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_______________general description the max770?ax773 step-up switching controllers pro- vide 90% efficiency over a 10ma to 1a load. a unique current-limited pulse-frequency-modulation (pfm) control scheme gives these devices the benefits of pulse-width-modulation (pwm) converters (high efficiency at heavy loads), while using less than 110? of supply current (vs. 2ma to 10ma for pwm converters). these ics use tiny external components. their high switching frequencies (up to 300khz) allow surface- mount magnetics of 5mm height and 9mm diameter. the max770/max771/max772 accept input voltages from 2v to 16.5v. output voltages are preset at 5v, (max770), 12v (max771), and 15v (max772); they can also be adjusted using two resistors. the max773 accepts inputs from 3v to 16.5v. for a wider input range, it features an internal shunt regulator that allows unlimited higher input voltages. the max773? out- put can be set to 5v, 12v, or 15v, or it can be adjusted with two resistors. the max770?ax773 drive external n-channel mosfet switches, allowing them to power loads up to 15w. if less power is required, use the max756/max757 or max761/max762 step-up switching regulators with on- board mosfets. ________________________applications palmtops/handy-terminals high-efficiency dc-dc converters battery-powered applications positive lcd-bias generators portable communicators flash memory programmers ____________________________features ? 90% efficiency for 10ma to 1a load currents ? up to 15w output power ? 110? max supply current ? 5? max shutdown current ? 2v to 16.5v input range (max770/max771/max772) ? internal shunt regulator for high input voltages (max773) ? preset or adjustable output voltages max770: 5v or adjustable max771: 12v or adjustable max772: 15v or adjustable max773: 5v, 12v, 15v, or adjustable ? current-limited pfm control scheme ? 300khz switching frequency ______________ordering information ordering information continued at end of data sheet. *contact factory for dice specifications. **contact factory for availability and processing to mil-std-883b. max770?ax773 5v/12v/15v or adjustable, high-efficiency, low i q , step-up dc-dc controllers ________________________________________________________________ maxim integrated products 1 1 2 3 4 8 7 6 5 cs gnd agnd ref shdn fb v+ ext max770 max771 max772 dip/so _________________pin configurations fb agnd gnd v+ cs ext n ref shdn on/off output 12v input 2v to v out max771 __________typical operating circuit part temp. range pin-package max770 cpa 0? to +70? plastic dip max770csa 0? to +70? 8 so max770c/d 0? to +70? dice* max770epa -40? to +85? 8 plastic dip max770esa -40? to +85? 8 so max770mja -55? to +125? 8 cerdip** top view pin configurations continued at end of data sheet. 19-0202; rev 2; 11/96 evaluation kit manual follows data sheet for free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. for small orders, phone 408-737-7600 ext. 3468.
max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 2 _______________________________________________________________________________________ absolute maximum ratings supply voltages v+ to gnd ............................................................. -0.3v to 17v v+ to sgnd ............................................................. -0.3v to 7v sgnd ........................................................ -0.3v to (v+ + 0.3v) ext, cs, ref, lbo, lbi, shdn, fb ............. -0.3v to (v+ + 0.3v) exth, extl .................................................. -0.3v to (v+ + 0.3v) v5, v12, v15 ............................................................. -0.3v to 17v gnd to agnd ......................................................... 0.1v to -0.1v i sgnd .................................................................................. 50ma continuous power dissipation (t a = +70 c) 8-pin plastic dip (derate 9.09mw/ c above +70 c) .... 727mw 8-pin so (derate 5.88mw/ c above +70 c) ................ 471mw 8-pin cerdip (derate 8.00mw/ c above +70 c) ........ 640mw 14-pin plastic dip (derate 10.00mw/ c above +70 c) ............................. 800mw 14-pin so (derate 8.33mw/ c above +70 c) .............. 667mw 14-pin cerdip (derat e 9.09mw/ c above +70 c) ...... 727mw operating temperature ranges max77_c _ _ ........................................................ 0 c to +70 c max77_e _ _ ...................................................... -40 c to +85 c max77_mj_ ................................................... -55 c to +125 c junction temperatures max77_c _ _/e _ _ .......................................................... +150 c max77_mj_ .................................................................. +175 c storage temperature range ............................. -65 c to +160 c lead temperature (soldering, 10sec) ............................. +300 c 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. electrical characteristics (v+ = 5v, i load = 0ma, t a = t min to t max , unless otherwise noted. typical values are at t a = +25 c.) parameter sym bol conditions min typ max units supply current 85 110 m a standby current 2 5 m a 4 output voltage (note 1) v+ = 2.0v to 5.0v, over full load range 4.80 5.0 5.20 v v+ = 2.0v to 12.0v, over full load range 11.52 12.0 12.48 v+ = 2.0v to 15.0v, over full load range 14.40 15.0 15.60 figure 2a, v+ = 2.7v to 4.5v, i load = 700ma, v out = 5v 5 mv/v figure 2a, v+ = 3v, i load = 30ma to 1a, v out = 5v 20 mv/a maximum switch on-time t on (max) 12 16 20 m s minimum switch off-time t off (min) 1.8 2.3 2.8 m s efficiency 87 % reference voltage v ref i ref = 0 m a 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 output voltage line regulation ( note 2) output voltage load regulation (note 2) v+ = 4v, i load = 500ma, v out = 5v v+ = 10.0v, shdn 3 1.6v (shutdown) v+ = 16.5v, shdn 3 1.6v (shutdown) v+ = 16.5v, shdn = 0v (normal operation ) minimum start-up voltage max770/max771/max772 1.8 2.0 v max770?72 (internal feedback resistors) 2.0 16.5 max770?72c/e (external resistors) 3.0 16.5 max770?72mja (external resistors) 3.1 16.5 max773c/e 3.0 16.5 max773mjd 3.1 16.5 input voltage range v
max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers _______________________________________________________________________________________ 3 electrical characteristics (continued) (v+ = 5v, i load = 0ma, t a = t min to t max , unless otherwise noted. typical values are at t a = +25 c.) parameters symbol conditions min typ max units ref load regulation 0 m a i ref 100 m a max77_c/e 4 10 mv max77_m 4 15 ref line regulation 3v v+ 16.5v 40 100 m v/v fb trip-point voltage v fb max77_c 1.4700 1.50 1.5300 v max77_e 1.4625 1.50 1.5375 max77_m 1.4550 1.50 1.5450 fb input current i fb max77_c 20 na max77_e 40 max77_m 60 shdn input high voltage v ih v+ = 2.0v to 16.5v 1.6 v shdn input low voltage v il max77_c/e, v+ = 2.0v to 16.5v 0.4 v shdn input current 1 m a lbi input current max773, v+ = 16.5v, lbi = 1.5v 20 na lbi hysteresis max773 20 lbi threshold voltage max773, lbi falling max77_c 1.4700 1.50 1.5300 v max77_e 1.4625 1.50 1.5375 max77_m 1.4550 1.50 1.5450 lbo leakage current max773, v+ = 16.5v, v lbo = 16.5v 0.01 1.00 m a lbo output voltage low v ol max773, v+ = 5v, lbo sinking 1ma 0.1 0.4 v v+ = 16.5v, shdn = 0v or v+ mv current-limit trip level v cs v+ = 5v to 16.5v 170 200 230 mv v shunt max773, i shunt = 1ma to 20ma, sgnd = 0v, c shunt = 0.1 m f 5.5 6.3 v cs input current 0.01 1 m a ext rise time v+ = 5v, 1nf from ext to ground (note 3) 55 ns ext fall time v+ = 5v, 1nf from ext to ground (note 3) 55 ns supply voltage in shunt mode note 1: output voltage guaranteed using preset voltages. see figures 7a?d for output current capability versus input voltage. note 2: output voltage line and load regulation depend on external circuit components. note 3: for the max773, ext is exth and extl shorted together. lbi delay 5mv overdrive 2.5 s max77_m, v+ = 2.0v to 16.5v 0.2
0 1 2 3 4 -75 -50 -25 0 25 50 75 100 125 supply current vs. temperature temperature (?) supply current (ma) v out = 12v, v in = 5v circuit of figure 2b bootstrapped mode entire circuit schottky diode leakage excluded max770?-07 0 0.2 0.4 0.6 0.8 2 4 6 8 10 12 supply current vs. supply voltage supply voltage (v) supply current (ma) v out = 12v non-bootstrapped circuit of figure 2c bootstrapped circuit of figure 2b max770?-08 0 100 150 200 250 50 2 4 6 8 10 12 ext rise/fall time vs. supply voltage v+ (v) ext rise/fall time (ns) c ext = 2200pf c ext = 1000pf c ext = 446pf c ext = 100pf max770?-09 100 50 0.001 0.01 0.1 1 max772 efficiency vs. output current (bootstrapped) 60 output current (a) efficiency (%) 70 80 90 v out = 15v, circuit of figure 2b max772 substituted for max771 v in = 12v v in = 9v v in = 6v v in = 5v v in = 3v max770?-03 50 60 70 80 90 100 0.001 0.01 1 max771 efficiency vs. output current (bootstrapped) output current (a) efficiency (%) 0.1 v in = 6v v in = 5v v in = 3v v in = 9v v out = 12v circuit of figure 2b max770?-02 100 50 0.001 0.01 0.1 1 max770 efficiency vs. output current (bootstrapped) 60 output current (a) efficiency (%) 70 80 90 v in = 3v v in = 3.5v v out = 5v circuit of figure 2a v in = 4v max770?-01 max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 4 _______________________________________________________________________________________ __________________________________________ t ypical operating characteristics (t a = +25 c, unless otherwise noted.) 70 80 90 100 0.001 0.01 0.1 10 1 max771 efficiency vs. output current (non-bootstrapped) output current (a) efficiency ( % ) v in = 9v v in = 6v v in = 5v v out = 12v circuit of figure 2c max770?-04 0 100 200 300 400 500 600 700 1.0 max770 load current vs. minimum start-up input voltage minimum start-up input voltage (v) load current (ma) 3.0 1.5 2.5 3.5 2.0 above 3.4v, the circuit starts up under maximum load conditions v out = 5v circuit of figure 2a max770?-05 0 100 200 300 400 500 2.0 max771 load current vs. minimum start-up input voltage minimum start-up input voltage (v) load current (ma) 4.0 2.5 3.5 3.0 above 3.5v the circuit starts up under maximum load conditions v out = 12v circuit of figure 2b max770?-06
max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers _______________________________________________________________________________________ 5 250 0 -60 -20 60 140 reference output resistance vs. temperature 50 max770?-10 temperature ( c) reference output resistance ( w ) 20 100 150 -40 0 80 40 120 100 200 100? 50? 10? 1.502 -60 -20 60 140 reference vs. temperature max770?-11 temperature ( c) reference (v) 20 100 -40 0 80 40 120 1.500 1.498 1.496 1.494 1.492 1.504 1.506 4.0 -60 -20 60 140 shutdown current vs. temperature max770?-12 temperature ( c) i cc (?) 20 100 -40 0 80 40 120 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 v+ = 15v v+ = 4v v+ = 8v 15.5 16.0 16.5 -60 -30 0 30 60 90 120 150 maximum switch on-time vs. temperature temperature (?) t on(max) (?) max770?-13 2.20 2.25 2.30 -60 -30 0 30 60 90 120 150 minimum switch off-time vs. temperature temperature (?) t off(min) (?) max770?-14 6.0 7.0 8.0 -60 -30 0 30 60 90 120 150 maximum switch on-time/ minimum switch off-time ratio vs. temperature temperature (?) t on(max)/ t off(min) ratio max770?-15 7.5 6.5 ____________________________ t ypical operating characteristics (continued) (t a = +25 c, unless otherwise noted.)
max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 6 _______________________________________________________________________________________ v in = 2.9v, i out = 0.9a a: ext voltage, 5v/div b: inductor current 1a/div c: v out ripple 100mv/div, ac-coupled max 770 hea vy-l oad swit chng wa vef or ms 20 m s/div v out 0 a i lim i lim 2 b c 0 v+ = 3v, i out = 165ma a: ext voltage, 5v/div b: inductor current, 1a/div c: v out ripple 100mv/div, ac-coupled max770 light-load switching waveforms 20 m s/div 0 b a c i lim 2 i out = 0.7a a: v in , 2.7v to 4.5v, 2v/div b: v out ripple, 100mv/div, ac-coupled max770 line-transient response a b 4.5v 2.7v 0 2ms/div v in = 3v a: load current 0.5a/div (0a to 1a) b: v out ripple, 100mv/div, ac-coupled max770 load-transient response 2ms/div a b 0 ____________________________ t ypical operating characteristics (continued) (circuit of figure 2a, t a = +25 c, unless otherwise noted.)
max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers _______________________________________________________________________________________ 7 v in = 3v, i out = 0.5a a: shdn, 2v/div b: v out , 2v/div max770 exiting shutdown a b 0 0 200 m s/div ______________________________________________________________ pin description ____________________________ t ypical operating characteristics (continued) (circuit of figure 2a, t a = +25 c, unless otherwise noted.) pin name function max773 1 ext gate drive for external n-channel power transistor 2 3 v+ 3 6 fb 4 7 shdn 5 8 ref 6 agnd analog ground 7 9 gnd high-current ground return for the output driver 8 11 cs 1 v12 2 v5 max770 max771 max772 power-supply input. also acts as a voltage-sense point when in bootstrapped mode for the max770/max771/max772, or as a shunt regulator when sgnd is connected to ground for the max773. bypass to sgnd with 0.1 m f when using the shunt regulator. feedback input for adjustable-output operation. connect to ground for fixed-output operation. use a resistor divider network to adjust the output voltage. see setting the output voltage section. active-high ttl/cmos logic-level shutdown input. in shutdown mode, v out is a diode drop below v+ (due to the dc path from v+ to the output) and the supply current drops to 5 m a maximum. connect to ground for normal operation. 1.5v reference output that can source 100 m a for external loads. bypass to gnd with 0.1 m f. the reference is disabled in shutdown. positive input to the current-sense amplifier. connect the current-sense resistor between cs and gnd. input sense point for 12v-output operation. connect v out to v12 for 12v-output operation. leave unconnected for adjustable-output operation. input sense point for 5v-output operation. connect v out to v5 for 5v-output operation. leave unconnected for adjustable-output operation. 4 lbo 5 lbi input to the internal low-battery comparator. tie to gnd or v+ if not used. 10 sgnd shunt regulator ground. leave unconnected if the shunt regulator is not used. low-battery output is an open-drain output that goes low when lbi is less than 1.5v. connect to v+ through a pull-up resistor. leave floating if not used. lbo is high impedance in shutdown mode.
max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 8 _______________________________________________________________________________________ _______________ detailed description the max770?ax773 are bicmos, step-up, switch- mode power-supply controllers that provide preset 5v, 12v, and 15v output voltages, in addition to adjustable- output operation. their unique control scheme com - bines the advantages of pulse-frequency modulation (low supply current) and pulse-width modulation (high efficiency with heavy loads), providing high efficiency over a wide output current range, as well as increased output current capability over previous pfm devices. in addition, the external sense resistor and power transistor allow the user to tailor the output current capability for each application. figure 1 shows the max770?ax773 block diagram. the max770?ax773 offer three main improvements over prior pulse-skipping control solutions: 1) the con - verters operate with tiny (5mm height and less than 9mm diameter) surface-mount inductors due to their 300khz switching frequency; 2) the current-limited pfm control scheme allows 87% efficiencies over a wide range of load currents; and 3) the maximum supply current is only 110 a. the max773 can be configured to operate from an internal 6v shunt regulator, allowing very high input/out - put voltages. its output can be configured for an adjustable voltage or for one of three fixed voltages (5v, 12v, or 15v), and it has a power-fail comparator for low-battery detection. all devices have shutdown capability, reducing the supply current to 5 a max. bootstrapped/non-bootstrapped modes figures 2 and 3 show standard application circuits for bootstrapped and non-bootstrapped modes. in boot - strapped mode, the ic is powered from the output (v out , which is connected to v+) and the input voltage range is 2v to v out . the voltage applied to the gate of the external power transistor is switched from v out to ground, providing more switch gate drive and thus reducing the transistor? on resistance. in non-bootstrapped mode, the ic is powered from the input voltage (v+) and operates with minimum supply current. in this mode, fb is the output voltage sense point. since the voltage swing applied to the gate of the external power transistor is reduced (the gate swings from v+ to ground), the power transistor? on resistance increases at low input voltages. however, the supply current is also reduced because v+ is at a lower volt - age, and because less energy is consumed while charging and discharging the external mosfet? gate capacitance. the minimum input voltage for the max770?ax773 is 3v when using external feedback resistors. with supply voltages below 5v, bootstrapped mode is recommended. note: when using the max770/max771/max772 in non-bootstrapped mode, there is no preset output operation because v+ is also the output voltage sense point for fixed-output operation. external resistors must be used to set the output voltage. use 1% external feedback resistors when operating in adjustable-output mode (figures 2c, 2d, 3b, 3d, 3e) to achieve an overall output voltage accuracy of 5%. the max773 can be operated in non-bootstrapped mode without using external feedback resistors because v+ does not act as the output voltage sense point with preset-output operation. to achieve high - est efficiency, operate in bootstrapped mode when - ever possible. max773 shunt-regulator operation the max773 has an internal 6v shunt regulator that allows the device to step up from very high input voltages (figure 4). pin name function max770 max771 max772 max773 13 exth 12 extl low-level gate/base drive for external power transistor. connect to the gate of an external n-channel mosfet or to the base of an external npn transistor. 14 v15 input sense point for 15v-output operation. connect v out to v15 for 15v-output operation. leave unconnected for adjustable-output operation _________________________________________________ pin description (continued) high-level gate/base drive for external power transistor. connect to extl when using an external n-channel mosfet. when using an external npn transistor, connect a resistor r base from exth to the base of the npn to set the maximum base-drive current.
floating the shunt-regulator ground (sgnd) disables the shunt regulator. to enable it, connect sgnd to gnd. the shunt regulator requires 1ma minimum cur - rent for proper operation; the maximum current must not exceed 20ma. the max773 operates in non-boot - strapped mode when the shunt regulator is used, and ext swings between the 6v shunt-regulator voltage and gnd. when using the shunt regulator, use an n-channel pow - er fet instead of an npn power transistor as the power switch. otherwise, excessive base drive will collapse the shunt regulator. external power-transistor control circuitry pfm control scheme the max770?ax773 use a proprietary current-limited pfm control scheme to provide high efficiency over a wide range of load currents. this control scheme com - bines the ultra-low supply current of pfm converters (or pulse skippers) with the high full-load efficiency of pwm converters. unlike traditional pfm converters, the max770 max773 use a sense resistor to control the peak induc - tor current. they also operate with high switching max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers _______________________________________________________________________________________ 9 v+ ext control 1.5v reference q trig q s f/f r q trig low-voltage oscillator 2.5v 0.1v 0.2v one-shot one-shot current-sense amplifier dual-mode comparator lbo v15 v12 v5 fb lbi ref 200mv error comparator shdn v+ sgnd 6v exth extl ext cs max773 only max770 max771 max772 max770 max771 max772 bias circuitry n n n max770?ax773 max773 only figure 1. block diagram
max770?ax773 frequencies (up to 300khz), allowing the use of tiny external components. as with traditional pfm converters, the power transistor is not turned on until the voltage comparator senses that the output is out of regulation. however, unlike tra - ditional pfm converters, the max770?ax773 switch using the combination of a peak current limit and a pair of one-shots that set the maximum on-time (16 s) and minimum off-time (2.3 s); there is no oscillator. once off, the minimum off-time one-shot holds the switch off for 2.3 s. after this minimum time, the switch either 1) stays off if the output is in regulation, or 2) turns on again if the output is out of regulation. the control circuitry allows the ics to operate in contin - uous-conduction mode (ccm) while maintaining high efficiency with heavy loads. when the power switch is 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 10 ______________________________________________________________________________________ max770 v in = 3v ref shdn fb agnd gnd n 7 ext cs c2 0.1 m f c1 100 m f l1 22 m h d1 1n5817 mtp3055el r sense 75m w c4 300 m f c3 0.1 m f 5 4 3 6 1 8 2 v+ v out = 5v @ 1a figure 2a. 5v preset output, bootstrapped figure 2b. 12v preset output, bootstrapped figure 2c. 12v output, non-bootstrapped figure 2d. 9v output, bootstrapped max770 max771 max772 v in = 5v ref shdn agnd gnd n 7 ext cs fb l1 22 m h d1 1n5817 r1 18k c4 200 m f c3 0.1 m f 5 4 6 1 8 3 2 v+ c1 68 m f v out = 12v @ 0.5a r2 127k r sense 100m w c2 0.1 m f v out v ref r2 = (r1) ( -1 ) v ref = 1.5v max770 max771 max772 ref shdn agnd gnd n 7 ext cs fb c1 47 m f l1 20 m h d1 1n5817 r1 28k c4 100 m f c3 0.1 m f 5 4 6 1 8 3 2 v+ v out = 9v r2 140k r sense c2 0.1 m f v out v ref r2 = (r1) ( -1 ) v ref = 1.5v si9410dy v in = 4v max771 v in = 5v ref shdn fb agnd gnd n 7 ext cs c2 0.1 m f c1 68 m f l1 22 m h d1 1n5817 si9410dy r sense 100m w c4 200 m f c3 0.1 m f 5 4 3 6 1 8 2 v+ v out = 12v @ 0.5a
max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers ______________________________________________________________________________________ 11 gnd max773 c3 0.1 m f v out = 12v v+ r4 63.4k (1%) r3 10k (1%) sgnd lbo exth 8 5 7 6 extl cs v12 v15 v5 ref lbi shdn fb 2 14 1 10 4 13 12 11 9 r sense n si9410dy c4 c2 0.1 m f v in l1 22 m h d1 1n5817 100k c1 r 4 = r3 ( v trip -1 ) v ref min nominal max 10.6 11.0 11.4 v trip (v) 3 v ref = 1.5v gnd max773 c3 0.1 m f v+ extl cs v12 8 5 7 v5 fb sgnd lbo ref lbi shdn 4 10 12 11 1 2 6 9 r sense 0.4 w c4 150 m f c2 0.1 m f d1 1n5818 v15 14 exth 13 c1 47 m f 3 l1 150 m h 910 w r1 34k r2 510k ztx694b v out = 24v @ 30ma v in = 5v v out v ref r2 = (r1) ( -1 ) v ref = 1.5v gnd max773 c3 0.1 m f v+ extl cs v5 8 7 6 v15 v12 sgnd lbo ref shdn fb 4 10 v in = 5v 12 11 2 14 1 9 r sense c4 c2 0.1 m f d1 1n5817 exth 13 3 l1 22 m h v out = 15v lbi n si9410dy 5 c1 gnd max773 c3 0.1 m f v+ extl cs v5 8 5 7 v15 v12 lbo ref lbi shdn 4 v in 12 11 2 14 1 9 r sense c4 d1 1n5817 exth 13 3 l1 20 m h v out = 16v sgnd n 10 c1 c2 0.1 m f fb 6 r2 133k r1 13.7k v out v ref r2 = (r1) ( -1 ) v ref = 1.5v si9410dy figure 3a. 12v preset output, bootstrapped, n-channel power mosfet figure 3b. 24v output, non-bootstrapped, npn power transistor figure 3c. 15v preset output, non-bootstrapped n-channel power mosfet figure 3d. 16v output, bootstrapped, n-channel power mosfet
max770?ax773 turned on, it stays on until either 1) the maximum on- time one-shot turns it off (typically 16 s later), or 2) the switch current reaches the peak current limit set by the current-sense resistor. to increase light-load efficiency, 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 error comparator holds the mosfet off and the current limit remains at one-half the peak current limit. if the output voltage is still out of regulation after two pulses, the current limit for the next pulse is raised to the peak current limit set by the external sense resistor (see inductor current waveforms in the typical operating characteristics ). the max770?ax773 switching frequency is variable (depending on load current and input voltage), causing variable switching noise. however, the subharmonic noise generated does not exceed the peak current limit times the filter capacitor equivalent series resistance (esr). for example, when generating a 12v output at 500ma from a 5v input, only 180mv of output ripple occurs using the circuit of figure 2b. low-voltage start-up oscillator the max770/max771/max772 feature a low input volt - age start-up oscillator that guarantees start-up with no load down to 2v when operating in bootstrapped mode and using internal feedback resistors. at these low volt - ages, the supply voltage is not large enough for proper error-comparator operation and internal biasing. the start-up oscillator has a fixed 50% duty cycle and the max770/max771/max772 disregard the error-com - parator output when the supply voltage is less than 2.5v. above 2.5v, the error-comparator and normal one- shot timing circuitry are used. the low voltage start-up circuitry is disabled if non-bootstrapped mode is select - ed (fb is not tied to ground). the max773 does not provide the low-voltage 50% duty-cycle oscillator. its minimum start-up voltage is 3v for all modes. external transistor an n-fet power switch is recommended for the max770/max771/max772. the max773 can drive either an n-channel mosfet (n-fet) or an npn because it provides two separate 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 12 ______________________________________________________________________________________ gnd max773 c3 0.1 m f v+ extl cs v5 8 5 7 v15 v12 lbo ref lbi shdn 4 12 11 2 14 1 9 r sense 1.0 w c4 100 m f d1 mur115 exth 13 3 l1 250 m h v out = 100v @ 10ma sgnd n 10 c1 47 m f fb 6 r2 732k (1%) r1 11.3k (1%) si9420dy r shunt 3k c2 0.1 m f v in = 24v to 28v v out v ref r2 = (r1) ( -1 ) v ref = 1.5v max773 r shunt c2 0.1 m f sgnd 6v (typ) v+ v in r shunt = v in (min) - v shunt ( max ) i shunt * * see text for i shunt calculation 3 10 figure 3e. 100v output, shunt regulator, n-channel power mosfet figure 4. max773 shunt regulator
drive outputs (exth and extl) that operate 180 out of phase (figures 3a and 3b). in figure 3b, the resistor in series with exth limits the base current, and extl (which is connected directly to the base) turns the transistor off. shutdown mode when shdn is high, the max770?ax773 enter shut - down mode. in this mode, the internal biasing circuit - ry is turned off (including the reference) and v out falls to a diode drop below v in (due to the dc path from the input to the output). in shutdown mode, the supply current drops to less than 5 a. shdn is a ttl/cmos logic-level input. connect shdn to gnd for normal operation. the max773? shunt regulator is not disabled in shut - down mode. low-battery detector the max773 provides a low-battery comparator that compares the voltage on lbi to the reference voltage. when the lbi voltage is below v ref , lbo (an open- drain output) goes low. the low-battery comparator? 20mv of hysteresis adds noise immunity, preventing repeated triggering of lbo. use a resistor-divider network between v+, lbi, and gnd to set the desired trip voltage v trip . lbo is high impedance in shutdown mode. __________________ design pr ocedur e setting the output voltage to set the output voltage, first determine the mode of operation, either bootstrapped or non-bootstrapped. bootstrapped mode provides more output current capability, while non-bootstrapped mode reduces the supply current (see typical operating characteristics ). if a decaying voltage source (such as a battery) is used, see the additional notes in the low input voltage operation section. use the max770/max771/max772 unless one or more of the following conditions applies. if one or more of the following is true, use the max773: 1) an npn power transistor will be used as the power switch 2) the lbi/lbo function is required 3) the shunt regulator must accommodate a high input voltage 4) preset-output non-bootstrapped operation is desired?or example, to reduce the no-load supply current in a 5v to 12v application. see table 1 for a summary of operating characteristics and requirements for the ics in bootstrapped and non- bootstrapped modes. the max770?ax773? output voltage can be adjust - ed from very high voltages down to 3v, using external resistors r1 and r2 configured as shown in figure 5. for adjustable-output operation, select feedback resis - tor r1 in the range of 10k w to 500k . r2 is given by: v out r2 = (r1) ( -1 ) v ref where v ref equals 1.5v. for preset-output operation, tie fb to gnd (this forces bootstrapped-mode operation for the max770/max771/max772). configure the max773 for a preset voltage of 5v, 12v, or 15v by connecting the output to the corresponding sense input pin (i.e., v5, v12, or v15). fb must be tied to ground for preset-output operation. leave all unused sense input pins unconnected. failure to do so will cause an incorrect output voltage. the max773 can provide a preset output voltage in both bootstrapped and non- bootstrapped modes. figures 2 and 3 show various circuit configurations for bootstrapped/non-bootstrapped, preset/adjustable operation. shunt-regulator operation when using the shunt regulator, connect sgnd to ground and place a 0.1 f capacitor between v+ and sgnd, as close to the ic as possible. increase c2 to 1.0 f to improve shunt regulators performance with heavy loads. select r shunt such that 1ma i shunt 20ma. max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers ______________________________________________________________________________________ 13 max770 max771 max772 max773 r1 r2 gnd fb v out r1 = 10k to 500k v out v ref r2 = r1 ( -1 ) v ref = 1.5v figure 5. adjustable output circuit
max770?ax773 use an n-channel fet as the power switch when using the shunt regulator (see max773 shunt-regulator operation in the detailed description ). the shunt-regu - lator current powers the max773 and also provides the fet gate-drive current, which depends largely on the fet? total gate charge at v gs = 5v. to determine the shunt-resistor value, first determine the maximum shunt current required. i shunt = i supp + i gate see n-channel mosfets in the power-transistor selection section to determine i gate . determine the shunt-resistor value using the following equation: v in (min) - v shunt (max) r shunt (max) = i shunt where v shunt (max) is 6.3v. the shunt regulator is not disabled in shutdown mode, and continues to draw the calculated shunt current. if the calculated shunt regulator current exceeds 20ma, or if the shunt current exceeds 5ma and less shunt reg - ulator current is desired, use the circuit of figure 6 to provide increased drive and reduced shunt current when driving n-fets with large gate capacitances. select i shunt = 3ma. this provides adequate biasing current for this circuit, although higher shunt currents can be used. to prevent the shunt regulator from drawing current in shutdown mode, place a switch in series with the shunt resistor. 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 14 ______________________________________________________________________________________ max773(n)/max773(s) max770?ax773(n) fixed output available higher lower gnd to v out 2v to 5v (max770/max771/max772), 3v to 5v (max773) max770?ax773(n) higher 2v to 16.5v (max770/max771/max772), (internal feedback resistors) 3v to 16.5v (max770/max771/max772), (external feedback resistors) 3v to 16.5v (max773) bootstrapped* max770/max771/max772/ max773(n)/max773(s) adjustable output available lower gate-drive capacitive losses higher fet on resistance gnd to v+ gate drive 5v to 16.5v (max770/max771/max772), 5v and up (max773) normally recommended input voltage range lower no-load supply current 3v to 16.5v (max770/max771/max772), 3v and up (max773) possible input voltage range non-bootstrapped parameter table 1. bootstrapped vs. non-bootstrapped operation max773 cs fb sgnd r shunt n extl 100 w v+ c1 c2 0.1 m f v in l1 20 m h npn 2n2222a r2 r1 d1 v out c4 r sense pnp 2n2907a 3 10 13 12 11 6 exth figure 6. increased n-fet gate drive when using the shunt regulator *max773(s) indicates shunt mode; max773(n) indicates not in shunt mode.
determining r sense the typical operating characteristics graphs show the output current capability for various modes, sense resistors, and input/output voltages. use these graphs, along with the theoretical output current curves shown in figures 7a-7d, to select r sense . these theoretical curves assume that an external n-fet power switch is used. they were derived using the minimum (worst- case) current-limit comparator threshold value, and the inductance value. no tolerance was included for r sense . the voltage drop across the diode was assumed to be 0.5v, and the drop across the power switch r ds(on) and coil resistance was assumed to be 0.3v. to use the graphs, locate the graph with the appropriate output voltage or the graph having the nearest output voltage higher than the desired output voltage. on this graph, find the curve for the largest sense-resistor value with an output current that is ade - quate at the lowest input voltage. determining the inductor (l) practical inductor values range from 10 h to 300 h. 20 h is a good choice for most applications. in appli - cations with large input/output differentials, the ic? output current capability will be much less when the inductance value is too low, because the ic will always operate in discontinuous mode. if the inductor value is too low, the current will ramp up to a high level before the current-limit comparator can turn off the switch. the minimum on-time for the switch (t on (min)) is approximately 2 s; select an inductor that allows the current to ramp up to i lim /2 in no less than 2 s. choosing a value of i lim /2 allows the half-size current pulses to occur, increasing light-load efficiency and minimizing output ripple. max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers ______________________________________________________________________________________ 15 maximum output current (a) 0 input voltage (v) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 2 3 4 5 r sense = 40m w r sense = 50m w r sense = 75m w r sense = 200m w r sense = 100m w v out = 5v l = 22 m h maximum output current (a) 0 input voltage (v) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 2 4 6 8 10 12 r sense = 200m w r sense = 100m w r sense = 40m w r sense = 50m w r sense = 75m w v out = 12v l = 22 m h figure 7a. maximum output current vs. input voltage (v out = 5v) figure 7b. maximum output current vs. input voltage (v out = 12v) figure 7c. maximum output current vs. input voltage (v out = 15v) figure 7d. maximum output current vs. input voltage (v out = 24v) maximum output current (a) 0 input voltage (v) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 2 4 6 8 10 12 14 16 r sense = 200m w r sense = 100m w v out = 15v l = 22 m h r sense = 40m w r sense = 50m w r sense = 75m w maximum output current (a) 0 2 input voltage (v) 0.8 6 10 14 0.2 0.4 0.6 v out = 24v l =150 m h r sense = 100m w r sense = 200m w r sense = 400m w
max770?ax773 the standard operating circuits use a 22 h inductor. if a different inductance value is desired, select l such that: v in (max) x t on (min) l 3 i li m / 2 larger inductance values tend to increase the start-up time slightly, while smaller inductance values allow the coil current to ramp up to higher levels before the switch turns off, increasing the ripple at light loads. inductors with a ferrite core or equivalent are recom - mended; powder iron cores are not recommended for use with high switching frequencies. make sure the inductor? saturation current rating (the current at which the core begins to saturate and the inductance starts to fall) exceeds the peak current rating set by r sense . however, it is generally acceptable to bias the inductor into saturation by approximately 20% (the point where the inductance is 20% below the nominal value). for highest efficiency, use a coil with low dc resistance, preferably under 20m . to minimize radiated noise, use a toroid, a pot core, or a shielded coil. table 2 lists inductor suppliers and specific recom - mended inductors. power transistor selection use an n-channel mosfet power transistor with the max770/max771/max772 (figure 8a). use an n-fet whenever possible with the max773. an npn transistor can be used, but be extremely careful when determining the base current (see npn transistors section). an npn transistor is not recom - mended when using the shunt regulator. n-channel mosfets to ensure the external n-channel mosfet (n-fet) is turned on hard, use logic-level or low-threshold n-fets when the input drive voltage is less than 8v. this applies even in bootstrapped mode, to ensure start-up. n-fets provide the highest efficiency because they do not draw any dc gate-drive current, but they are typi - cally more expensive than npn transistors. when using an n-fet with the max773, connect exth and extl to the n-fet? gate (figure 8b). when selecting an n-fet, three important parameters are the total gate charge (q g ), on resistance (r ds(on) ), and reverse transfer capacitance (c rss ). q g takes into account all capacitances associated with charging the gate. use the typical q g value for best results; the maximum value is usually grossly over- specified since it is a guaranteed limit and not the mea - sured value. the typical total gate charge should be 50nc or less. with larger numbers, the ext pins may not be able to adequately drive the gate. the ext rise/fall time with various capacitive loads as shown in the typical operating characteristics . 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 16 ______________________________________________________________________________________ max770 max771 max772 n ext cs r sense max773 npn exth extl cs l r sense r base i c(peak) i b figure 8a. use an n-channel mosfet with the max770/max771/max772 figure 8b. using an n-channel mosfet with the max773 figure 8c. using an npn transistor with the max773 max773 n exth extl cs l r sense
the two most significant losses contributing to the n-fet? power dissipation are i 2 r losses and switching losses. select a transistor with low r ds(on) and low c rss to minimize these losses. determine the maximum required gate-drive current from the q g specification in the n-fet data sheet. the max773? maximum allowed switching frequency during normal operation is 300khz; but at start-up the maximum frequency can be 500khz, so the maximum current required to charge the n-fet? gate is f(max) x q g (typ). use the typical q g number from the transistor data sheet. for example, the si9410dy has a q g (typ) of 17nc (at v gs = 5v), therefore the current required to charge the gate is: i gate (max) = (500khz) (17nc) = 8.5ma. the bypass capacitor on v+ (c2) must instantaneously furnish the gate charge without excessive droop (e.g., less than 200mv): q g d v+ = c2 continuing with the example, d v+ = 17nc/0.1 f = 170mv. use i gate when calculating the appropriate shunt resistor. see the shunt regulator operation section. figure 2a? application circuit uses an mtd3055el logic-level n-fet with a guaranteed threshold voltage (v th ) of 2v. figure 2b? application circuit uses an 8-pin si9410dy surface-mount n-fet that has 50m on resistance with 4.5v v gs , and a guaranteed v th of less than 3v. npn transistors the max773 can drive npn transistors, but be extremely careful when determining the base-current requirements. too little base current can cause exces - sive power dissipation in the transistor; too much base current can cause the base to oversaturate, so the tran - sistor remains on continually. both conditions can dam - age the transistor. when using the max773 with an npn transistor, con - nect extl to the transistor? base, and connect r base between exth and the base (figure 8c). to determine the required peak inductor current, i c(peak ), observe the typical operating characteristics efficiency graphs and the theoretical output current capability vs. input voltage graphs to determine a sense resistor that will allow the desired output current. divide the 170mv worst-case (smallest) voltage across the current-sense amplifier v cs (max) by the sense- resistor value. to determine i b , set the peak inductor current (i lim) equal to the peak transistor collector cur - rent i c(peak) . calculate i b as follows: i b = i lim /? use the worst-case (lowest) value for ?given in the transistor? electrical specification, where the collector current used for the test is approximately equal to i lim . it may be necessary to use even higher base currents (e.g., i b = i li m / 10), although excessive i b may impair operation by extending the transistor? turn-off time. r base is determined by: ( v exth - v be - v cs ( mi n ) ) r base = i b where v exth is the voltage at v+ (in bootstrapped mode v exth is the output voltage), v be is the 0.7v transistor base-emitter voltage, v cs (min) is the voltage drop across the current-sense resistor, and i b is the minimum base current that forces the transistor into saturation. this equation reduces to (v+ - 700mv - 170mv) / i b . for maximum efficiency, make r base as large as pos - sible, but small enough to ensure the transistor is always driven near saturation. highest efficiency is obtained with a fast-switching npn transistor (f t 3 150mhz) with a low collector-emitter saturation voltage and a high current gain. a good transistor to use is the zetex ztx694b. diode selection the max770?ax773? high switching frequency demands a high-speed rectifier. schottky diodes such as the 1n5817?n5822 are recommended. make sure that the schottky diode? average current rating exceeds the peak current limit set by r sense , and that its breakdown voltage exceeds v out . for high-temper - ature applications, schottky diodes may be inadequate due to their high leakage currents; high-speed silicon diodes may be used instead. at heavy loads and high temperatures, the benefits of a schottky diode? low for - ward voltage may outweigh the disadvantages of its high leakage current. capacitor selection output filter capacitor the primary criterion for selecting the output filter capacitor (c2) is low effective series resistance (esr). the product of the peak inductor current and the output filter capacitor? esr determines the amplitude of the ripple seen on the output voltage. an os-con 300 f, 6.3v output filter capacitor has approximately 50m of esr and typically provides 180mv ripple when stepping up from 3v to 5v at 1a (figure 2a). max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers ______________________________________________________________________________________ 17
max770?ax773 smaller capacitors are acceptable for light loads or in applications that can tolerate higher output ripple. since the output filter capacitor? esr affects efficien - cy, use low-esr capacitors for best performance. the smallest low-esr surface-mount tantalum capacitors currently available are the sprague 595d series. sanyo os-con organic semiconductor through-hole capaci - tors and the nichicon pl series also exhibit low esr. see table 2. input bypass capacitors the input bypass capacitor (c1) reduces peak currents drawn from the voltage source and also reduces noise at the voltage source caused by the switching action of the max770?ax773. the input voltage source imped - ance determines the size of the capacitor required at the v+ input. as with the output filter capacitor, a low- esr capacitor is recommended. for output currents up to 1a, 150 f (c1) is adequate, although smaller bypass capacitors may also be acceptable. bypass the ic with a 0.1 f ceramic capacitor (c2) placed close to the v+ and gnd pins. reference capacitor bypass ref with a 0.1 f capacitor (c3). ref can source up to 100 a of current. setting the low-battery-detector voltage to set the low-battery detector? falling trip voltage (v trip (falling)), select r3 between 10k w and 500k w (figure 9), and calculate r4 as follows: v trip - v ref r4 = (r3) ( ) v ref where v ref = 1.5v. the rising trip voltage is higher because of the com - parator? approximately 20mv of hysteresis, and is determined by: r4 v trip (rising) = (v ref + 20mv) (1 + ) r3 connect a high value resistor (larger than r3 + r4) between lbi and lbo if additional hysteresis is required. connect a pull-up resistor (e.g., 100k w ) between lbo and v+. tie lbi to gnd and leave lbo floating if the low-battery detector is not used. __________ applications infor mation max773 operation with high input/output voltages the max773? shunt regulator input allows high volt - ages to be converted to very high voltages. since the max773 runs off the 6v shunt (bootstrapped operation is not allowed), the ic will not see the high input volt - age. use an external logic-level n-fet as the power switch, since only 6v of v gs are available. also, make sure all external components are rated for very high output voltage. figure 3e shows a circuit that converts 28v to 100v. low input voltage operation when using a power supply that decays with time (such as a battery), the n-fet transistor will operate in its linear region when the voltage at ext approaches the threshold voltage of the fet, dissipating excessive power. prolonged operation in this mode may damage the fet. this effect is much more significant in non- bootstrapped mode than in bootstrapped mode, since bootstrapped mode typically provides much higher v gs voltages. to avoid this condition, make sure v ext is above the v th of the fet, or use a voltage detector (such as the max8211) to put the ic in shutdown mode once the input supply voltage falls below a predeter - mined minimum value. excessive loads with low input voltages can also cause this condition. 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 18 ______________________________________________________________________________________ max773 lbi lbo gnd v+ r4 v in r5 100k r3 low-battery output v trip v ref r4 = r3 ( -1 ) v ref = 1.5v figure 9. input voltage monitor circuit
starting up under load the typical operating characteristics show the start- up voltage vs. load current graph for bootstrapped- mode operation. this graph depends on the type of power switch used. the max770?ax773 are not designed to start up under full load in boot- strapped mode with low input voltages. layout considerations due to high current levels and fast switching wave - forms, which radiate noise, proper pc board layout is essential. protect sensitive analog grounds by using a star ground configuration. minimize ground noise by connecting gnd, the input bypass capacitor ground lead, and the output filter capacitor ground lead to a single point (star ground configuration). also, minimize lead lengths to reduce stray capacitance, trace resis - tance, and radiated noise. place input bypass capaci - tor c2 as close as possible to v+ and gnd. excessive noise at the v+ input may falsely trigger the timing circuitry, resulting in short pulses at ext. if this occurs it will have a negligible effect on circuit efficien - cy. if desired, place a 4.7 f directly across the v+ and gnd pins (in parallel with the 0.1 f c2 bypass capaci - tor) to reduce the noise at v+. max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers ______________________________________________________________________________________ 19 table 2. component suppliers production inductors capacitors transistors surface mount matsuo 267 series sprague 595d series through hole sumida cd54 series cdr125 series coiltronics ctx20 series motorola 1n5817?n5822 mur115 (high voltage) nihon ec10 series diodes sumida rch855 series rch110 series renco rl1284-18 sanyo os-con series nichicon pl series united chemi-con lxf series npn zetex ztx694b coiltronics matsuo usa: (714) 969-2491 (714) 960-6492 japan: 81-6-337-6450 81-6-337-6456 nichicon usa: (847) 843-7500 (847) 843-2798 nihon usa: (805) 867-2555 (805) 867-2698 renco usa: (516) 586-5566 (516) 586-5562 sanyo usa: (619) 661-6835 (619) 661-1055 japan: 81-7-2070-6306 81-7-2070-1174 sumida usa: (847) 956-0666 japan: 81-3-3607-5111 81-3-3607-5144 united chemi-con usa: (714) 255-9500 (714) 255-9400 n-fet siliconix si9410dy si9420dy (high voltage) motorola mtp3055el mtd20n03hdl usa: (561) 241-7876 (561) 241-9339 supplier phone fax zetex usa: (516) 543-7100 (516) 864-7630 uk: 44-61-627-4963 44-61-627-5467
max770?ax773 5v/12v/15v or adjustable, high-ef ficiency , low i q , step-up dc-dc contr ollers 20 ______________________________________________________________________________________ 14 13 12 11 10 9 8 1 2 3 4 5 6 7 v15 exth extl cs lbo v+ v5 v12 max773 sgnd gnd ref shdn fb lbi dip/so ___ or dering infor mation (continued) ____ pin configurations (continued) top view _________________ chip t opographies transistor count: 501; substrate connected to v+. transistor count: 501; substrate connected to v+. exth extl cs sgnd gnd gnd v5 v12 v15 v+ lbo lbi fb shdn ref 0.126" (3.200mm) 0.080" (2.032mm) max770/max771/max772 max773 v+ fb 0.126" (3.200mm) 0.080" (2.032mm) ext cs gnd agnd shdn ref 14 cerdip -55 c to +125 c max773mjd 14 narrow so -40 c to +85 c max773esd 14 plastic dip -40 c to +85 c max773epd dice* 0 c to +70 c max773c/d 14 so 0 c to +70 c max773csd 14 plastic dip 0 c to +70 c max773 cpd 8 cerdip -55 c to +125 c max772mja 8 so -40 c to +85 c max772esa 8 plastic dip -40 c to +85 c max772epa dice* 0 c to +70 c max772c/d 8 so 0 c to +70 c max772csa 8 plastic dip 0 c to +70 c max772 cpa 8 cerdip -55 c to +125 c max771mja 8 so -40 c to +85 c max771esa 8 plastic dip -40 c to +85 c max771epa dice* 0 c to +70 c max771c/d 8 so 0 c to +70 c max771csa 8 plastic dip 0 c to +70 c max771 cpa pin-package temp. range part *contact factory for dice specifications.

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