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february 2005 1 mic3975 mic3975 micrel ordering information part number standard pb-free voltage junction temp. range package mic3975-1.65bmm mic3975-1.65ymm 1.65v C40c to +125c msop-8 mic3975-1.8bmm mic3975-1.8ymm 1.8v C40c to +125c msop-8 mic3975-2.5bmm mic3975-2.5ymm 2.5v C40c to +125c msop-8 mic3975-3.0bmm mic3975-3.0ymm 3.0v C40c to +125c msop-8 mic3975-3.3bmm mic3975-3.3ymm 3.3v C40c to +125c msop-8 mic3975-5.0bmm mic3975-5.0ymm 5.0v C40c to +125c msop-8 mic3975bmm mic3975ymm adj. C40c to +125c msop-8 mic3975 750ma cap low-voltage low-dropout regulator general description the mic3975 is a 750ma low-dropout linear voltage regula - tors that provide low-voltage, high-current output from an extremely small package. utilizing micrels proprietary super eta pnp? pass element, the mic3975 offers extremely low dropout (typically 300mv at 750ma) and low ground current (typically 6.5ma at 750ma). the mic3975 is ideal for pc add-in cards that need to con - vert from standard 5v to 3.3v or 3.0v, 3.3v to 2.5v or 2.5v to 1.8v or 1.65v. a guaranteed maximum dropout voltage of 500mv over all operating conditions allows the mic3975 to provide 2.5v from a supply as low as 3.0v and 1.8v or 1.65v from a supply as low as 2.25v. the mic3975 is fully protected with overcurrent limiting, thermal shutdown, and reversed-battery protection. fixed voltages of 5.0v, 3.3v, 3.0, 2.5v, 1.8v, and 1.65v are avail - able. an adjustable output voltage option is available for voltages down to 1.24v. for other voltages, contact micrel. typical applications features ? fixed and adjustable output voltages to 1.24v ? 300mv typical dropout at 750ma ideal for 3.0v to 2.5v conversion ideal for 2.5v to 1.8v or 1.65v conversion ? stable with ceramic capacitor ? 750ma minimum guaranteed output current ? 1% initial accuracy ? low ground current ? current limiting and thermal shutdown ? reversed-battery protection ? reversed-leakage protection ? fast transient response ? low-pro?le msop-8 applications ? fiber optic modules ? ldo linear regulator for pc add-in cards ? powerpc? power supplies ? high-ef?ciency linear power supplies ? smps post regulator ? multimedia and pc processor supplies ? battery chargers ? low-voltage microcontrollers and digital logic super eta pnp is a trademark 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 in r1 100k 2.5v error flag output v in 3.3v 10 ? f ceramic en out flg gnd mic3975-2.5bmm enable shutdown 2.5v/750ma regulator with error flag in r1 1.5v v in 2.5v 10 ? f ceramic r2 en out adj gnd mic3975bmm enable shutdown 1.5v/750ma adjustable regulator
mic3975 micrel mic3975 2 february 2005 pin con?guration 1 en in flg out 8 gnd gnd gnd gnd 7 6 5 2 3 4 mic3975-x.x fixed msop-8 (mm) 1 en in adj out 8 gnd gnd gnd gnd 7 6 5 2 3 4 adjustable pin description pin no. pin no. pin name pin function fixed adjustable 1 1 en enable (input): cmos-compatible control input. logic high = enable, logic low or open = shutdown. 2 2 in supply (input) 3 flg flag (output): open-collector error ?ag output. active low = output under - voltage. 3 adj adjustment input: feedback input. connect to resistive voltage-divider net - work. 4 4 out regulator output 5C8 5C8 gnd ground
february 2005 3 mic3975 mic3975 micrel electrical characteristics (note 12) v in = v out + 1v; v en = 2.25v; t j = 25c, bold values indicate C40c t j +125c; unless noted symbol parameter condition min typ max units v out output voltage 10ma C1 1 % 10ma i out 750ma, v out + 1v v in 8v C2 2 % line regulation i out = 10ma, v out + 1v v in 16v 0.06 0.5 % load regulation v in = v out + 1v, 10ma i out 750ma, 0.2 1 % v out /t output voltage temp. coef?cient, 40 100 ppm/c note 5 v do dropout voltage, note 6 i out = 100ma, v out = C1% 140 200 mv 250 mv i out = 500ma, v out = C1% 225 mv i out = 750ma, v out = C1% 300 500 mv i gnd ground current, note 7 i out = 100ma, v in = v out + 1v 400 a i out = 500ma, v in = v out + 1v 4 ma i out = 750ma, v in = v out + 1v 7.5 15 ma i out(lim) current limit v out = 0v, v in = v out + 1v 1.8 2.5 a enable input v en enable input voltage logic low (off) 0.8 v logic high (on) 2.25 v i en enable input current v en = 2.25v 1 15 30 a 75 a v en = 0.8v 2 a 4 a flag output i flg(leak) output leakage current v oh = 16v 0.01 1 a 2 a v flg(do) output low voltage v in = 2.250v, i ol , = 250a, note 9 210 300 mv 400 mv v flg low threshold % of v out 93 % high threshold % of v out 99.2 % hysteresis 1 % absolute maximum ratings (note 1) supply voltage (v in ) ....................................... C20v to +20v enable voltage (v en ) .................................................. +20v storage temperature (t s ) ........................ C65c to +150c lead temperature (soldering, 5 sec.) ........................ 260c esd, note 3 operating ratings (note 2) supply voltage (v in ) ................................... +2.25v to +16v enable voltage (v en ) .................................................. +16v maximum power dissipation (p d(max) ) ..................... note 4 junction temperature (t j ) ........................ C40c to +125c package thermal resistance msop-8 ( ja ) ...................................................... 80c/w
mic3975 micrel mic3975 4 february 2005 symbol parameter condition min typ max units adjustable output only reference voltage 1.228 1.240 1.252 v 1.215 1.265 v note 10 1.203 1.277 v adjust pin bias current 40 80 na 120 na reference voltage note 11 20 ppm/c temp. coef?cient adjust pin bias current 0.1 na/c temp. coef?cient note 1. exceeding the absolute maximum ratings may damage the device. note 2. the device is not guaranteed to function outside its operating rating. note 3. devices are esd sensitive. handling precautions recommended. note 4. p d(max) = (t j(max) C t a ) ja , where ja depends upon the printed circuit layout. see applications information. note 5. output voltage temperature coef?cient is v out(worst case) (t j(max) C t j(min) ) where t j(max) is +125c and t j(min) is C40c. note 6. v do = v in C v out when v out decreases to 98% of its nominal output voltage with v in = v out + 1v. for output voltages below 2.25v, dropout voltage is the input-to-output voltage differential with the minimum input voltage being 2.25v. minimum input operating voltage is 2.25v. note 7. i gnd is the quiescent current. i in = i gnd + i out . note 8. v en 0.8v, v in 8v, and v out = 0v. note 9. for a 2.5v device, v in = 2.250v (device is in dropout). note 10. v ref v out (v in C 1v), 2.25v v in 16v, 10ma i l 750ma, t j = t max . note 11. thermal regulation is de?ned as the change in output voltage at a time t after a change in power dissipation is applied, excluding load or line regulation effects. speci?cations are for a 200ma load pulse at v in = 16v for t = 10ms. note 12. speci?cation for packaged product only.
february 2005 5 mic3975 mic3975 micrel typical characteristics
mic3975 micrel mic3975 6 february 2005
february 2005 7 mic3975 mic3975 micrel functional characteristics load transient response time (200 ? s/div.) load current (500ma/div.) output voltage (200mv/div.) v in = 3.3v v out = 2.5v c out = 10 ?f ceramic 750ma 100ma load transient response time (200 ? s/div.) load current (500ma/div.) output voltage (200mv/div.) v in = 3.3v v out = 2.5v c out = 10 ?f ceramic 750ma 10ma v out = 2.5v c out = 10 ?f ceramic i load = 10ma 3.3v 5.0v line transient response time (200 ? s/div.) input voltage (1v/div.) output voltage (50mv/div.)
mic3975 micrel mic3975 8 february 2005 functional diagrams ref. 18v o.v. i limit thermal shut- down 1.240v 1.180v en in flag gnd out mic3975 fixed regulator with flag and enable block diagram ref. 18v o.v. i limit thermal shut- down 1.240v en in gnd out adj mic3975 adjustable regulator block diagram
february 2005 9 mic3975 mic3975 micrel applications information the mic3975 is a high-performance low-dropout voltage regu - lator suitable for moderate to high-current voltage regulator applications. its 500mv dropout voltage at full load and over - temperature makes it especially valuable in battery-powered systems and as high-ef?ciency noise ?lters in post-regulator applications. unlike older npn-pass transistor designs, where the minimum dropout voltage is limited by the base-to-emit - ter 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. micrels super eta pnp? process reduces this drive requirement to only 2% of the load current. the mic3975 regulator is fully protected from damage due to fault conditions. linear current limiting is provided. output cur - rent 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 even when the input volt - age spikes above and below nominal. the output structure of these regulators allows voltages in excess of the desired output voltage to be applied without reverse current ?ow. mic3975x.x in out gnd c in c out v in v out figure 1. capacitor requirements output capacitor the mic3975 requires an output capacitor for stable opera - tion. as a cap ldo, the mic3975 can operate with ceramic output capacitors as long as the amount of capacitance is 10 f or greater. for values of output capacitance lower than 10 f, the recommended esr range is 200m ? to 2 ? . the minimum value of output capacitance recommended for the mic3975 is 4.7 f. for 10 f or greater the esr range recommended is less than 1 ? . ultra-low esr ceramic capacitors are recommended for output capacitance of 10 f or greater to help improve transient response and noise reduction at high frequency. x7r/x5r dielectric-type ceramic capacitors are recom - mended 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 operat - ing temperature ranges. to use a ceramic chip capacitor with y5v dielectric, the value must be much higher than an x7r ceramic capacitor to ensure the same minimum capacitance over the equivalent operating temperature range. input capacitor an input capacitor of 1f or greater is recommended when the device is more than 4 inches away from the bulk ac supply capacitance or when the supply is a battery. small, surface mount, ceramic chip capacitors can be used for bypassing. larger values will help to improve ripple rejection by bypass - ing the input to the regulator, further improving the integrity of the output voltage. error flag the mic3975 features an error ?ag (flg), which monitors the output voltage and signals an error condition when this voltage drops 5% below its expected value. the error ?ag is an open-collector output that pulls low under fault conditions and may sink up to 10ma. low output voltage signi?es a number of possible problems, including an overcurrent fault (the device is in current limit) or low input voltage. the ?ag output is inoperative during overtemperature conditions. a pull-up resistor from flg to either v in or v out is required for proper operation. for information regarding the minimum and maximum values of pull-up resistance, refer to the graph in the typical characteristics section of the data sheet. enable input the mic3975 features an active-high enable input (en) that allows on-off control of the regulator. current drain reduces to zero when the device is shutdown, with only microamperes of leakage current. the en input has ttl/cmos compatible thresholds for simple logic interfacing. en may be directly tied to v in and pulled up to the maximum supply voltage transient response and 3.3v to 2.5v or 2.5v to 1.8v or 1.65v conversion the mic3975 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 10f output capacitor, is all that is required. larger values help to improve performance even further. by virtue of its low-dropout voltage, this device does not satu - rate into dropout as readily as similar npn-based designs. when converting from 3.3v to 2.5v or 2.5v to 1.8v or 1.65v, the npn based regulators are already operating in dropout, with typical dropout requirements of 1.2v or greater. to convert down to 2.5v or 1.8v without operating in dropout, npn-based regulators require an input voltage of 3.7v at the very least. the mic3975 regulator will provide excellent performance with an input as low as 3.0v or 2.5v respectively. this gives the pnp based regulators a distinct advantage over older, npn based linear regulators. minimum load current the mic3975 regulator is speci?ed between ?nite 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 regulation.
mic3975 micrel mic3975 10 february 2005 adjustable regulator design in r1 v out v in c out r2 en out adj gnd mic3975 enable shutdown v 1.240v 1 r1 r2 out ? ? ? ? ? ? ? ? figure 2. adjustable regulator with resistors the mic3975 allows programming the output voltage any - where between 1.24v and the 16v maximum operating rating of the family. two resistors are used. resistors can be quite large, up to 1m, because of the very high input impedance and low bias current of the sense comparator: the resistor values are calculated by: r1 r2 v 1.240 1 out ? ? ? ? ? ? ? ? where v o is the desired output voltage. figure 2 shows component de?nition. applications with widely varying load currents may scale the resistors to draw the minimum load current required for proper operation (see above). power msop-8 thermal characteristics one of the secrets of the mic3975s performance is its power mso-8 package featuring half the thermal resistance of a standard mso-8 package. lower thermal resistance means more output current or higher input voltage for a given pack - age size. lower thermal resistance is achieved by joining the four ground leads with the die attach paddle to create a single- piece electrical and thermal conductor. this concept has been used by mosfet manufacturers for years, proving very reliable and cost effective for the user. thermal resistance consists of two main elements, jc (junc - tion-to-case thermal resistance) and ca (case-to-ambient thermal resistance). see figure 3. jc is the resistance from the die to the leads of the package. ca is the resistance from the leads to the ambient air and it includes cs (case- to-sink thermal resistance) and sa (sink-to-ambient thermal resistance). using the power msop-8 reduces the jc dramatically and allows the user to reduce ca . the total thermal resistance, ja (junction-to-ambient thermal resistance) is the limiting factor in calculating the maximum power dissipation capabil - ity of the device. typically, the power msop-8 has a ja of 80c/w, this is signi?cantly lower than the standard msop-8 which is typically 160c/w. ca is reduced because pins 5 through 8 can now be soldered directly to a ground plane which signi?cantly reduces the case-to-sink thermal resistance and sink to ambient thermal resistance. low-dropout linear regulators from micrel are rated to a maximum junction temperature of 125c. it is important not to exceed this maximum junction temperature during operation of the device. to prevent this maximum junction temperature from being exceeded, the appropriate ground plane heat sink must be used. ? ja ? jc ? ca printed circuit board ground plane heat sink area msop-8 ambient figure 3. thermal resistance figure 4 shows copper area versus power dissipation with each trace corresponding to a different temperature rise above ambient. from these curves, the minimum area of copper necessary for the part to operate safely can be determined. the maximum allowable temperature rise must be calculated to determine operation along which curve. t = t j(max) C t a(max) t j(max) = 125c figure 4. copper area vs. power-msop power dissipation ( ? t ja ) figure 5. copper area vs. power-msop power dissipation (t a )
february 2005 11 mic3975 mic3975 micrel t a(max) = maximum ambient operating temperature for example, the maximum ambient temperature is 50c, the t is determined as follows: t = 125c C 50c t = 75c using figure 4, the minimum amount of required copper can be determined based on the required power dissipation. power dissipation in a linear regulator is calculated as follows: p d = (v in C v out ) i out + v in i gnd if we use a 2.5v output device and a 3.3v input at an output current of 750ma, then our power dissipation is as follows: p d = (3.3v C 2.5v) 750ma + 3.3v 7.5ma p d = 600mw + 25mw p d = 625mw from figure 4, the minimum amount of copper required to operate this application at a t of 75c is 160mm 2 . quick method determine the power dissipation requirements for the design along with the maximum ambient temperature at which the device will be operated. refer to figure 5, which shows safe operating curves for three different ambient temperatures: 25c, 50c and 85c. from these curves, the minimum amount of copper can be determined by knowing the maxi - mum power dissipation required. if the maximum ambient temperature is 50c and the power dissipation is as above, 625mw, the curve in figure 5 shows that the required area of copper is 160mm 2 . the ja of this package is ideally 80c/w, but it will vary depending upon the availability of copper ground plane to which it is attached.
mic3975 micrel mic3975 12 february 2005 package information 8-lead msop (mm) 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 datasheet is believed to be accurate and reliable. however , no responsibility is assumed by micrel for its use. micrel reserves the right to change circuitry and speci?cations at any time without noti?cation to the customer. micrel products are noth reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intended 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 signi? cant injury to the user. a purchasers use or sale of micrel products for use in life support appliances, devices or systems is at purchaser s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2005 micrel, incorporated.

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