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for pricing, delivery , and ordering information, please contact maxim/dallas direct! a t 1-888-629-4642 , or visit maxim? website at www.maxim-ic.com. general description the max774/max775/max776 inverting switching regulators deliver high efficiency over three decades of load current. a unique current-limited, pulse- frequency modulated (pfm) control scheme provides the benefits of pulse-width modulation (high efficiency with heavy loads), while using less than 100 a of supply current (vs. 2ma to 10ma for pwm converters). the result is high efficiency over a wide range of loads. these ics also use tiny external components; their high switching frequency (up to 300khz) allows for less than 5mm diameter surface-mount magnetics. the max774/max775/max776 accept input voltages from 3v to 16.5v, and have preset output voltages of -5v, -12v, and -15v, respectively. or, the output voltage can be user-adjusted with two resistors. maximum v in - v out differential voltage is limited only by the break- down voltage of the chosen external switch transistor. these inverters use external p-channel mosfet switches, allowing them to power loads up to 5w. if less power is required, use the max764/max765/max766 inverting switching regulators with on-board mosfets. applications lcd-bias generators high-efficiency dc-to-dc converters battery-powered applications data communicators features 85% efficiency for 5ma to 1a load currents up to 5w output power 100? (max) supply current 5? (max) shutdown current 3v to 16.5v input range -5v (max774), -12v (max775), -15v (max776), or adjustable output voltage current-limited pfm control scheme 300khz switching frequency ordering information * contact factory for dice specifications. max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers ________________________________________________________________ maxim integrated products 1 1 2 3 4 5 8 7 6 max774 max775 max776 dip/so top view gnd ext cs v+ out fb shdn ref pin configuration max774 output -5v ref shdn gnd v+ cs ext out on/off input 3v to 16v p fb typical operating circuit part temp range pin-package max774 cpa 0? to +70? 8 plastic dip max774csa 0? to +70? 8 so max774c/d 0? to +70? dice* max774epa -40? to +85? 8 plastic dip max774esa -40? to +85? 8 so max774mja -55? to +125? 8 cerdip 19-0191; rev 2; 12/02 evaluation kit available ordering information continued on last page.
max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers 2 _______________________________________________________________________________________ absolute maximum ratings supply voltages v+ to out ...........................................................................21v v+ to gnd ..............................................................-0.3v, +17v out to gnd ........................................................-0.3v, to -17v ref, shdn, fb, cs...................................-0.3v to (v+ + 0.3v) ext ...............................................(v out - 0.3v) to (v+ + 0.3v) continuous power dissipation (t a = +70?) plastic dip (derate 9.09mw/? above +70?) .............727mw so (derate 5.88mw/? above +70?) ..........................471mw cerdip (derate 8.00mw/? above +70?) ..................640mw operating temperature ranges: max77_c_ _ .........................................................0? to +70? max77_e_ _ ......................................................-40? to +85? max77_mja ...................................................-55? to +125? maximum junction temperatures: max77_c_ _/e_ _ ...........................................................+150? max77_mja..................................................................+175? storage temperature range .............................-65? to +160? lead temperature (soldering, 10s) .................................+300? electrical characteristics (v+ = 5v, i load = 0ma, c ref = 0.1?, t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. parameter symbol conditions output voltage line regulation (circuit of figure 2 bootstrapped) min typ max units v+ input voltage range v+ 3.0 16.5 v supply current v+ = 16.5v, shdn 0.4v (operating) max774, 4v v+ 15v, i load = 0.5a 100 ? 0.035 mv/v v+ = 10v, shdn 1.6v (shutdown) 25 max776, 4v v+ 6v, i load = 0.1a 0.137 v+ = 16.5v, shdn 1.6v (shutdown) 4 fb trip point 3v v+ 16.5v -10 10 mv fb input current i fb max77_c max775, 4v v+ 8v, i load = 0.2a ?0 na 0.088 max77_e ?0 max775, 0ma i load 500ma, v+ = 5v 1.5 max77_m ?0 output voltage load regulation (circuit of figure 2 bootstrapped) output voltage v out max774 -4.80 -5 -5.20 v max774, 0a i load 1a, v+ = 5v 1.5 max775 mv/a -11.52 -12 -12.48 max776, 0ma i load 400ma, v+ = 5v max776 1.0 -14.40 -15 -15.60 reference voltage v ref i ref = 0? max77_c 1.4700 1.5 1.5300 v max77_e 1.4625 1.5 1.5375 max77_m 1.4550 1.5 1.5450 ref load regulation 0? i ref 100? max77_c/e 410 mv max77_m 415 ref line regulation 3v v+ 16.5v 40 100 ?/v
max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers _______________________________________________________________________________________ 3 electrical characteristics (continued) (v+ = 5v, i load = 0ma, c ref = 0.1?, t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) 3v v+ 16.5v v+ = 16.5v, shdn = 0v or v+ max774, v+ = 5v, i load = 1a max776, v+ = 5v, i load = 400ma max775, v+ = 5v, i load = 500ma conditions v 1.6 v ih shdn input voltage high ? ? shdn input current % 82 efficiency (circuit of figure 2 bootstrapped) 87 c ext = 1nf, v+ = 12v c ext = 1nf, v+ = 12v ns 50 v+ = 12v v+ = 12v ext fall time ? 88 ns 1.8 2.3 2.8 t off (max) switch minimum off-time ? 12 16 20 t on (max) switch maximum on-time ? ? cs input current 50 units min typ max symbol ext rise time parameter 160 210 260 3v v+ 16.5v mv 180 210 240 v cs current-limit trip level (v+ ?cs) 0.3 3v v+ 16.5v v 0.4 v il shdn input voltage low max77_m max77_c/e max77_m max77_c/e
max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers 4 _______________________________________________________________________________________ __________________________________________typical operating characteristics (t a = +25?, unless otherwise noted.) 90 1 10 1000 max774 efficiency vs. load current v out = -5v (bootstrapped) 70 80 max1774/5/6-01a load current (ma) efficiency (%) 60 50 100 v in = 5v v in = 3v v in = 15v 90 50 1 100 max774 efficiency vs. load current v out = -5v (nonbootstrapped) 60 80 ma774/5/6--1b load current (ma) efficiency (%) 10 1000 70 v in = 15v v in = 5v v in = 4v 90 50 -40 -20 40 100 max774 efficiency vs. temperature 60 80 max774/5/6-2 temperature (?) efficiency (%) 20 06080 70 i load = 600ma i load = 1a i load = 100ma v in = 5v bootstrapped 90 50 1 100 max776 efficiency vs. load current v out = -15v (bootstrapped) 60 80 ma774/5/6-1c load current (ma) efficiency (%) 10 1000 70 v in = 4v v in = 3v v in = 6v v in = 5v 90 50 1 100 max774/max775/max776 efficiency vs. load current v out = -24v (nonbootstrapped) 60 80 ma774/5/6--1f load current (ma) efficiency (%) 10 1000 70 v in = 4v v in = 5v v in = 6v 90 50 1 100 max776 efficiency vs. load current v out = -15v (nonbootstrapped) 60 80 ma774/5/6-1d load current (ma) efficiency (%) 10 1000 70 v in = 4v v in = 5v v in = 15v v in = 6v 90 50 1 100 max775 efficiency vs. output current v out = -12v (bootstrapped) 60 80 ma774/5/6--1 e output current (ma) efficiency (%) 10 1000 70 v in = 4v v in = 5v v in = 8v 90 50 1 100 max774/max775/max776 efficiency vs. load current v out = -24v output (zener connection) 60 80 ma774/5/6--1g load current (ma) efficiency (%) 10 1000 70 v in = 4v v in = 5v v in = 6v 88 74 2 4 10 16 max774 efficiency vs. input voltage v out = -5v at 100ma 78 76 84 86 max774/5/6-3 input voltage (v) efficiency (%) 8 61214 82 80 bootstrapped nonbootstrapped v out = -5v at 100ma
max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers _______________________________________________________________________________________ 5 _____________________________typical operating characteristics (continued) (t a = +25?, unless otherwise noted.) 2.5 1.5 -60 60 switch off-time vs. temperature 2.0 max761-13 temperature ( c) t off (s) 0 120 v+ = 5v 5.0 2.5 100 startup voltage vs. load current (bootstrapped) 3.0 4.5 ma744/5/6-14 load current (ma) start-up voltage (v) 10 1000 3.5 1 4.0 v out = -12v v out = -15v v out = -5v 5.0 2.5 0.1 100 startup voltage vs. load current (nonbootstrapped) 3.0 4.5 ma744/5/6-15 load current (ma) start-up voltage (v) 10 1000 3.5 1 4.0 v out = -24v v out = -15v v out = -12v v out = -5v 2200 800 2 4 10 16 max774 maximum load vs. input voltage 1200 1000 1800 2000 max774/5/6-16 input voltage (v) load current (ma) 8 61214 1600 1400 bootstrapped nonbootstrapped v out = -5v 20 -60 -40 60 140 ext rise and fall times vs. temperature 40 30 max774/5/6-9 temperature ( c) t rise & t fall (ns) 40 20 0 -20 80 120 100 50 5v rise 60 80 70 90 100 120 110 130 5v fall 12v rise 12v fall c ext = 1nf -60 -40 60 140 ext rise and fall times vs. temperature max774/5/6-10 temperature ( c) t rise & t fall (ns) 40 20 0 -20 80 120 100 5v rise 450 400 500 5v fall 12v rise 12v fall c ext = 5nf 300 250 350 150 100 200 50 17 15 -60 60 switch on-time vs. temperature 16 max761-13 temperature ( c) t on (s) 0 120 v+ = 5v 8.0 7.8 7.6 7.4 7.2 7.0 6.8 6.6 6.4 6.2 6.0 -60 -40 60 140 switch on-time/off-time ratio max774/5/6-6 temperature ( c) t on /t off ratio (s/s) 40 20 0 -20 80 120 100 v+ = 5v 4.0 0 -60 -40 60 140 shutdown current vs. temperature 1.0 0.5 2.5 3.5 max774/5/6-7 temperature ( c) i cc (a) 40 20 0 -20 80 120 100 2.0 1.5 3.0 v+ = 15v v+ = 8v v+ = 4v
max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers 6 _______________________________________________________________________________________ 80 66 -60 -40 60 140 operating supply current vs. temperature 70 68 76 78 max774/5/6-8 temperature ( c) i cc (a) 40 20 0 -20 80 120 100 74 72 v+ = 16.5v v+ = 10v v+ = 3v 1.506 1.492 -60 -40 60 140 reference temperature coefficient 1.496 1.494 1.502 1.504 max774/5/6-12 temperature ( c) reference output (v) 40 20 0 -20 80 120 100 1.500 1.498 235 230 225 220 215 210 205 200 195 190 185 -60 -40 60 140 cs trip level max774/5/6-11 temperature ( c) cs trip level (mv) 40 20 0 -20 80 120 100 250 200 150 100 50 0 -60 -40 60 140 reference output resistance max774/5/6-13 temperature ( c) reference output resistance ( ? ) 40 20 0 -20 80 120 100 i ref = 50a i ref = 100a i ref = 10a _____________________________typical operating characteristics (continued) (t a = +25?, unless otherwise noted.)
max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers _______________________________________________________________________________________ 7 __________________________________________typical operating characteristics (t a = +25?, unless otherwise noted.) circuit of figure 2 v+ = 6.5v, i load = 1a, v out = -5v a: output ripple, 200mv/div b: ext waveform, 10v/div c: inductor current, 2a/div operating waveforms 10 s/div a b c circuit of figure 2 v out = -5v, v+ = 4.7v i load = 1.05a (1a/div) inductor current near full load 20 s/div 1a/div 0a circuit of figure 2 i load = 300ma, v out = -5v v+ = 8v, l = 22 h continuous conduction at one-half current limit 20 s/div 1a/div 0a circuit of figure 2 v+ = 6v, i load = 1a, v out = -5v a: shutdown pulse, 0v to v+, 5v/div b: v out , 2v/div entry/exit from shutdown 2ms/div a b
max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers 8 _______________________________________________________________________________________ ______________________________________________________________pin description pin name function 1 out 2 fb 3 shdn 4 ref 1.5v reference output that can source 100?. bypass to ground with 0.1?. 5 v+ positive power-supply input 6 cs noninverting input to the current-sense comparator. typical trip level is 210mv (relative to v+). 7 ext the gate-drive output for an external p-channel power mosfet. ext swings from out to v+. 8 gnd ground the sense input for fixed-output operation (v fb = v ref ). out is connected to the internal voltage divider, and it is the negative supply input for the ext driver. feedback input. when v fb = v ref , the output will be the factory preset value. for adjustable operation, use an external voltage divider, as described in the adjustable output section. active-high shutdown input. with shdn high, the part is in shutdown mode and the supply current is less than 5?. connect to gnd for normal operation. typical operating characteristics (continued) (t a = +25?, unless otherwise noted.) circuit of figure 2 v+ = 6v, v out = -5v a: i load , 30ma to 1a, 1a/div b: v out , 100mv/div, ac-coupled load-transient response 100 s/div a b circuit of figure 2 v out = -5v, i load = 1a a: v+, 3v to 8v, 5v/div b: v out , 100mv/div, ac-coupled line-transient response 2ms/div a b
detailed description the max774/max775/max776 are negative-output, inverting power controllers that can be configured to drive an external p-channel mosfet. the output voltages are preset to -5v (max774), -12v (max775), or -15v (max776). additionally, all three parts can be set to any desired output voltage using an external resistor divider. the max774/max775/max776 have a unique control scheme (figure 1) that combines the advantage of pulse-skipping, pulse-frequency-modulation (pfm) converters (ultra-low supply current) with the advan- tage of pulse-width modulation (pwm) converters (high efficiency with heavy loads). this control scheme allows the devices to achieve 85% efficiency with loads from 5ma to 1a. as with traditional pfm converters, the external p-channel mosfet power transistor is turned on when the voltage comparator senses that the output is below the reference voltage. however, unlike traditional pfm converters, switching is controlled by the combination of a switch current limit (210mv/r sense ) and on-time/off-time limits set by one-shots. once turned on, the mosfet stays on until the 16? maximum on- time limit is reached or the switch current reaches its limit (as set by the current-sense resistor). once off, the switch is typically held off for a minimum of 2.3?. it will stay off until the output drops below the level determined by v ref and the feedback divider network. with light loads, the mosfet switches on for one or more cycles and then switches off, much like in tradi- tional pfm converters. to increase light-load efficiency, max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers _______________________________________________________________________________________ 9 n 1.5v reference q trig one-shot q trig one-shot current- control circuits mode comparator error comparator current comparator from v+ from out 0.2v (full current) 0.1v (half current) from v+ max774 max775 max776 ref v+ shdn fb out cs ext gnd s r q 50mv figure 1. functional diagram
max774/max775/max776 the current limit for the first two pulses is set to one-half the peak current limit. if those pulses bring the output voltage into regulation, the voltage comparator keeps the mosfet off, and the current limit remains at one-half the peak current limit. if the output voltage is out of regulation after two consecutive pulses, the current limit for the next pulse will equal the full current limit. with heavy loads, the mosfet first switches twice at one-half the peak current value. subsequently, it stays on until the switch current reaches the full current limit, and then turns off. after it is off for 2.3?, the mosfet switches on once more, and remains on until the switch current again reaches its limit. this cycle repeats until the output is in regulation. a benefit of this control scheme is that it is highly effi- cient over a wide range of input/output ratios and load currents. additionally, pfm converters do not operate with constant-frequency switching, and have relaxed stability criterion (unlike pwm converters). as a result, their external components require smaller values. with pfm converters, the output voltage ripple is not concentrated at the oscillator frequency (as it is with pwm converters). for applications where the ripple fre- quency is important, the pwm control scheme must be used. however, for many other applications, the smaller capacitors and lower supply current of the pfm control scheme make it the better choice. the output voltage ripple with the max774/max775/max776 can be held quite low. for example, using the circuit of figure 2, only 100mv of output ripple is produced when generat- ing a -5v at 1a output from a +5v input. bootstrapped vs. nonbootstrapped operation figures 2 and 3 are the standard application circuits for bootstrapped mode, and figure 4 is the circuit for nonbootstrapped mode. since ext is powered by out, using bootstrapped or nonbootstrapped mode will directly affect the gate drive to the fet. ext swings from v+ to v out . in bootstrapped operation, out is -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers 10 ______________________________________________________________________________________ max774 max775 max776 out v+ shdn cs fb ext gnd p 7 8 c2 0.1 f r1 0.07 ? c1 150 f 6 5 2 3 1 ref 4 q1 si9435 1n5822/ mbr340 l1 22 h c4 * v in c3 0.1 f v out * max774 = 330 f, 10v max775, max776 = 120 f, 20v product max774 max775 max776 output voltage (v) -5 -12 -15 input voltage (v) 3 to 15 3 to 8 3 to 5 output current (a) 1 0.5 0.4 note: si9435 has v gs of 20v max max774 max775 max776 out v+ shdn cs fb ext gnd p 7 8 r2 r3 0.07 ? c1 150 f 6 5 2 3 1 ref 4 q1 si9435 1n5822/ mbr340 l1 22 h c4 * v in c3 0.1 f v out c2 0.1 f r1 * max774 = 330 f, 10v max775, max776 = 120 f, 20v figure 2. bootstrapped connection using fixed output voltages figure 3. bootstrapped connection using external feedback resistors figure 4. nonbootstrapped operation (v in > 4.5v) max774 max775 max776 out v+ shdn cs fb ext gnd p 7 8 r2 r3 0.07 ? c1 150 f 6 5 2 3 1 ref 4 q1 si9435 1n5822/ mbr340 l1 22 h c4 * v in c3 0.1 f v out c2 0.1 f r1 * max774 = 330 f, 10v max775, max776 = 120 f, 20v
connected to the output voltage (-5v, -12v, -15v). in nonbootstrapped operation, out is connected to ground, and ext now swings from v+ to ground. at high input-to-output differentials, it may be neces- sary to use nonbootstrapped mode to avoid the 21v v+ to v out maximum rating. also, observe the v gs maxi- mum rating of the external transistor. at intermediate voltages and currents, the advantages of bootstrapped vs. nonbootstrapped operation are slight. when input voltages are less than about 4v, always use the boot- strapped circuit. shutdown and quiescent current the max774/max775/max776 are designed to save power in battery-powered applications. a ttl/cmos logic-level shutdown input (shdn) has been provided for the lowest-power applications. when shut down (shdn = v+), most internal bias current sources and the reference are turned off so that less than 5? of current is drawn. in normal operation, the quiescent current will be less than 100?. however, this current is measured by forc- ing the external switch transistor off. even with no load, in an actual application, additional current will be drawn to supply the feedback resistors?and the diode? and capacitor? leakage current. under no-load condi- tions, you should see a short current pulse at half the peak current approximately every 100ms (the exact period depends on actual circuit leakages). ext drive voltages ext swings from out to v+ and provides the drive out- put for an external power mosfet. when using the on- chip feedback resistors for the preset output voltages, the voltage at out equals the output voltage. when using external feedback resistors, out may be tied to gnd or some other potential between v out and gnd. always observe the v+ to out absolute maximum rat- ing of 21v. for v+ to output differentials greater than 21v, out must be tied to a potential more positive than the output and, therefore, the output voltage must be set with an external resistor divider. in nonbootstrapped operation with low input voltages (<4v), tie out to a negative voltage to fully enhance the external mosfet. accomplish this by creating an inter- mediate voltage for v out with a zener diode (figure 5). __________________design procedure setting the output voltage the max774/max775/max776 are preset for -5v, -12v, and -15v output voltages, respectively; however, they may also be adjusted to other values with an external voltage divider. for the preset output voltage, connect fb to ref and connect out to the output (figure 3). in this case, the output voltage is sensed by out. for an adjustable output (figures 3 and 4), connect an external resistor divider from the output voltage to fb, and from fb to ref. in this case, the divided-down out- put voltage is sensed via the fb pin. there are three reasons to use the external resistor divider: 1) an output voltage other than a preset value is desired. 2) the input-to-output differential exceeds 21v. 3) the output voltage (v out to gnd) exceeds -15v. see figures 3 and 4 for adjustable operation. the impedance of the feedback network should be low enough that the input bias current of fb is not a factor. for best efficiency and precision, allow 10? to flow through the network. calculate (v ref -v fb ) / r1 = 10?. since v ref = 1.5v and v fb = 0v, r1 becomes 150k ? . then calculate r2 as follows: r2 v out ___ = _______ r1 v ref (or, v out = 10 a) ______ r2 choosing an inductor practical inductor values range from 10? to 50?. the maximum inductor value is not particularly critical. for highest current at high ? v out ? to v+ ratios, the max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers ______________________________________________________________________________________ 11 figure 5. connection using zener diode to boost base drive r1 max774 max775 max776 out gnd fb r2 8 2 1 ref 4 0.1 f 0.1 f v out r z 6v v z + v in 10v ? vout ? v z > i z r z i z = zener breakdown current v z = zener breakdown voltage v in = input supply voltage
max774/max775/max776 inductor should not be so large that the peak current never reaches the current limit. that is: [ v+(min) - v sw (max) ] x 12? l(max) _______________________________ i lim (max) this is only important if v in 1t off (min) ? _______ ? < ? = ___________ v out 6t on (max) more important is that the inductor not be so small that the current rises much faster than the current-limit comparator can respond. this would be wasteful and reduce efficiency. calculate the mini mum inductor value as follows: [ v+(max) - v sw (min) ] x 0.3? l(min) _______________________________ (i) x i lim (min) where l is in ?, 0.3? is an ample time for the com- parator response, i lim is the current limit (see the current-sense resistor section), and (i) is the allow- able percentage of overshoot. as an example, figure 2's circuit uses a 3a peak current. if we allow a 15% overshoot and 15v is the maximum input voltage, then l(min) is 16?. the actual value of l above this limit has minimal effect on this circuit's operation. for highest efficiency, use a coil with low dc resistance. coils with 30m ? or lower resistance are available. to min- imize radiated noise, use a torroid, pot-core, or shielded- bobbin inductor. inductors with a ferrite core or equivalent are recommended. make sure that the inductor? satura- tion current rating is greater than i lim (max). diode selection the ics?high switching frequencies demand a high- speed rectifier. schottky diodes such as the 1n5817 to 1n5822 families are recommended. choose a diode with an average current rating approximately equal to or greater than i lim (max) and a voltage rating higher than v in (max) + v out . for high-temperature applica- tions, schottky diodes may be inadequate due to their high leakage currents; instead, high-speed silicon diodes may be used. at heavy loads and high tempera- ture, the benefits of a schottky diode? low forward volt- age may outweigh the disadvantages of its high leak- age current. current-sense resistor the current-sense resistor limits the peak switch cur- rent to 210mv/r sense , where r sense is the value of the current-sense resistor, and 210mv is the current- sense comparator threshold (see current-limit trip level in the electrical characteristics ). to maximize efficiency and reduce the size and cost of external components, minimize the peak current. however, since the output current is a function of the peak current, do not set the limit too low. see figures 6? to determine the sense resistor, as well as the peak current, for the required load current. -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers 12 ______________________________________________________________________________________ maximum output current (ma) input voltage (v) 0 500 1000 1500 2000 2500 34 567 8 9101112 13 14 15 v out = -5v r sense = 0.05 ? r sense = 0.06 ? r sense = 0.08 ? r sense = 0.09 ? r sense = 0.07 ? max775-fig6 figure 6. max774 maximum output current vs. input voltage (v out = -5v) figure 7. max775 maximum output current vs. input voltage (v out = -12v) maximum output current (ma) 0 200 400 600 800 1000 9 input voltage (v) max775-fig07 3456 78 r sense = 0.05 ? r sense = 0.06 ? r sense = 0.07 ? r sense = 0.08 ? r sense = 0.09 ? v out = -12v
to choose the proper current-sense resistor, simply fol- low the two-step procedure outlined below: 1) determine: input voltage range, v+ maximum (absolute) output voltage, v out maximum output current, i load for example, let v+ range from 4v to 6v, and choose v out = -24v and i out = 150ma. 2) next, referring to figure 9, find the curve with the lowest current limit whose output current (with the lowest input voltage) meets your requirements. in our example, a curve where i out is >150ma with a 4v input and a -24v output is optimal. the r sense = 80m ? (figure 9) shows only approxi- mately 125ma of output current with a 4v input, so we look next at the r sense = 70m ? line. it shows i out >150ma for v+ = 4v and v out = -24v. the current limit will be 0.210v / 0.070 ? = 3a. these curves take into account worst-case inductor (?0%) and current- sense trip levels, but not sense-resistor tolerance. the switch on resistance is 70m ? . standard wire-wound and metal-film resistors have an inductance high enough to degrade performance. metal-film resistors are usually deposited on a ceramic rod in a spiral, making their inductances relatively high. surface-mount (or chip) resistors have very little induc- tance and are well suited for use as current-sense resistors. to use through-hole resistors, irc has a wire resistor that is simply a band of metal shaped as a ? so that inductance is less than 10nh (an order of mag- nitude less than metal-film resistors). these are avail- able in resistance values between 5m ? and 0.1 ? . external switching transistor the max774/max775/max776 are capable of driving p-channel enhancement-mode mosfet transistors only. the choice of power transistor is dictated by input and output voltage, peak current rating, on-resistance, gate- source threshold, and gate capacitance. the drain-to- source rating must be greater than the v+ - v out input-to-output voltage differential. the gate-to-source rating must be greater than v+ (the source voltage) plus the absolute value of the most negative swing of ext. for bootstrapped operation, the most negative swing of ext is v out . in nonbootstrapped operation, this may be ground or some other negative voltage. gate capaci- tance is not normally a limiting factor, but values should be less than 1nf for best efficiency. for maximum effi- ciency, the mosfet should have a very-low on-resis- tance at the peak current and be capable of handling that current. the transistor chosen for the typical operat- ing circuit has a 30v drain-source voltage limit and a 0.07 ? drain-source on-resistance at v gs = -10v. table 1 lists suppliers of switching transistors suitable for use with the max774/max775/max776. max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers ______________________________________________________________________________________ 13 figure 8. max776 maximum output current vs. input voltage (v out = -15v) figure 9. max774/max775/max776 maximum output current vs. input voltage (v out = -24v) maximum output current (ma) 100 input voltage (v) max776-fig08 200 300 400 500 600 700 34567 r sense = 0.05 ? r sense = 0.06 ? r sense = 0.07 ? r sense = 0.08 ? r sense = 0.09 ? v out = -15v maximum output current (ma) input voltage (v) 0 34 5678 9101112 13 14 15 max776-fig09 200 400 600 800 r sense = 0.05 ? r sense = 0.06 ? r sense = 0.07 ? r sense = 0.08 ? r sense = 0.09 ? v out = -24v
capacitors choose the output capacitor (c4 of figures 2, 3, and 4) to be consistent with size, ripple, and output voltage requirements. place capacitors in parallel if the size desired is unobtainable. this will not only increase the capacitance, but also decrease the capacitor? esr (a major contributor of ripple). a 330? tantalum output filter capacitor with 0.07 ? esr typically maintains 120mv p-p output ripple when generating -5v at 1a from a 5v input. smaller capacitors are acceptable for lighter loads or in applications that can tolerate higher output ripple. the value of c4 is chosen such that it acquires as small a charge as possible during the switch on-time. the amount of ripple as a function of capacitance is give by: v out x i out x esr i out x t off (min) ? v p-p = _____________________ + _________________ v in c when evaluating this equation, be sure to use the capacitance value at the switching frequency. at 200khz, the 330? tantalum capacitor of figures 2, 3, or 4 may degrade by a factor of ten, which will signifi- cantly alter the ripple voltage calculation. the esr of both the bypass and filter capacitors also affects efficiency. best performance is obtained by doubling up on the filter capacitors or using low-esr capacitors. capacitors must have a ripple current rat- ing equal to the peak current. the smallest low-esr smt capacitors currently avail- able are the sprague 595d series. sanyo os-con organic semiconductor through-hole capacitors also exhibit low esr and are especially effective at low tem- peratures. table 1 lists the phone numbers of these and other manufacturers. pc layout and grounding due to high current levels and fast switching wave- forms, proper pc board layout is essential. use a star ground configuration; connect the ground lead of the input bypass capacitor, the output capacitor, the induc- tor, and the gnd pin of the max774/max775/max776 at a common point very close to the device. addi- tionally, input capacitor c2 (figures 3 and 4) should be placed extremely close to the device. if an external resistor divider is used (figures 3 and 4), the trace from fb to the resistors must be extremely short. max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers 14 ______________________________________________________________________________________ table 1. component suppliers supplier phone fax coiltronics (407) 241-7876 (407) 241-9339 gowanda (716) 532-2234 (716) 532-2702 sumida japan 81-3-3607-5111 81-3-3607-5144 sumida usa (708) 956-0666 (708) 956-0702 kemet (803) 963-6300 (803) 963-6322 matsuo (714) 969-2491 (714) 960-6492 nichicon (708) 843-7500 (708) 843-2798 sanyo japan 81-7-2070-6306 81-7-2070-1174 sanyo usa (619) 661-6835 (619) 661-1055 sprague (603) 224-1961 (603) 224-1430 united chemi-con (714) 255-9500 (714) 255-9400 motorola (800) 521-6274 (602) 952-4190 nihon usa 81-3-3494-7411 81-3-3494-7414 nihon japan (805) 867-2555 (805) 867-2556 harris (407) 724-3729 (407) 724-3937 international rectifier (310) 322-3331 (310) 322-3332 siliconix (408) 988-8000 (408) 970-3950 irc (704) 264-8861 (704) 264-8866 inductors capacitors diodes power mosfets current-sense resistors
max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers ______________________________________________________________________________________ 15 chip topography ordering information (continued) .109" (2.769mm) 0.080 (2.032mm) gnd out ref shdn fb v+ cs ext transistor count: 442; substrate connected to v+. part temp range pin-package max775 cpa 0? to +70? 8 plastic dip max775csa 0? to +70? 8 so max775c/d 0? to +70? dice* max775epa -40? to +85? 8 plastic dip max775esa -40? to +85? 8 so max775mja -55? to +125? 8 cerdip max776 cpa 0? to +70? 8 plastic dip max776csa 0? to +70? 8 so max776c/d 0? to +70? dice* max776epa -40? to +85? 8 plastic dip MAX776ESA -40? to +85? 8 so max776mja -55? to +125? 8 cerdip * contact factory for dice specifications. l dim a a1 b c d e e h h l min 0.053 0.004 0.014 0.007 0.189 0.150 0.228 0.010 0.016 0? max 0.069 0.010 0.019 0.010 0.197 0.157 0.244 0.020 0.050 8? min 1.35 0.10 0.35 0.19 4.80 3.80 5.80 0.25 0.40 0? max 1.75 0.25 0.49 0.25 5.00 4.00 6.20 0.50 1.27 8? inches millimeters 8-pin plastic small-outline package h e d e a a1 c h x 45? 0.127mm 0.004in. b 1.27 bsc 0.050 bsc 21-325a package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .)
maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 16 __________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 (408) 737-7600 2002 maxim integrated products printed usa is a registered trademark of maxim integrated products. max774/max775/max776 -5v/-12v/-15v or adjustable, high-efficiency, low i q inverting dc-to-dc controllers c a a2 e1 d e e a e b a3 b1 b dim a a1 a2 a3 b b1 c d d1 e e1 e e a e b l min 0.015 0.125 0.055 0.016 0.050 0.008 0.348 0.005 0.300 0.240 0.115 0 ? max 0.200 0.175 0.080 0.022 0.065 0.012 0.390 0.035 0.325 0.280 0.400 0.150 15 ? min 0.38 3.18 1.40 0.41 1.27 0.20 8.84 0.13 7.62 6.10 2.92 0 ? max 5.08 4.45 2.03 0.56 1.65 0.30 9.91 0.89 8.26 7.11 10.16 3.81 15 ? inches millimeters 2.54 bsc 7.62 bsc 0.100 bsc 0.300 bsc a1 l d1 e 21-324a 8-pin plastic dual-in-line package c a d b1 b dim a b b1 b2 c d e e1 e l l1 q s s1 min 0.014 0.038 0.023 0.008 0.220 0.290 0.125 0.150 0.015 0.005 0 ? max 0.200 0.023 0.065 0.045 0.015 0.405 0.310 0.320 0.200 0.060 0.055 15 ? min 0.36 0.97 0.58 0.20 5.59 7.37 3.18 3.81 0.38 0.13 0 ? max 5.08 0.58 1.65 1.14 0.38 10.29 7.87 8.13 5.08 1.52 1.40 15 ? inches millimeters q l s1 e 21-326d 8-pin ceramic dual-in-line package s l1 e e1 2.54 bsc 0.100 bsc b2 package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .)

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