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1 lt1307/lt1307b 1307fa single cell micropower 600khz pwm dc/dc converters the lt ? 1307/lt1307b are micropower, fixed frequency dc/dc converters that operate from an input voltage as low as 1v. first in the industry to achieve true current mode pwm performance from a single cell supply, the lt1307 features automatic shifting to power saving burst mode operation at light loads. high efficiency is main- tained over a broad 100 m a to 100ma load range. the lt1307b does not shift into burst mode operation at light loads, eliminating low frequency output ripple at the expense of light load efficiency. the devices contain a low- battery detector with a 200mv reference and shut down to less than 5 m a. no load quiescent current of the lt1307 is 50 m a and the internal npn power switch handles a 500ma current with a voltage drop of just 295mv. unlike competitive devices, large electrolytic capacitors are not required with the lt1307/lt1307b in single cell applications. the high frequency (600khz) switching al- lows the use of tiny surface mount multilayer ceramic (mlc) capacitors along with small surface mount induc- tors. the devices work with just 10 m f of output capaci- tance and require only 1 m f of input bypassing. the lt1307/lt1307b are available in 8-lead msop, pdip and so packages. n uses small ceramic capacitors n 50 m a quiescent current (lt1307) n 1ma quiescent current (lt1307b) n operates with v in as low as 1v n 600khz fixed frequency operation n starts into full load n low shutdown current: 3 m a n low-battery detector n 3.3v at 75ma from a single cell n automatic burst mode ? operation at light load (lt1307) n continuous switching at light load (lt1307b) n low v cesat switch: 295mv at 500ma n pagers n cordless telephones n gps receivers n battery backup n portable electronic equipment n glucose meters n diagnostic medical instrumentation burst mode is a registered trademark of linear technology corporation. , ltc and lt are registered trademarks of linear technology corporation. single cell to 3.3v converter efficiency load current (ma) 0.1 70 efficiency (%) 80 90 1 10 100 1307 ta01 60 50 v in = 1.5v v in = 1v v in = 1.25v v in sw fb lt1307 l1 10 m h d1 lbo lbi shdn shutdown 100k r2 604k 1% 3.3v 75ma r1 1.02m 1% 680pf for 5v output: r1 = 1m, r2 = 329k c1: murata-erie grm235y5v105z01 marcon thcs50e1e105z tokin 1e105zy5u-c103-f c2: murata-erie grm235y5v106z01 marcon thcs50e1e105z tokin 1e106zy5u-c304-f 1307 f01 c1 1 m f c2 10 m f 1.5v cell v c gnd d1: motorola mbr0520l l1: coilcraft d01608c-103 sumida cd43-100 murata erie lqh3c100 figure 1. single cell to 3.3v boost converter features descriptio u applicatio s u typical applicatio u
2 lt1307/lt1307b 1307fa v in , shdn, lbo voltage ......................................... 12v sw voltage ............................................................. 30v fb voltage ....................................................... v in + 1v v c voltage ................................................................ 2v lbi voltage ............................................ 0v v lbi 1v current into fb pin .............................................. 1ma junction temperature ........................................... 125 c operating temperature range commercial (note 2) ......................... C 20 c to 70 c industrial ........................................... C 40 c to 85 c storage temperature range ................ C 65 c to 150 c lead temperature (soldering, 10 sec)................. 300 c t jmax = 125 c, q ja = 160 c/w order part number order part number 1 2 3 4 v c fb shdn gnd 8 7 6 5 lbo lbi v in sw top view ms8 package 8-lead plastic msop 1 2 3 4 8 7 6 5 top view lbo lbi v in sw v c fb shdn gnd n8 package 8-lead pdip s8 package 8-lead plastic so lt1307cms8 lt1307bcms8 lt1307cn8 lt1307cs8 lt1307is8 lt1307bcs8 lt1307bis8 t jmax = 125 c, q ja = 100 c/w (n8) t jmax = 125 c, q ja = 120 c/w (s8) s8 part marking 1307 1307b 1307i 1307bi ms8 part marking the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. commercial grade 0 c to 70 c. v in = 1.1v, v shdn = v in , lt1307/lt1307b unless otherwise noted. symbol parameter conditions min typ max units i q quiescent current not switching (lt1307) l 50 90 m a not switching (lt1307b) l 1.0 1.5 ma v shdn = 0v l 13 m a v fb feedback voltage l 1.20 1.22 1.24 v i b fb pin bias current (note 3) v fb = v ref l 27 60 na reference line regulation 1v v in 2v (25 c, 0 c) 0.6 1.1 %/v 1v v in 2v (70 c) 1.5 %/v 2v v in 5v l 0.3 0.8 %/v minimum input voltage 0.92 1 v input voltage range l 15v g m error amp transconductance d i = 5 m a l 25 35 65 m mhos a v error amp voltage gain 25 c, 0 c 35 100 v/v 70 c 30 v/v f osc switching frequency l 550 600 750 khz ltic ltib consult ltc marketing for parts specified with wider operating temperature ranges. (note 1) absolute axi u rati gs w ww u package/order i for atio uu w electrical characteristics
3 lt1307/lt1307b 1307fa symbol parameter conditions min typ max units maximum duty cycle 25 c, 0 c8084% 70 c76% switch current limit (note 4) dc = 40% l 0.6 1.25 a dc = 75% 0.5 a switch v cesat i sw = 500ma (25 c, 0 c) 295 350 mv i sw = 500ma (70 c) 400 mv burst mode operation switch current limit l = 10 m h 100 ma (lt1307 only) l = 22 m h50ma shutdown pin current v shdn = v in l 2.5 4.0 m a v shdn = 0v l C 1.5 C 2.5 m a lbi threshold voltage l 190 200 210 mv lbo output low i sink = 10 m a l 0.1 0.25 v lbo leakage current v lbi = 250mv, v lbo = 5v l 0.01 0.1 m a lbi input bias current (note 5) v lbi = 150mv l 525na low-battery detector gain 1m w load (25 c, 0 c) 1000 3000 v/v 1m w load (70 c) 500 v/v switch leakage current v sw = 5v l 0.01 3 m a reverse battery current (note 6) 750 ma commercial grade t a = C 20 c, v in = 1.1v, v shdn = v in , unless otherwise noted (note 2). symbol parameter conditions min typ max units i q quiescent current v fb = 1.3v, not switching (lt1307) 50 100 m a v fb = 1.3v, not switching (lt1307b) 1.1 1.6 ma v shdn = 0v 1 3 m a v fb feedback voltage 1.195 1.22 1.245 v g m error amp transconductance d i = 5 m a253565 m mhos a v error amp voltage gain 35 100 v/v f osc switching frequency 500 600 750 khz maximum duty cycle 80 84 % switch v cesat i sw = 500ma, v in = 1.2v 250 350 mv shutdown pin current v shdn = v in 2.5 4.0 m a v shdn = 0v C 1.5 C 2.5 m a lbi threshold voltage 186 200 210 mv the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. commercial grade 0 c to 70 c. v in = 1.1v, v shdn = v in , lt1307/lt1307b unless otherwise noted. electrical characteristics
4 lt1307/lt1307b 1307fa e lectr ic al c c hara terist ics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. industrial grade C 40 c to 85 c. v in = 1.1v, v shdn = v in , lt1307/lt1307b unless otherwise noted. symbol parameter conditions min typ max units i q quiescent current v fb = 1.3v, not switching (lt1307) l 50 100 m a v fb = 1.3v, not switching (lt1307b) l 1 1.8 ma v shdn = 0v l 13 m a v fb feedback voltage l 1.195 1.22 1.245 v i b fb pin bias current (note 3) v fb = v ref l 10 27 100 na reference line regulation 1v v in 2v (C 40 c) 0.6 1.1 %/v 1v v in 2v (85 c) 3.2 %/v 2v v in 5v l 0.3 0.8 %/v minimum input voltage C 40 c 1.1 1.2 v 85 c 0.8 1.0 v input voltage range l 5v g m error amp transconductance d i = 5 m a l 25 35 65 m mhos a v error amp voltage gain C 40 c35v/v 85 c30v/v f osc switching frequency l 500 600 750 khz maximum duty cycle C 40 c8084% 85 c7580% switch current limit (note 4) dc = 40% l 0.6 1.25 a dc = 75% 0.5 a switch v cesat i sw = 500ma, v in = 1.2v (C 40 c) 250 350 mv i sw = 500ma (85 c) 330 400 mv burst mode operation switch current limit l = 10 m h 100 ma (lt1307 only) l = 22 m h50ma shutdown pin current v shdn = v in l 2.5 4.0 m a v shdn = 0v l C 1.5 C 2.5 m a lbi threshold voltage l 186 200 210 mv lbo output low i sink = 10 m a l 0.1 0.25 v lbo leakage current v lbi = 250mv, v lbo = 5v l 0.1 0.3 m a lbi input bias current (note 5) v lbi = 150mv l 530na low-battery detector gain 1m w load (C 40 c) 1000 6000 v/v 1m w load (85 c) 400 v/v switch leakage current v sw = 5v l 0.01 3 m a note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: specifications for commercial (c) grade devices are guaranteed but not tested at C 20 c. ms8 package devices are designed for and intended to meet commercial temperature range specifications but are not tested at C 20 c or 0 c. note 3: bias current flows into fb pin. note 4: switch current limit guaranteed by design and/or correlation to static tests. duty cycle affects current limit due to ramp generator. note 5: bias current flows out of lbi pin. note 6: the lt1307/lt1307b will withstand continuous application of 1.6v applied to the gnd pin while v in and sw are grounded.
5 lt1307/lt1307b 1307fa load current (ma) 50 60 70 80 90 efficiency (%) 200 0.1 1 10 100 lt1307 ?g01 v in = 1.00v v in = 1.25v v in = 1.5v 3.3v output efficiency, circuit of figure 1 (lt1307b) 5v output efficiency, circuit of figure 1 (lt1307b) quiescent current vs temperature feedback bias current vs temperature lbi bias current vs temperature 5v output efficiency, circuit of figure 1 (lt1307) temperature ( c) ?0 quiescent current ( a) 30 40 50 25 75 1307 g04 20 10 0 ?5 0 50 60 70 80 100 temperature ( c) ?0 0 feedback bias current (na) 10 20 30 40 50 ?5 02550 1307 g05 75 100 v in = 1.1v temperature ( c) ?0 lbi bias current (na) 25 75 lt1307 ?tpc06 ?5 0 50 16 14 12 10 8 6 4 2 0 100 quiescent current in shutdown shutdown pin bias current vs input voltage switch v cesat vs current input voltage (v) 0 quiescent current ( a) 6 8 10 4 1307 g07 4 2 0 1 2 3 5 input voltage (v) 0 shutdown pin current ( a) 12 16 20 4 1307 g07 8 4 0 1 2 3 5 switch current (ma) 0 0 v cesat (mv) 100 200 300 400 500 100 200 300 400 lt1307 ?tpc09 500 600 t a = 25 c load current (ma) 0.1 50 efficiency (%) 70 90 100 10 1 1307 g02 30 40 60 80 20 10 v in = 1.25v v in = 1.5v v in = 1v typical perfor a ce characteristics uw load current (ma) 0.1 50 efficiency (%) 70 90 100 10 1 1307 g02 30 40 60 80 20 10 v in = 1.5v v in = 1v v in = 1.25v
6 lt1307/lt1307b 1307fa feedback voltage vs temperature lbi reference vs temperature oscillator frequency vs input voltage temperature ( c) ?0 1.200 feedback voltage (v) 1.205 1.210 1.215 1.220 1.230 ?5 02550 1307 g10 75 100 1.225 v in = 1.25v 500 m s/div 1307 g13 v out = 3.3v transient response (lt1307) i l 200ma/div v out 200mv/div ac coupled 55ma 5ma i load v in = 0.92v i load 10ma/div 1307 g15 v out = 3.3v load regulation (lt1307) v out 50mv/div dc coupled offset added temperature ( c) ?0 reference voltage (mv) ?5 0 25 50 lt1307 ?tpc11 75 210 208 206 204 202 200 198 196 194 192 190 100 v in = 1.25v 500 m s/div 1307 g14 v out = 3.3v transient response (lt1307b) i l 200ma/div v out 200mv/div ac coupled 55ma 5ma v in = 1.15v i load 20ma/div 1307 g17 v out = 3.3v load regulation (lt1307) v in = 1v i load 10ma/div 1307 g18 v out = 5v load regulation (lt1307) v out 50mv/div dc coupled offset added v out 50mv/div dc coupled offset added v in = 1v i load 20ma/div 1307 g16 v out = 3.3v load regulation (lt1307) v out 50mv/div dc coupled offset added load regulation (lt1307) i load v in = 1.25v 100 m s/div 1307 g21 v out = 5v i load = 1.5ma i l 100ma/div v sw 5v/div v out 50mv/div ac coupled v out 50mv/div ac coupled v in = 1.25v 100 m s/div 1307 g20 v out = 5v i load = 1.5ma i l 100ma/div v sw 5v/div v out 50mv/div dc coupled offset added v in = 1.15v i load 10ma/div 1307 g19 v out = 5v circuit operation, l = 22 m h (lt1307) circuit operation, l = 10 m h (lt1307) input voltage (v) 1 frequency (khz) 600 700 5 lt1307 ?tpc12 500 400 2 3 4 900 800 85 c ?0 c 25 c typical perfor a ce characteristics uw
7 lt1307/lt1307b 1307fa v c (pin 1): compensation pin for error amplifier. con- nect a series rc from this pin to ground. typical values are 100k w and 680pf. minimize trace area at v c . fb (pin 2): feedback pin. reference voltage is 1.22v. connect resistor divider tap here. minimize trace area at fb. set v out according to: v out = 1.22v(1 + r1/r2). shdn (pin 3): shutdown. ground this pin to turn off switcher. must be tied to v in (or higher voltage) to enable switcher. do not float the shdn pin. gnd (pin 4): ground. connect directly to local ground plane. sw (pin 5): switch pin. connect inductor/diode here. minimize trace area at this pin to keep emi down. v in (pin 6): supply pin. must have 1 m f ceramic bypass capacitor right at the pin, connected directly to ground. lbi (pin 7): low-battery detector input. 200mv refer- ence. voltage on lbi must stay between ground and 700mv. lbo (pin 8): low-battery detector output. open collec- tor, can sink 10 m a. a 1m w pull-up is recommended. figure 2. lt1307/lt1307b block diagram + + + + + + + s comparator ramp generator r bias v c g m q2 10 q1 fb fb enable 200mv a = 3 ff a2 a1 error amplifier a4 0.15 w driver sw gnd 1307 f02 q3 q s 600khz oscillator 5 lbo lbi shdn shutdown 3 7 1 4 r6 40k r5 40k r1 (external) r3 30k r4 140k 2 v in v in v out 6 8 r2 (external) *hysteresis in lt1307 only * uu u pi fu ctio s block diagra w
8 lt1307/lt1307b 1307fa operation the lt1307 combines a current mode, fixed frequency pwm architecture with burst mode micropower operation to maintain high efficiency at light loads. operation can best be understood by referring to the block diagram in figure 2. q1 and q2 form a bandgap reference core whose loop is closed around the output of the converter. when v in is 1v, the feedback voltage of 1.22v, along with an 80mv drop across r5 and r6, forward biases q1 and q2s base collector junctions to 300mv. because this is not enough to saturate either transistor, fb can be at a higher voltage than v in . when there is no load, fb rises slightly above 1.22v, causing v c (the error amplifiers output) to decrease. when v c reaches the bias voltage on hysteretic comparator a1, a1s output goes low, turning off all circuitry except the input stage, error amplifier and low- battery detector. total current consumption in this state is 50 m a. as output loading causes the fb voltage to de- crease, a1s output goes high, enabling the rest of the ic. switch current is limited to approximately 100ma initially after a1s output goes high. if the load is light, the output voltage (and fb voltage) will increase until a1s output goes low, turning off the rest of the lt1307. low fre- quency ripple voltage appears at the output. the ripple frequency is dependent on load current and output capaci- tance. this burst mode operation keeps the output regu- lated and reduces average current into the ic, resulting in high efficiency even at load currents of 100 m a or less. if the output load increases sufficiently, a1s output re- mains high, resulting in continuous operation. when the lt1307 is running continuously, peak switch current is controlled by v c to regulate the output voltage. the switch is turned on at the beginning of each switch cycle. when the summation of a signal representing switch current and a ramp generator (introduced to avoid subharmonic oscil- lations at duty factors greater than 50%) exceeds the v c signal, comparator a2 changes state, resetting the flip- flop and turning off the switch. output voltage increases as switch current is increased. the output, attenuated by a resistor divider, appears at the fb pin, closing the overall loop. frequency compensation is provided by an external series rc network connected between the v c pin and ground. low-battery detector a4s open collector output (lbo) pulls low when the lbi pin voltage drops below 200mv. there is no hysteresis in a4, allowing it to be used as an amplifier in some applications. the entire device is disabled when the shdn pin is brought low. to enable the converter, shdn must be at v in or at a higher voltage. the lt1307b differs from the lt1307 in that there is no hysteresis in comparator a1. also, the bias point on a1 is set lower than on the lt1307 so that switching can occur at inductor current less than 100ma. because a1 has no hysteresis, there is no burst mode operation at light loads and the device continues switching at constant frequency. this results in the absence of low frequency output voltage ripple at the expense of efficiency. the difference between the two devices is clearly illus- trated in figures 3 and 4. the top two traces in figure 3 show an lt1307/lt1307b circuit, using the components indicated in figure 1, set to a 5v output. input voltage is 1.25v. load current is stepped from 1ma to 41ma for both circuits. low frequency burst mode operation voltage ripple is observed on trace a, while none is observed on trace a trace b lt1307 v out 500mv/div ac coupled 41ma 1ma i l lt1307b v out 500mv/div ac coupled v in = 1.25v 1ms/div 1307 f03 v out = 5v figure 3. lt1307 exhibits burst mode operation ripple at 1ma load, lt1307b does not lt1307 v out 200mv/div ac coupled trace a 45ma 5ma i l lt1307b v out 200mv/div ac coupled trace b v in = 1.5v 500 m s/div 1307 f04 v out = 5v figure 4. at higher loading and a 1.5v supply, lt1307 again exhibits burst mode operation ripple at 5ma load, lt1307b does not applicatio s i for atio wu uu
9 lt1307/lt1307b 1307fa quite evident, as is this particular devices 575khz switch- ing frequency (nominal switching frequency is 600khz). note, however, the absence of significant energy at 455khz. figure 7s plot reduces the frequency span from 255khz to 655khz with a 455khz center. burst mode low frequency ripple creates sidebands around the 575khz switching fundamental. these sidebands have low signal amplitude at 455khz, measuring C 55dbmv rms . as load current is further reduced, the burst mode frequency decreases. this spaces the sidebands around the switching fre- quency closer together, moving spectral energy further trace b. similarly, figure 4 details the two circuits with a load step from 5ma to 45ma with a 1.5v input. the lt1307b also can be used in lower current applica- tions where a clean, low ripple output is needed. figure 5 details transient response of a single cell to 3.3v con- verter, using an inductor value of 100 m h. this high induc- tance minimizes ripple current, allowing the lt1307b to regulate without skipping cycles. as the load current is stepped from 5ma to 10ma, the output voltage responds cleanly. note that the v c pin loop compensation has been made more conservative (increased c, decreased r). figure 5. increasing l to 100 m h, along with r c = 36k, c c = 20nf and c out = 10 m f, low noise performance of lt1307b can be realized at light loads of 5ma to 10ma 10ma 5ma i l v in = 1.25v 1ms/div 1307 f05 v out = 3.3v i l 20ma/div v out 100mv/div ac coupled at light loads, the lt1307b will begin to skip alternate cycles. the load point at which this occurs can be de- creased by increasing the inductor value. however, output ripple will continue to be significantly less than the lt1307 output ripple. further, the lt1307b can be forced into micropower mode, where i q falls from 1ma to 50 m a by pulling down v c to 0.3v or less externally. dc/dc converter noise considerations switching regulator noise is a significant concern in many communications systems. the lt1307 is designed to keep noise energy out of the sensitive 455khz band at all load levels while consuming only 60 m w to 100 m w at no load. at light load levels, the device is in burst mode, causing low frequency ripple to appear at the output. figure 6 details spectral noise directly at the output of figure 1s circuit in a 1khz to 1mhz bandwidth. the converter supplies a 5ma load from a 1.25v input. the burst mode fundamental at 5.1khz and its harmonics are frequency (khz) 1 output noise voltage (dbmv rms ) 40 30 20 10 0 ?0 ?0 ?0 ?0 ?0 ?0 10 100 1000 1307 f06 rbw = 100hz figure 6. spectral noise plot of 3.3v converter delivering 5ma load. burst mode fundamental at 5.1khz is 23dbmv rms or 14mv rms frequency (khz) 255 output noise voltage (dbmv rms ) ?0 ?5 ?0 ?5 ?0 ?5 ?0 ?5 ?0 ?5 ?0 455 1307 f07 655 rbw = 100hz figure 7. span centered at 455khz shows C 55dbmv rms (1.8 m v rms ) at 455khz. burst mode creates sidebands 5.1khz apart around the switching frequency fundamental of 575khz applicatio s i for atio wu uu
10 lt1307/lt1307b 1307fa to eliminate the low frequency noise of figure 6, the lt1307 can be replaced with the lt1307b. figure 9 details the spectral noise at the output of figure 1s circuit using an lt1307b at 5ma load. although spectral energy is present at 333khz due to alternate pulse skipping, all burst mode operation spectral components are gone. alternate pulse skipping can be eliminated by increasing inductance. frequency compensation obtaining proper values for the frequency compensation network is largely an empirical, iterative procedure, since variations in input and output voltage, topology, capacitor value and esr, and inductance make a simple formula elusive. as an example, consider the case of a 1.25v to 3.3v boost converter supplying 50ma. to determine optimum compensation, the circuit is built and a transient load is applied to the circuit. figure 10 shows the setup. away from 455khz. figure 8 shows the noise spectrum of the converter with the load increased to 20ma. the lt1307 shifts out of burst mode operation, eliminating low frequency ripple. spectral energy is present only at the switching fundamental and its harmonics. noise voltage measures C 5dbmv rms or 560 m v rms at the 575khz switching frequency, and is below C 60dbmv rms for all other frequencies in the range. by combining burst mode with fixed frequency operation, the lt1307 keeps noise away from 455khz. v in v out fb 1307 ?f10 gnd sw 1 m f 10 m h mbr0520l c r 590k 1m 50 w 66 w 3300 w 1.25v v c 10 m f* *ceramic shdn lt1307 figure 10. boost converter with simulated load figure 11a details transient response without compensa- tion components. although the output ripple voltage at a 1ma load is low, allowing the error amplifier to operate wideband results in excessive ripple at a 50ma load. some kind of loop stabilizing network is obviously required. a 100k/22nf series rc is connected to the v c pin, resulting in the response pictured in figure 11b. the output settles in about 7ms to 8ms. this may be acceptable, but we can do better. reducing c to 2nf gives figure 11cs response. this is clearly in the right direction. after another order of magnitude reduction, figure 11ds response shows some frequency (khz) 205 output voltage noise (dbmv rms ) 0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 100 lt1307 ?f09 455 705 figure 9. lt1307b at 5ma load shows no audio components or sidebands about switching frequency, 333khz fundamental amplitude is C10dbmv, or 316 m v rms frequency (khz) 255 output noise voltage (dbmv rms ) 0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 100 455 1307 f08 655 rbw = 100hz figure 8. with converter delivering 20ma, low frequency sidebands disappear. noise is present only at the 575khz switching frequency applicatio s i for atio wu uu
11 lt1307/lt1307b 1307fa 51ma 1ma i l 5ms/div 1307 f11a v out 200mv/div ac coupled figure 11a. v c pin left unconnected. output ripple voltage is 300mv p-p under load 51ma 1ma i l 5ms/div 1307 f11b figure 11b. inclusion of a 100k/22nf series rc on v c pin results in overdamped stable response v out 200mv/div ac coupled 51ma 1ma i l 1ms/div 1307 f11a v out 200mv/div ac coupled figure 11c. reducing c to 2nf speeds up response, although still overdamped 51ma 1ma i l 500 m s/div 1307 f11b figure 11d. a 100k/200pf series rc shows some underdamping v out 200mv/div ac coupled 51ma 1ma i l 1ms/div 1307 f11b figure 11e. a 100k/680pf rc provides optimum settling time with no ringing v out 200mv/div ac coupled pole, requiring added c at the v c pin network to prevent loop oscillation. observant readers will notice r has been set to 100k for all the photos in figure 11. usable r values can be found in the 10k to 500k range, but after too many trips to the resistor bins, 100k wins. underdamping. now settling time is about 300 m s. increas- ing c to 680pf results in the response shown in figure 11e. this response has minimum settling time with no over- shoot or underdamping. converters using a 2-cell input need more capacitance at the output. this added capacitance moves in the output applicatio s i for atio wu uu
12 lt1307/lt1307b 1307fa layout hints the lt1307 switches current at high speed, mandating careful attention to layout for proper performance. you will not get advertised performance with careless layouts. figure 12 shows recommended component placement. follow this closely in your pc layout. note the direct path of the switching loops. input capacitor c in must be placed close (< 5mm) to the ic package. as little as 10mm of wire or pc trace from c in to v in will cause problems such as inability to regulate or oscillation. a 1 m f ceramic bypass capacitor is the only input capacitance required provided the battery has a low inductance path to the circuit . the battery itself provides the bulk capacitance the device requires for proper operation. if the battery is located some distance from the circuit, an additional input capacitor may be required. a 100 m f aluminum electrolytic unit works well in these cases. this capacitor need not have low esr. component selection inductors inductors appropriate for use with the lt1307 must pos- sess three attributes. first, they must have low core loss at 600khz. most ferrite core units have acceptable losses at this switching frequency. inexpensive iron powder cores should be viewed suspiciously, as core losses can cause significant efficiency penalties at 600khz. second, the inductor must handle current of 500ma without saturat- ing. this places a lower limit on the physical size of the unit. molded chokes or chip inductors usually do not have enough core to support 500ma current and are unsuitable for the application. lastly, the inductor should have low dcr (copper wire resistance) to prevent efficiency-killing i 2 r losses. linear technology has identified several induc- tors suitable for use with the lt1307. this is not an exclusive list. there are many magnetics vendors whose components are suitable for use. a few vendors compo- nents are listed in table 1. table 1. inductors suitable for use with the lt1307 max height part value dcr mfr (mm) comment lqh3c100 10 m h 0.57 murata-erie 2.0 smallest size do1608-103 10 m h 0.16 coilcraft 3.0 cd43-100 10 m h 0.18 sumida 3.2 cd54-100 10 m h 0.10 sumida 4.5 best efficiency ctx32ct-100 10 m h 0.50 coiltronics 2.2 1210 footprint capacitors for single cell applications, a 10 m f ceramic output capaci- tor is generally all that is required. ripple voltage in burst mode can be reduced by increasing output capacitance. for 2- and 3-cell applications, more than 10 m f is needed. for a typical 2-cell to 5v application, a 47 m f to 100 m f low esr tantalum capacitor works well. avx tps series (100% surge tested) or sprague (dont be vagueask for sprague) 594d series are both good choices for low esr capacitors. alternatively, a 10 m f ceramic in parallel with a low cost (read high esr) electrolytic capacitor, either tantalum or aluminum, can be used instead. for through hole applica- figure 12. recommended component placement. traces carrying high current are direct. trace area at fb pin and v c pin is kept low. lead length to battery should be kept short operation from a laboratory power supply if a lab supply is used, the leads used to connect the circuit to the supply can have significant inductance at the lt1307s switching frequency. as in the previous situa- tion, an electrolytic capacitor may be required at the circuit in order to reduce the ac impedance of the input suffi- ciently. an alternative solution would be to attach the circuit directly to the power supply at the supply terminals, without the use of leads. the power supplys output capacitance will then provide the bulk capacitance the lt1307 circuit requires. aa cell 1 2 3 4 8 7 6 5 r1 r2 l c in d lt1307 keep traces or leads short! v out c out c c ground 1307 f12 r c applicatio s i for atio wu uu
13 lt1307/lt1307b 1307fa tions where small size is not critical, panasonic hfq series aluminum electrolytic capacitors have been found to per- form well. table 2. vendor telephone numbers vendor components telephone coilcraft inductors (708) 639-6400 marcon capacitors (708) 913-9980 murata-erie inductors, capacitors (404) 436-1300 sumida inductors (847) 956-0666 tokin capacitors (408) 432-8020 avx capacitors (207) 282-5111 sprague capacitors (603) 224-1961 coiltronics inductors (407) 241-7876 diodes most of the application circuits on this data sheet specify the motorola mbr0520l surface mount schottky diode. this 0.5a, low drop diode complements the lt1307 quite well. in lower current applications, a 1n4148 can be used, although efficiency will suffer due to the higher forward drop. this effect is particularly noticeable at low output voltages. for higher voltage output applications, such as lcd bias generators, the extra drop is a small percentage of the output voltage so the efficiency penalty is small. the low cost of the 1n4148 makes it attractive wherever it can be used. in through hole applications the 1n5818 is the all around best choice. shutdown pin the lt1307 has a shutdown pin (shdn) that must be grounded to shut the device down or tied to a voltage equal or greater than v in to operate. the shutdown circuit is shown in figure 13. note that allowing shdn to float turns on both the start- up current (q2) and the shutdown current (q3) for v in > 2v be . the lt1307 doesnt know what to do in this situation and behaves erratically. shdn voltage above v in is al- lowed. this merely reverse-biases q3s base emitter junc- tion, a benign condition. figure 13. shutdown circuit v in q3 shutdown current r2 400k 200k q2 1307 f13 q1 start-up current shdn low-battery detector the lt1307s low-battery detector is a simple pnp input gain stage with an open collector npn output. the nega- tive input of the gain stage is tied internally to a 200mv 5% reference. the positive input is the lbi pin. arrange- ment as a low-battery detector is straightforward. figure 14 details hookup. r1 and r2 need only be low enough in value so that the bias current of the lbi pin doesnt cause large errors. for r2, 100k is adequate. the 200mv refer- ence can also be accessed as shown in figure 15. lbo lbi to processor r1 1m r2 100k v in lt1307 1307 f14 3.3v gnd 200mv internal reference + r1 = v lb ?200mv 2 m a figure 14. setting low-battery detector trip point v in lt1307 lbi lbo 200k 10 m f gnd 10k 1307 f15 2n3906 v ref 200mv + figure 15. accessing 200mv reference applicatio s i for atio wu uu
14 lt1307/lt1307b 1307fa reverse battery considerations the lt1307 is built on a junction-isolated bipolar process. the p-type substrate is connected to the gnd pin of the lt1307. substrate diodes, normally reverse-biased, are present on the sw pin and the v in pin as shown in figure 16. when the battery polarity is reversed, these diodes conduct, as illustrated in figure 17. with a single aa or aaa cell, several hundred milliamperes flow in the circuit. the lt1307 can withstand this current without damage. in laboratory tests, the lt1307 performed without degrada- tion after sustaining polarity reversal for the life of a single aa alkaline cell. when using a 2- or 3-cell supply, an external protection diode is recommended as shown in figure 18. when the battery polarity is reversed, the 1n4001 conducts, limiting reverse voltage across the lt1307 to a single diode drop. this arrangement will quickly deplete the cells energy, but it does prevent the lt1307 from excessive power dissipa- tion and potential damage. figure 18. 1n4001 diode protects lt1307 from excessive power dissipation when a 2- or 3-cell battery is used v in sw lt1307 1n4001 1307 f18 2 or 3 cells gnd v in lt1307 1307 f16 gnd 1 cell 1.5v d2 sw d1 q1 figure 16. lt1307 showing internal substrate diodes d1 and d2. in normal operation diodes are reverse-biased v in lt1307 current flow 1307 f17 gnd 1 cell 1.5v d2 sw d1 q1 figure 17. when cell is reversed current flows through d1 and d2 applicatio s i for atio wu uu
15 lt1307/lt1307b 1307fa externally controlled burst mode operation this circuit overcomes the limitation of load-based transitioning between burst mode operation and constant switching mode by adding external control. if m1s gate is grounded by an external open-drain signal, the converter functions normally in constant switching mode, delivering 3.3v. output noise is low, however efficiency at loads less than 1ma is poor due to the 1ma supply current of the lt1307b. if m1s gate is allowed to float, the low-battery detector now drives the v c pin. r3 and r2 set the output to 3v by allowing m1s gate to go to v out until the output voltage drops below 3v. r1 adds hysteresis, resulting in low-frequency burst mode operation ripple voltage at the output. by pulling the v c pin below a v be , quiescent current of the lt1307b drops to 60 m a, resulting in accept- able efficiency at loads in the 100 m a range. v in v c sw fb lbo lbi lt1307b l1 10 m h mbr0520 100k 2 cells 1nf 1 m f ceramic 1307 f19 gnd shdn c2* 10 f ceramic r3 698k r4 1m r2 49.9k r5 590k r1 10m c1 100 f v out 3.3v 200ma 300k v out m1 2n7002 ground = high power/low noise float = burst mode operation shutdown 3.0v in low-power burst mode operation c1 = avx tpsc107k006r0150 l1 = coilcraft do1608-103 sumida cd43-100 c2 optional: reduces output ripple caused by c1's esr * + 0.2s/div 1307 f20 this photo details output voltage as the circuit is switched between the two modes. load current is 100 m a in burst mode operation; 10ma in constant switching mode. this photo shows transient response in constant switch- ing mode with a 10ma to 100ma stepped load. output ripple at the switching frequency can be reduced consid- erably by adding a 10 m f ceramic capacitor in parallel with the 100 m f tantalum. 10ma 100 m a i l v out 500mv/div 2ms/div 1307 f21 v out 100mv/div 100ma 10ma i l typical applicatio s u
16 lt1307/lt1307b 1307fa constant current nicd battery charger with overvoltage protection for acknowledge-back pagers step-up/step-down converter low cost 2-cell to 5v v in v c sw fb lt1307 l1 10 h l1* mbr0520 v in 2.1v to 4.8v 100k 3 cells 608k 1.02m 3.3v 100ma 1000pf l1: coiltronics ctx10-1 or 2 murata erie lqh3c100 efficiency ? 70% to 73% 1307 ta03 1 m f ceramic 2.2 m f ceramic gnd shdn shdn 10 m f ceramic v in v c sw fb lbo lbi lt1307 l1 10 m h v in 1.8v to 1v mbr0520l 47k 1 cell aa or aaa 2200pf 1 m f 2 3 l1: coiltronics ctx10-1 1307 ta04 1nf 3v 200mv 15ma ?00mv 3 cells nicd 2.2 m f ceramic gnd shdn 1 = charge 0 = shutdown 323k 280k 6.7 w 1m overvoltage protection 1 m f ceramic 1 4 30k v in sw fb lt1307 v in 1.4v to 3.3v l1 10 m h 1n5818 shdn 100k 323k 1m 5v 100ma 4700pf c1, c2: panasonic eca0jfq221 (digi-key p5604-nd) l1: sumida cd43-100 1307 ta02 c1* 220 m f 6.3v 0.1 m f gnd 0.1 m f c2 220 m f 6.3v + + typical applicatio s u
17 lt1307/lt1307b 1307fa single cell powered constant current led driver c1 1 m f ceramic l1 10 m h d1 v in 1307 ta05 nc d2 40ma r1 5.1 w 100k on/off v in r2 22k 100k c2 1 m f ceramic q1 2n3906 aa cell c3 22 m f l1: murata-erie lqh3c100k04 d1: 1n4148 c1, c2: ceramic d2, d3: lumex ssl-x100133src/4 "mega-brite" red led or panasonic lng992cf9 high brightness blue led + v in sw fb lt1307b lbi lbo shdn v c gnd flash memory vpp supply v in sw fb lt1307 l1 10 m h d1 47k 232k 1% 2m 1% 1307 ta09 0.33 m f ceramic 2 12v/30ma from 3v 12v/60ma from 5v ~250mv p-p ripple 0.33 m f v c gnd shdn shutdown d1: motorola mbr0520l l1: murata-erie lqh3c100k04 1 m f tantalum 2000pf 1n4148 v in 3v to 5.5v 10pf + high voltage flyback converter v in v in 1v to 5v sw 1n4148 4 6 3 1 lt1307 fb shdn shutdown v c 100k 1000pf gnd r2 240k 1% r1 2v out v out 0.1 m f 1 m f ceramic 0.01 m f 0.1 m f 1307 ta06 optional doubler t1 1:12 t1: dale lpe3325-a190, n = 12 (605) 665-9301 maximum duty cycle: ? 80% for flyback, v out = n(v in ?v sw ) v out = 1.22v 1 + () r1 r2 dc 1 ?dc for 1v in , maximum v out = for 2v in , maximum v out ? 85v. higher voltages achieved with capacitive doubler or tripler no snubber required with specified transformer and v in < 5v 12(1 ?0.2) ? 37v 0.8 1 ?0.8 typical applicatio s u
18 lt1307/lt1307b 1307fa single cell ccfl power supply v in v c d1 100 w 43 ccfl 2 1.5v 5 t1 1 1307 ta08 610 sw fb 0.1 m f c1 0.1 m f 1 cell 1.5v 1.5v 1k l1 33 m h lt1307b 1 = operate 0 = shutdown c1: wima mkp-20 d1: motorola mbr0520l l1: sumida cd54-330 t1: coiltronics ctx110611 q1, q2: zetex fzt-849 gnd shdn 10k dimming 0.1 m f 1n4148 1n4148 1 m f ceramic 10k 47pf 3kv q1 q2 typical applicatio s u u package descriptio ms8 package 8-lead plastic msop (reference ltc dwg # 05-08-1660) msop (ms8) 1001 0.53 0.015 (.021 .006) seating plane note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 0.18 (.077) 0.254 (.010) 1.10 (.043) max 0.22 ?0.38 (.009 ?.015) 0.13 0.05 (.005 .002) 0.86 (.34) ref 0.65 (.0256) bcs 0 ?6 typ detail ? detail ? gauge plane 12 3 4 4.88 0.1 (.192 .004) 8 7 6 5 3.00 0.102 (.118 .004) (note 3) 3.00 0.102 (.118 .004) note 4 0.52 (.206) ref 5.23 (.206) min 3.2 ?3.45 (.126 ?.136) 0.889 0.127 (.035 .005) recommended solder pad layout 0.42 0.04 (.0165 .0015) typ 0.65 (.0256) bsc
19 lt1307/lt1307b 1307fa package descriptio n u information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. n8 package 8-lead pdip (narrow .300 inch) (reference ltc dwg # 05-08-1510) s8 package 8-lead plastic small outline (narrow .150 inch) (reference ltc dwg # 05-08-1610) n8 1098 0.100 (2.54) bsc 0.065 (1.651) typ 0.045 ?0.065 (1.143 ?1.651) 0.130 0.005 (3.302 0.127) 0.020 (0.508) min 0.018 0.003 (0.457 0.076) 0.125 (3.175) min 12 3 4 87 6 5 0.255 0.015* (6.477 0.381) 0.400* (10.160) max 0.009 ?0.015 (0.229 ?0.381) 0.300 ?0.325 (7.620 ?8.255) 0.325 +0.035 0.015 +0.889 0.381 8.255 () *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed 0.010 inch (0.254mm) 0.016 ?0.050 (0.406 ?1.270) 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) so8 1298 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) typ 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) bsc 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 8 7 6 5 0.189 ?0.197* (4.801 ?5.004) 0.228 ?0.244 (5.791 ?6.197) dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * **
20 lt1307/lt1307b 1307fa ? linear technology corporation 1995 lcd bias generator lt/tp 1101 1.5k rev a ? printed in usa part number description comments ltc ? 1163 triple high side driver for 2-cell inputs 1.8v minimum input, drives n-channel mosfets ltc1174 micropower step-down dc/dc converter 94% efficiency, 130 m a i q , 9v to 5v at 300ma lt1302 high output current micropower dc/dc converter 5v/600ma from 2v, 2a internal switch, 200 m a i q lt1304 2-cell micropower dc/dc converter low-battery detector active in shutdown ltc1440/1/2 ultralow power single/dual comparators with reference 2.8 m a i q , adjustable hysteresis ltc1516 2-cell to 5v regulated charge pump 12 m a i q , no inductors, 5v at 50ma from 3v input ltc3400 600ma, 1.2mhz, synchronous boost converter 92% efficiency, v in : 0.85v to 5v, thinsot tm package ltc3401 1a, 3mhz, synchronous boost converter 97% efficiency, v in : 0.5v to 5v, 10-lead msop ltc3402 2a, 3mhz, synchronous boost converter 97% efficiency, v in : 0.5v to 5v, 10-lead msop thinsot is a trademark of linear technology corporation. related parts v in v c sw fb lt1307 l1 d3 d2 d1 100k 1, 2 or 3 cells 1m 100k pwm in 3.3v, 0% to 100% 215k 3.3m v out 16v to 24v 5ma from 1 cell 15ma from 2 cells 35ma from 3 cells ? out 4700pf 10pf l1: 3.3 m h (1 cell) 4.7 m h (2 cells) 10 m h (3 cells) sumida cd43 murata-erie lqh3c coilcraft d01608 c1: 1 m f for +output 0.01 m f for output d1 to d3: mbr0530 or 1n4148 1307 ta07 1 m f 3.3 m f 0.1 m f gnd shdn shutdown c1 1 m f + u typical applicatio linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear.com

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