for 3.3v to 1.8v conversion ? stable with ceramic or tantalum capacitor ? 2.0% initial output tolerance ? dropout voltage = 550mv @ 2.5a ? excellent line and load regulation specifications ? logic controlled shutdown ? thermal shutdown and current limit protection ? reverse-leakage protection ? s-pak and to-263 packages applications ? ldo linear regulator for low-voltage digital ic ? pc add-in cards ? high efficiency linear power supplies ? smps post regulator ? battery charger ____________________________________________________________________________________________________________ typical application adjustable regulator
micrel, inc. mic37252 february 2006 2 m9999-021606 (408) 955-1690 ordering information part number standard rohs compliant** output current voltage* junction temperature range package mic37252br MIC37252WR 2.5a a dj. ?40 to +125c s-pak-5 mic37252bu mic37252wu 2.5a adj. ?40 to +125c to-263-5 *for other voltages, please contact micrel marketing. **rohs compliant with ?high melting solder? exemption. pin configuration s-pak5 (r) to-263 (u) pin description pin number pin name pin function 1 en enable (input): cmos compatible input. logic high = enable, logic low = shutdown. 2 vin input voltage which supplies cu rrent to the output power device. 3 gnd ground (tab is connected to ground on s-pak). 4 vout regulator output. 5 adj adjustable regulator feedback inpu t. connect to resistor voltage divider.
micrel, inc. mic37252 february 2006 3 m9999-021606 (408) 955-1690 absolute maximum ratings (1) supply voltage (v in ) ......................................................6.5v enable input voltage (v en )............................................6.5v power dissipation .....................................in ternally limited junction temper ature .........................?40c t j +125c storage temper ature ..........................?65c t j +150c lead temperature (solde ring, 5sec .) ......................... 260c eds (3) operating ratings (2) supply voltage (v in ) ......................................... 3.0v to 6.0v enable input voltage (v en ).................................. 0v to 6.0v junction temperat ure rang e .............?40c t j +125c maximum power dissipation (4) package thermal resistance s-pak ( jc ) ..........................................................2c/w to-263-5 ( jc ).....................................................2c/w electrical characteristics (5) t a = 25c with v in = v out + 1v; v en = v in ; i l = 10ma, bold values indicate ?40c< t j < +125c, unless otherwise noted. parameter condition min typ max units i l = 10ma -2 +2 % output voltage accuracy 10ma < i out < i l(max) , v out + 1 v in 6v -3 +3 % output voltage line regulation v in = v out + 1.0v to 6.0v, i l = 10ma 0.02 0.5 % output voltage load regulation i l = 10ma to 2.5a 0.2 1 % i l = 1.5a 400 500 mv v in ? v out ; dropout voltage, note 6 i l = 2.5a 550 1000 mv ground pin current, note 7 i l = 2.5a 40 60 ma ground pin current in shutdown v il 0.5v, v in = v out + 1v 1.0 a current limit v out = 0; v in = 3.3v 3 a start-up time v en = v in , i out = 10ma, c out = 47f 150 250 s enable input regulator enable 2.25 v enable input threshold regulator shutdown 0.8 v v il 0.8v (regulator shutdown) 2 4 a a enable pin input current v ih 2.25v (regulator enable) 1 10 30 a reference voltage 1.215 1.202 1.240 1.265 1.277 v v adjust pin bias current 40 80 120 na na notes: 1. exceeding the absolute maximum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. device is esd sensitive. handling precautions recommended. 4. p d(max) = t j(max) ? t a ) / ja , where ja , depends upon the printed circuit layou t. see ?applications information.? 5. specification for packaged product only 6. v do = v in ? v out when v out decreased to 98% of its nominal output voltage with v in = v out + 1v. for output voltages below 2v, dropout voltage specification does not apply due to a minimum input operating voltage of 3v 7. i gnd is the quiescent current. i in = i gnd + i out .
micrel, inc. mic37252 february 2006 4 m9999-021606 (408) 955-1690 typical characteristics 0 10 20 30 40 50 60 70 ) b d ( s s r p frequency (hz) psrr 100ma 1a 2.5a 10 1 100 1k 10k 100k 1m c out = 100f ceramic v in = 3.3v v out = 1.8v 0 10 20 30 40 50 60 70 ) b d ( r r s p frequency (hz) psrr 100ma 2.5a 1a 1 10 100 1k 10k 100k 1m c out = 47f v in = 3.3v v out = 1.8v 0 100 200 300 400 500 600 00.511.522.5 ) v m ( e g a t l o v t u o p o r d output current (a) dropout voltage v out = 3.3v 0 100 200 300 400 500 600 -40 -20 0 20 40 60 80 100 120 ) v m ( e g a t l o v t u o p o r d temperature ( c) dropout vs. temperature 3.3v out 2.5a load 1.75 1.76 1.77 1.78 1.79 1.80 1.81 1.82 1.83 1.84 1.85 -40 -20 0 20 40 60 80 100 120 ) v ( e g a t l o v t u p t u o temperature ( c) output voltage vs. temperature 0 2 4 6 8 10 12 14 16 18 -40 -20 0 20 40 60 80 100 120 ( t n e r r u c e l b a n e) a temperature ( c) enable pin current vs. temperature 100ma load 0 0.5 1 1.5 2 2.5 3 3.5 4 -40 -20 0 20 40 60 80 100 120 ) a ( t n e r r u c t i u c r i c t r o h s temperature t j (c) short circuit current vs. temperature v out = 0v v in = 4.3v 0 5 10 15 20 25 30 35 40 45 50 012345 ) a m ( t n e r r u c d n u o r g supply voltage (v) ground current vs. supply voltage 0.5a 1.5a 2.5a 0 5 10 15 20 25 30 35 40 45 50 -40 -20 0 20 40 60 80 100 120 ) a m ( t n e r r u c d n u o r g temperature ( c) ground current vs. temperature 1a load 10ma load 2.5a load 0 5 10 15 20 25 30 35 40 45 50 00.511.522.5 ) a m ( t n e r r u c d n u o r g output current (a) ground current vs. output current 2.490 2.492 2.494 2.496 2.498 2.500 2.502 2.504 2.506 2.508 2.510 00.511.522.5 ) v ( e g a t l o v t u p t u o output current (a) output voltage vs. load current 2.5v out 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 01234 ) v ( e g a t l o v t u p t u o supply voltage (v) dropout characteristics 0.5a 1.5a 2.5a
micrel, inc. mic37252 february 2006 5 m9999-021606 (408) 955-1690 functional characteristics time (400s/div.) t n e r r u c t u p t u o ) . v i d / a 1 ( e g a t l o v t u p t u o ) . v i d / v m 0 0 1 ( v in = 3.3v v out = 1.8v c out = 47f loadtransient response 10ma 2a time (400s/div.) t n e r r u c t u p t u o ) . v i d / a 1 ( e g a t l o v t u p t u o ) . v i d / v m 0 0 2 ( v in = 3.3v v out = 1.8v c out = 47f loadtransient response 10ma 2.5a line transient response time (100s/div.) e g a t l o v t u p t u o ) . v i d / v m 0 2 ( e g a t l o v t u p n i ) . v i d / v 2 ( 5v 3.3v
micrel, inc. mic37252 february 2006 6 m9999-021606 (408) 955-1690 application information the mic37252 is a high-performance low-dropout voltage regulator suitable for moderate to high-current regulator applications. its 550mv dropout voltage at full load makes it especially valuable in battery-powered systems and as high-efficien cy noise filters in post- regulator applications. unlike older npn-pass transistor designs, where the minimum dropout voltage is limited by the base-to-emitter voltage drop and collector-to- emitter saturation voltage, dropout performance of the pnp output of these devices is limited only by the low v ce saturation voltage. a trade off for the low dropout voltage is a varying base drive requirement. micrel?s super eta pnp ? process reduces this drive requirement to only 2% to 5% of the load current. the mic37252 regulator is fully protected from damage due to fault conditions. current limiting is provided. this limiting is linear; output current during overload conditions is constant. thermal shutdown disables the device when the die temperature exceeds the maximum safe operating temperature. transient protection allows device (and load) survival ev en when the input voltage spikes above and below nominal. the output structure of these regulators allows voltages in excess of the desired output voltage to be applied wi thout reverse current flow. thermal design linear regulators are simple to use. the most complicated design parameters to consider are thermal characteristics. thermal design requires the following application-specific parameters: ? maximum ambient temperature (t a ) ? output current (i out ) ? output voltage (v out ) ? input voltage (v in ) ? ground current (i gnd ) first, calculate the power di ssipation of the regulator from these numbers and the device parameters from this datasheet. p d = (v in ? v out ) i out + v in i gnd where the ground current is approximated by using numbers from the ?electrical characteristics? or ?typical characteristics.? then the heat sink thermal resistance is determined with this formula: sa = ((t j(max) ? t a )/ p d ) ? ( jc + cs ) where t j(max) 125c and cs is between 0c and 2c/w. the heat sink may be significantly reduced in applications where the minimum input voltage is known and is large compared with the dropout voltage. use a series input resistor to drop excessive voltage and distribute the heat between this resistor and the regulator. the low dropout properties of micrel super eta pnp ? regulators allow significant reductions in regulator power dissipation and the associated heat sink without compromising performance. when this technique is employed, a capacitor of at least 1.0f is needed directly between the input and regulator ground. refer to application note 9 for further details and examples on thermal design and heat sink applications. output capacitor the mic37252 requires an output capacitor for stable operation. as a cap ldo, the mic37252 can operate with ceramic output capacitors as long as the amount of capacitance is 47f or greater. for values of output capacitance lower than 47f, the recommended esr range is 200m ? to 2 ? . the minimum value of output capacitance recommended for themic37252 is 10f. for 47f or greater the esr range recommended is less than1 ? . ultra-low esr, ceramic capacitors are recommended for output capacitance of 47f or greater to help improve transient response and noise reduction at high frequency. x7r/x5r dielectric-type ceramic capacitors are recommended because of their temperature performance. x7r-type capacitors change capacitance by 15% over their operating temperature range and are the most stable type of ceramic capacitors. z5u and y5v dielectric capacitors change value by as much as 50% and 60% respectively over their operating temperature ranges. to use a ceramic chip capacitor withy5v dielectric, the value must be much higher than an x7rceramic capacitor to ensure the same minimum capacitance over the equivalent operating temperature r ange. the mic37252 has excellent transient response to variations in input voltage and load current. the device has been designed to respond quickly to load current variations and input voltage variations. large output capacitors are not required to obtain this performance. a standard 47f output capacitor is all that is required. larger values help to improve performance even further. input capacitor an input capacitor of 1.0f or greater is recommended when the device is more than 4 inches away from the bulk supply capacitance, or when the supply is a battery. small, surface-mount chip capacitors can be used for the bypassing. the capacitor s hould be place within 1? of the device for optimal performance. larger values will help to improve ripple rejection by bypassing the input to the regulator, further improvi ng the integrity of the output voltage.
micrel, inc. mic37252 february 2006 7 m9999-021606 (408) 955-1690 transient response and 5v to 3.3v or 3.3v to 1.8vconversions the mic37252 has excellent transient response to variations in input volt age and load current. the device has been designed to respond quickly to load current variations and input voltage variations. large output capacitors are not required to obtain this performance. a standard 10f output capaci tor, preferably tantalum, is all that is required. larger values help to improve performance even further. by virtue of its low dropout voltage, this device does not saturate into dropout as readily as similar npn-based designs. when converting from 3.3v to 1.8v, the npn- based regulators are already operating in dropout, with typical dropout requirements of 2v or greater. to convert down to1.8v without operating in dropout, npn-based regulators require an input voltage of 3.8v at the very least. the mic37252 regulator will provide excellent performance with an input as low as 3.0v. this gives the pnp-based regulators a dist inct advantage over older npn-based linear regulators. minimum load current the mic37252 regulator is specified between finite loads. if the output current is too small, leakage currents dominate and the output voltage rises. a 10ma minimum load current is necessary for proper operation. enable input the mic37252 also features an enable input for on/off control of the device. its shutdown state draws ?zero? current (only microamperes of leakage). the enable input is ttl/cmos compatible for simple logic interface, but can be connected to up to vin. when enabled, it draws approximately 15a. adjustable regulator design figure 2. adjustable regulator with resistors the mic37252 allows progra mming of the output voltage anywhere between 1.24v and the 5.5v maximum operating rating of the family. two resistors are used. resistors values are recommended to be less than 10k ? in value to improve stability. the resistor values can be sized to draw the mini-mum load current for this device. the resistor values are calculated by: ? ? ? ? ? ? ? ? ? = 1 1.240 v r2 r1 out where v out is the desired output voltage. figure 2 shows component definition. applications with widely varying load currents may scale the resistors to draw the minimum load current required for proper operation (see above).
micrel, inc. mic37252 february 2006 8 m9999-021606 (408) 955-1690 package information 5-pin s-pak (r) 1 1 3 4 1 2 3 4 2 1 5-pin to-263 (u) 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 app liances, 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 purchaser?s use or sale of micrel produc ts for use in life support app liances, devices or systems is a purchaser?s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2002 micrel, incorporated.
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