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lm2677 simple switcher ? high efficiency 5a step-down voltage regulator with sync general description the lm2677 series of regulators are monolithic integrated circuits which provide all of the active functions for a step-down (buck) switching regulator capable of driving up to 5a loads with excellent line and load regulation characteris- tics. high efficiency ( > 90%) is obtained through the use of a low on-resistance dmos power switch. the series consists of fixed output voltages of 3.3v, 5v and 12v and an adjust- able output version. the simple switcher concept provides for a complete design using a minimum number of external components. the switching clock frequency can be provided by an inter- nal fixed frequency oscillator (260khz) or from an externally provided clock in the range of 280khz to 400khz which al- lows the use of physically smaller sized components. a fam- ily of standard inductors for use with the lm2677 are avail- able from several manufacturers to greatly simplify the design process. the external sync clock provides direct and precise control of the output ripple frequency for consistent filtering or frequency spectrum positioning. the lm2677 series also has built in thermal shutdown, cur- rent limiting and an on/off control input that can power down the regulator to a low 50a quiescent current standby condition. the output voltage is guaranteed to a 2% toler- ance. features n efficiency up to 92% n simple and easy to design with (using off-the-shelf external components) n 100 m w dmos output switch n 3.3v, 5v and 12v fixed output and adjustable (1.2v to 37v ) versions n 50a standby current when switched off n 2%maximum output tolerance over full line and load conditions n wide input voltage range: 8v to 40v n external sync clock capability (280khz to 400khz) n 260 khz fixed frequency internal oscillator n ?40 to +125c operating junction temperature range applications n simple to design, high efficiency ( > 90%) step-down switching regulators n efficient system pre-regulator for linear voltage regulators n battery chargers n communications and radio equipment regulator with synchronized clock frequency typical application simple switcher ? is a registered trademark of national semiconductor corporation. ds101301-3 april 2000 lm2677 simple switcher high efficiency 5a step-down voltage regulator with sync ? 2000 national semiconductor corporation ds101301 www.national.com
connection diagram and ordering information to-263 package top view ds101301-1 order number lm2677s-3.3, lm2677s-5.0, lm2677s-12 or lm2677s-adj see nsc package number ts7b to-220 package top view ds101301-2 order number lm2677t-3.3, lm2677t-5.0, lm2677t-12 or lm2677t-adj see nsc package number ta07b lm2677 www.national.com 2
absolute maximum ratings (note 1) if military/aerospace specified devices are required, please contact the national semiconductor sales office/ distributors for availability and specifications. input supply voltage 45v on/off pin voltage ?0.1v to 6v switch voltage to ground ?1v to v in boost pin voltage v sw +8v feedback pin voltage ?0.3v to 14v power dissipation internally limited esd (note 2) 2 kv storage temperature range ?65c to 150c soldering temperature wave 4 sec, 260c infrared 10 sec, 240c vapor phase 75 sec, 219c operating ratings supply voltage 8v to 40v junction temperature range (t j ) ?40c to 125c electrical characteristics limits appearing in bold type face apply over the entire junction temperature range of operation, ?40c to 125c. specifications appearing in normal type apply for t a =t j = 25c. sync pin open cir- cuited. lm2677-3.3 symbol parameter conditions typical min max units (note 3) (note 4) (note 4) v out output voltage v in = 8v to 40v, 100ma i out 5a 3.3 3.234/ 3.201 3.366/ 3.399 v h efficiency v in = 12v, i load =5a 82 % lm2677-5.0 symbol parameter conditions typical min max units (note 3) (note 4) (note 4) v out output voltage v in = 8v to 40v, 100ma i out 5a 5.0 4.900/ 4.850 5.100/ 5.150 v h efficiency v in = 12v, i load =5a 84 % lm2677-12 symbol parameter conditions typical min max units (note 3) (note 4) (note 4) v out output voltage v in = 15v to 40v, 100ma i out 5a 12 11.76/ 11.64 12.24/ 12.36 v h efficiency v in = 24v, i load =5a 92 % lm2677-adj symbol parameter conditions typ min max units (note 3) (note 4) (note 4) v fb feedback voltage v in = 8v to 40v, 100ma i out 5a v out programmed for 5v 1.21 1.186/ 1.174 1.234/ 1.246 v h efficiency v in = 12v, i load =5a 84 % lm2677 www.national.com 3
all output voltage versions electrical characteristics limits appearing in bold type face apply over the entire junction temperature range of operation, ?40c to 125c. specifications appearing in normal type apply for t a =t j = 25c. unless otherwise specified v in =12v for the 3.3v, 5v and adjustable versions and v in =24v for the 12v version, sync pin open circuited.. symbol parameter conditions typ min max units device parameters i q quiescent current v feedback = 8v 4.2 6 ma for 3.3v, 5.0v, and adj versions v feedback = 15v for 12v versions i stby standby quiescent current on/off pin = 0v 50 100/ 150 a i cl current limit 7 6.1/ 5.75 8.3/ 8.75 a i l output leakage current v in = 40v, on/off pin = 0v v switch =0v 1 200 15 a v switch = ?1v 6 ma r ds(on) switch on-resistance i switch =5a 0.12 0.14/ 0.225 w f o oscillator frequency measured at switch pin 260 225 280 khz d duty cycle maximum duty cycle 91 % minimum duty cycle 0 % i bias feedback bias current v feedback = 1.3v adj version only 85 na v on/off on/off threshold voltage 1.4 0.8 2.0 v i on/off on/off input current on/off input = 0v 20 45 a f sync synchronization frequency v sync (pin 5)=3.5v, 50% duty cycle 400 khz v sync sync threshold voltage 1.4 v q ja thermal resistance t package, junction to ambient 65 (note 5) q ja t package, junction to ambient 45 (note 6) q jc t package, junction to case 2 q ja s package, junction to ambient 56 c/w (note 7) q ja s package, junction to ambient 35 (note 8) q ja s package, junction to ambient 26 (note 9) q jc s package, junction to case 2 ++ note 1: absolute maximum ratings are limits beyond which damage to the device may occur. operating ratings indicate conditions under which of the device is guaranteed. operating ratings do not imply guaranteed performance limits. for guaranteed performance limits and associated test condition, see th e electrical char- acteristics tables. note 2: esd was applied using the human-body model, a 100pf capacitor discharged through a 1.5 k w resistor into each pin. note 3: typical values are determined with t a =t j = 25c and represent the most likely norm. lm2677 www.national.com 4
(continued) note 4: all limits are guaranteed at room temperature (standard type face) and at temperature extremes (bold type face) . all room temperature limits are 100% tested during production with t a =t j = 25c. all limits at temperature extremes are guaranteed via correlation using standard standard quality control (sqc) meth- ods. all limits are used to calculate average outgoing quality level (aoql). note 5: junction to ambient thermal resistance (no external heat sink) for the 7 lead to-220 package mounted vertically, with 1 2 inch leads in a socket, or on a pc board with minimum copper area. note 6: junction to ambient thermal resistance (no external heat sink) for the 7 lead to-220 package mounted vertically, with 1 2 inch leads soldered to a pc board containing approximately 4 square inches of (1 oz.) copper area surrounding the leads. note 7: junction to ambient thermal resistance for the 7 lead to-263 mounted horizontally against a pc board area of 0.136 square inches (the same size as the to-263 package) of 1 oz. (0.0014 in. thick) copper. note 8: junction to ambient thermal resistance for the 7 lead to-263 mounted horizontally against a pc board area of 0.4896 square inches (3.6 times the area of the to-263 package) of 1 oz. (0.0014 in. thick) copper. note 9: junction to ambient thermal resistance for the 7 lead to-263 mounted horizontally against a pc board copper area of 1.0064 square inches (7.4 times the area of the to-263 package) of 1 oz. (0.0014 in. thick) copper. additional copper area will reduce thermal resistance further. see the thermal model in switchers made simple ? software. lm2677 www.national.com 5
typical performance characteristics normalized output voltage ds101301-9 line regulation ds101301-10 efficiency vs input voltage ds101301-11 efficiency vs i load ds101301-12 switch current limit ds101301-4 operating quiescent current ds101301-5 standby quiescent current ds101301-40 on/off threshold voltage ds101301-13 on/off pin current (sourcing) ds101301-14 switching frequency ds101301-15 feedback pin bias current ds101301-16 lm2677 www.national.com 6
block diagram ds101301-6 * active inductor patent number 5,514,947 2 active capacitor patent number 5,382,918 lm2677 www.national.com 7
typical performance characteristics continuous mode switching waveforms v in = 20v, v out =5v,i load =5a l = 10 h, c out = 400 f, c out esr=13m w ds101301-17 a: v sw pin voltage, 10 v/div. b: inductor current, 2 a/div c: output ripple voltage, 20 mv/div ac-coupled horizontal time base: 1 s/div discontinuous mode switching waveforms v in = 20v, v out =5v,i load = 500 ma l = 10 h, c out = 400 f, c out esr=13m w ds101301-18 a: v sw pin voltage, 10 v/div. b: inductor current, 1 a/div c: output ripple voltage, 20 mv/div ac-coupled horizontal time base: 1 s//iv load transient response for continuous mode v in = 20v, v out =5v l = 10 h, c out = 400 f, c out esr=13m w ds101301-19 a: output voltage, 100 mv//div, ac-coupled. b: load current: 500 ma to 5a load pulse horizontal time base: 100 s/div load transient response for discontinuous mode v in = 20v, v out =5v, l = 10 h, c out = 400 f, c out esr=13m w ds101301-20 a: output voltage, 100 mv/div, ac-coupled. b: load current: 200 ma to 5a load pulse horizontal time base: 200 s/div lm2677 www.national.com 8
application hints the lm2677 provides all of the active functions required for a step-down (buck) switching regulator. the internal power switch is a dmos power mosfet to provide power supply designs with high current capability, up to 3a, and highly ef- ficient operation. the lm2677 is part of the simple switcher family of power converters. a complete design uses a minimum num- ber of external components, which have been pre-determined from a variety of manufacturers. using either this data sheet or a design software program called lm267x made simple (version 2.0) a complete switching power sup- ply can be designed quickly. the software is provided free of charge and can be downloaded from national semiconduc- tor's internet site located at http://www.national.com. pin 1 - switch output this is the output of a power mosfet switch connected di- rectly to the input voltage. the switch provides energy to an inductor, an output capacitor and the load circuitry under control of an internal pulse-width-modulator (pwm). the pwm controller is internally clocked by a fixed 260khz oscil- lator. in a standard step-down application the duty cycle (time on/time off) of the power switch is proportional to the ratio of the power supply output voltage to the input volt- age. the voltage on pin 1 switches between vin (switch on) and below ground by the voltage drop of the external schot- tky diode (switch off). pin 2 - input the input voltage for the power supply is connected to pin 2. in addition to providing energy to the load the input voltage also provides bias for the internal circuitry of the lm2677. for guaranteed performance the input voltage must be in the range of 8v to 40v. for best performance of the power sup- ply the input pin should always be bypassed with an input ca- pacitor located close to pin 2. pin3-c boost a capacitor must be connected from pin 3 to the switch out- put, pin 1. this capacitor boosts the gate drive to the internal mosfet above vin to fully turn it on. this minimizes con- duction losses in the power switch to maintain high effi- ciency. the recommended value for c boost is 0.01f. pin 4 - ground this is the ground reference connection for all components in the power supply. in fast-switching, high-current applica- tions such as those implemented with the lm2677, it is rec- ommended that a broad ground plane be used to minimize signal coupling throughout the circuit pin 5 - sync this input allows control of the switching clock frequency. if left open-circuited the regulator will be switched at the inter- nal oscillator frequency, between 225khz and 280khz. an external clock can be used to force the switching frequency and thereby control the output ripple frequency of the regula- tor. this capability provides for consistent filtering of the out- put ripple from system to system as well as precise fre- quency spectrum positioning of the ripple frequency which is often desired in communications and radio applications. this external frequency must be greater than the lm2677 internal oscillator frequency, which could be as high as 280khz, to prevent an erroneous reset of the internal ramp oscillator and pwm control of the power switch. the ramp oscillator is reset on the positive going edge of the sync input signal. it is recommended that the external ttl or cmos compatible clock (between 0v and a level greater than 3v) be ac coupled to the sync input through a 100pf capacitor and a 1k w resistor to ground at pin 5 as shown in figure 1 . pin 6 - feedback this is the input to a two-stage high gain amplifier, which drives the pwm controller. it is necessary to connect pin 6 to the actual output of the power supply to set the dc output voltage. for the fixed output devices (3.3v, 5v and 12v out- puts), a direct wire connection to the output is all that is re- quired as internal gain setting resistors are provided inside the lm2677. for the adjustable output version two external resistors are required to set the dc output voltage. for stable operation of the power supply it is important to prevent cou- pling of any inductor flux to the feedback input. pin 7 - on/off this input provides an electrical on/off control of the power supply. connecting this pin to ground or to any volt- age less than 0.8v will completely turn off the regulator. the current drain from the input supply when off is only 50a. pin 7 has an internal pull-up current source of approxi- mately 20a and a protection clamp zener diode of 7v to ground. when electrically driving the on/off pin the high voltage level for the on condition should not exceed the 6v absolute maximum limit. when on/off control is not re- quired pin 7 should be left open circuited. lm2677 www.national.com 9
application hints (continued) design considerations power supply design using the lm2677 is greatly simplified by using recommended external components. a wide range of inductors, capacitors and schottky diodes from several manufacturers have been evaluated for use in designs that cover the full range of capabilities (input voltage, output volt- age and load current) of the lm2677. a simple design proce- dure using nomographs and component tables provided in this data sheet leads to a working design with very little ef- fort. alternatively, the design software, lm267x made simple (version 2.0), can also be used to provide instant component selection, circuit performance calculations for evaluation, a bill of materials component list and a circuit schematic. the individual components from the various manufacturers called out for use are still just a small sample of the vast ar- ray of components available in the industry. while these components are recommended, they are not exclusively the only components for use in a design. after a close compari- son of component specifications, equivalent devices from other manufacturers could be substituted for use in an appli- cation. important considerations for each external component and an explanation of how the nomographs and selection tables were developed follows. inductor the inductor is the key component in a switching regulator. for efficiency the inductor stores energy during the switch on time and then transfers energy to the load while the switch is off. nomographs are used to select the inductance value re- quired for a given set of operating conditions. the nomo- graphs assume that the circuit is operating in continuous mode (the current flowing through the inductor never falls to zero). the magnitude of inductance is selected to maintain a maximum ripple current of 30% of the maximum load cur- rent. if the ripple current exceeds this 30% limit the next larger value is selected. the inductors offered have been specifically manufactured to provide proper operation under all operating conditions of input and output voltage and load current. several part types are offered for a given amount of inductance. both surface ds101301-7 figure 1. basic circuit for fixed output voltage applications. ds101301-8 figure 2. basic circuit for adjustable output voltage applications lm2677 www.national.com 10
application hints (continued) mount and through-hole devices are available. the inductors from each of the three manufacturers have unique charac- teristics. renco: ferrite stick core inductors; benefits are typically low- est cost and can withstand ripple and transient peak currents above the rated value. these inductors have an external magnetic field, which may generate emi. pulse engineering: powdered iron toroid core inductors; these also can withstand higher than rated currents and, be- ing toroid inductors, will have low emi. coilcraft: ferrite drum core inductors; these are the smallest physical size inductors and are available only as surface mount components. these inductors also generate emi but less than stick inductors. output capacitor the output capacitor acts to smooth the dc output voltage and also provides energy storage. selection of an output ca- pacitor, with an associated equivalent series resistance (esr), impacts both the amount of output ripple voltage and stability of the control loop. the output ripple voltage of the power supply is the product of the capacitor esr and the inductor ripple current. the ca- pacitor types recommended in the tables were selected for having low esr ratings. in addition, both surface mount tantalum capacitors and through-hole aluminum electrolytic capacitors are offered as solutions. impacting frequency stability of the overall control loop, the output capacitance, in conjunction with the inductor, creates a double pole inside the feedback loop. in addition the ca- pacitance and the esr value create a zero. these fre- quency response effects together with the internal frequency compensation circuitry of the lm2677 modify the gain and phase shift of the closed loop system. as a general rule for stable switching regulator circuits it is desired to have the unity gain bandwidth of the circuit to be limited to no more than one-sixth of the controller switching frequency. with the fixed 260khz switching frequency of the lm2677, the output capacitor is selected to provide a unity gain bandwidth of 40khz maximum. each recommended ca- pacitor value has been chosen to achieve this result. in some cases multiple capacitors are required either to re- duce the esr of the output capacitor, to minimize output ripple (a ripple voltage of 1% of vout or less is the assumed performance condition), or to increase the output capaci- tance to reduce the closed loop unity gain bandwidth (to less than 40khz). when parallel combinations of capacitors are required it has been assumed that each capacitor is the ex- act same part type. the rms current and working voltage (wv) ratings of the output capacitor are also important considerations. in a typi- cal step-down switching regulator, the inductor ripple current (set to be no more than 30% of the maximum load current by the inductor selection) is the current that flows through the output capacitor. the capacitor rms current rating must be greater than this ripple current. the voltage rating of the out- put capacitor should be greater than 1.3 times the maximum output voltage of the power supply. if operation of the system at elevated temperatures is required, the capacitor voltage rating may be de-rated to less than the nominal room tem- perature rating. careful inspection of the manufacturer's specification for de-rating of working voltage with tempera- ture is important. input capacitor fast changing currents in high current switching regulators place a significant dynamic load on the unregulated power source. an input capacitor helps to provide additional current to the power supply as well as smooth out input voltage variations. like the output capacitor, the key specifications for the input capacitor are rms current rating and working voltage. the rms current flowing through the input capacitor is equal to one-half of the maximum dc load current so the capacitor should be rated to handle this. paralleling multiple capacitors proportionally increases the current rating of the total capaci- tance. the voltage rating should also be selected to be 1.3 times the maximum input voltage. depending on the unregu- lated input power source, under light load conditions the maximum input voltage could be significantly higher than normal operation and should be considered when selecting an input capacitor. the input capacitor should be placed very close to the input pin of the lm2677. due to relative high current operation with fast transient changes, the series inductance of input connecting wires or pcb traces can create ringing signals at the input terminal which could possibly propagate to the out- put or other parts of the circuitry. it may be necessary in some designs to add a small valued (0.1f to 0.47f) ce- ramic type capacitor in parallel with the input capacitor to prevent or minimize any ringing. catch diode when the power switch in the lm2677 turns off, the current through the inductor continues to flow. the path for this cur- rent is through the diode connected between the switch out- put and ground. this forward biased diode clamps the switch output to a voltage less than ground. this negative voltage must be greater than ?1v so a low voltage drop (particularly at high current levels) schottky diode is recommended. total efficiency of the entire power supply is significantly impacted by the power lost in the output catch diode. the average cur- rent through the catch diode is dependent on the switch duty cycle (d) and is equal to the load current times (1-d). use of a diode rated for much higher current than is required by the actual application helps to minimize the voltage drop and power loss in the diode. during the switch on time the diode will be reversed biased by the input voltage. the reverse voltage rating of the diode should be at least 1.3 times greater than the maximum input voltage. boost capacitor the boost capacitor creates a voltage used to overdrive the gate of the internal power mosfet. this improves efficiency by minimizing the on resistance of the switch and associated power loss. for all applications it is recommended to use a 0.01f/50v ceramic capacitor. sync components when synchronizing the lm2677 with an external clock it is recommended to connect the clock to pin 5 through a series 100pf capacitor and connect a 1k w resistor to ground from pin 5. this rc network creates a short 100ns pulse on each positive edge of the clock to reset the internal ramp oscilla- tor. the reset time of the oscillator is approximately 300ns. lm2677 www.national.com 11
application hints (continued) simple design procedure using the nomographs and tables in this data sheet (or use the available design software at http://www.national.com) a complete step-down regulator can be designed in a few simple steps. step 1: define the power supply operating conditions: required output voltage maximum dc input voltage maximum output load current step 2: set the output voltage by selecting a fixed output lm2677 (3.3v, 5v or 12v applications) or determine the re- quired feedback resistors for use with the adjustable lm2677?adj step 3: determine the inductor required by using one of the four nomographs, figure 3 through figure 6 . table 1 pro- vides a specific manufacturer and part number for the induc- tor. step 4: using table 3 (fixed output voltage) or table 6 (ad- justable output voltage), determine the output capacitance required for stable operation. table 2 provides the specific capacitor type from the manufacturer of choice. step 5: determine an input capacitor from table 4 for fixed output voltage applications. use table 2 to find the specific capacitor type. for adjustable output circuits select a capaci- tor from table 2 with a sufficient working voltage (wv) rating greater than vin max, and an rms current rating greater than one-half the maximum load current (2 or more capacitors in parallel may be required). step 6: select a diode from table 5. the current rating of the diode must be greater than i load max and the reverse volt- age rating must be greater than vin max. step 7: include a 0.01f/50v capacitor for cboost in the de- sign. fixed output voltage design example a system logic power supply bus of 3.3v is to be generated from a wall adapter which provides an unregulated dc volt- age of 13v to 16v. the maximum load current is 2.5a. through-hole components are preferred. step 1: operating conditions are: vout = 3.3v vin max = 16v iload max = 2.5a step 2: select an lm2677t-3.3. the output voltage will have a tolerance of 2% at room temperature and 3% over the full operating temperature range. step 3: use the nomograph for the 3.3v device , figure 3 . the intersection of the 16v horizontal line (v in max) and the 2.5a vertical line (i load max) indicates that l33, a 22h in- ductor, is required. from table 1, l33 in a through-hole component is available from renco with part number rl-1283-22-43 or part number pe-53933 from pulse engineering. step 4: use table 3 to determine an output capacitor. with a 3.3v output and a 22h inductor there are four through-hole output capacitor solutions with the number of same type ca- pacitors to be paralleled and an identifying capacitor code given. table 2 provides the actual capacitor characteristics. any of the following choices will work in the circuit: 1 x 220f/10v sanyo os-con (code c5) 1 x 1000f/35v sanyo mv-gx (code c10) 1 x 2200f/10v nichicon pl (code c5) 1 x 1000f/35v panasonic hfq (code c7) step 5: use table 4 to select an input capacitor. with 3.3v output and 22h there are three through-hole solutions. these capacitors provide a sufficient voltage rating and an rms current rating greater than 1.25a (1/2 i load max). again using table 2 for specific component characteristics the fol- lowing choices are suitable: 1 x 1000f/63v sanyo mv-gx (code c14) 1 x 820f/63v nichicon pl (code c24) 1 x 560f/50v panasonic hfq (code c13) step 6: from tabl e5a3a schottky diode must be selected. for through-hole components 20v rated diodes are sufficient and 2 part types are suitable: 1n5820 sr302 step 7: a 0.01f capacitor will be used for cboost. adjustable output design example in this example it is desired to convert the voltage from a two battery automotive power supply (voltage range of 20v to 28v, typical in large truck applications) to the 14.8vdc alter- nator supply typically used to power electronic equipment from single battery 12v vehicle systems. the load current re- quired is 2a maximum. it is also desired to implement the power supply with all surface mount components. step 1: operating conditions are: vout = 14.8v vin max = 28v iload max = 2a step 2: select an lm2677s-adj. to set the output voltage to 14.9v two resistors need to be chosen (r1 and r2 in fig- ure 2 ). for the adjustable device the output voltage is set by the following relationship: where v fb is the feedback voltage of typically 1.21v. a recommended value to use for r1 is 1k. in this example then r2 is determined to be: r2 = 11.23k w the closest standard 1% tolerance value to use is 11.3k w this will set the nominal output voltage to 14.88v which is within 0.5% of the target value. step 3: to use the nomograph for the adjustable device, fig- ure 6 , requires a calculation of the inductor volt microsecond constant (e t expressed in v s) from the following formula: where v sat is the voltage drop across the internal power switch which is r ds(on) times i load . in this example this would be typically 0.15 w x 2a or 0.3v and v d is the voltage drop across the forward bisased schottky diode, typically 0.5v. the switching frequency of 260khz is the nominal value to use to estimate the on time of the switch during which en- ergy is stored in the inductor. lm2677 www.national.com 12
application hints (continued) for this example e t is found to be: using figure 6 , the intersection of 27v s horizontally and the 2a vertical line (i load max) indicates that l3 8 , a 68h in- ductor, should be used. from table 1, l38 in a surface mount component is available from pulse engineering with part number pe-54038s. step 4: use table 6 to determine an output capacitor. with a 14.8v output the 12.5 to 15v row is used and with a 68h in- ductor there are three surface mount output capacitor solu- tions. table 2 provides the actual capacitor characteristics based on the c code number. any of the following choices can be used: 1 x 33f/20v avx tps (code c6) 1 x 47f/20v sprague 594 (code c8) 1 x 47f/20v kemet t495 (code c8) important note: when using the adjustable device in low voltage applications (less than 3v output), if the nomograph, figure 6, selects an inductance of 22h or less, table 6 does not provide an output capacitor solution. with these condi- tions the number of output capacitors required for stable op- eration becomes impractical. it is recommended to use ei- ther a 33h or 47h inductor and the output capacitors from table 6. step 5: an input capacitor for this example will require at least a 35v wv rating with an rms current rating of 1a (1/2 iout max). from table 2 it can be seen that c12, a 33f/35v capacitor from sprague, has the required voltage/current rat- ing of the surface mount components. step 6: from tabl e5a3a schottky diode must be selected. for surface mount diodes with a margin of safety on the volt- age rating one of five diodes can be used: sk34 30bq040 30wq04f mbrs340 mbrd340 step 7: a 0.01f capacitor will be used for cboost. lm2677 www.national.com 13
application hints (continued) inductor value selection guides (for continuous mode operation) ds101301-21 figure 3. lm2677-3.3 ds101301-22 figure 4. lm2677-5.0 ds101301-23 figure 5. lm2677-12 ds101301-24 figure 6. lm2677-adj lm2677 www.national.com 14
application hints (continued) table 1. inductor manufacturer part numbers inductor reference number inductance (h) current (a) renco pulse engineering coilcraft through hole surface mount through hole surface mount surface mount l23 33 1.35 rl-5471-7 rl1500-33 pe-53823 pe-53823s do3316-333 l24 22 1.65 rl-1283-22-43 rl1500-22 pe-53824 pe-53824s do3316-223 l25 15 2.00 rl-1283-15-43 rl1500-15 pe-53825 pe-53825s do3316-153 l29 100 1.41 rl-5471-4 rl-6050-100 pe-53829 pe-53829s do5022p-104 l30 68 1.71 rl-5471-5 rl6050-68 pe-53830 pe-53830s do5022p-683 l31 47 2.06 rl-5471-6 rl6050-47 pe-53831 pe-53831s do5022p-473 l32 33 2.46 rl-5471-7 rl6050-33 pe-53932 pe-53932s do5022p-333 l33 22 3.02 rl-1283-22-43 rl6050-22 pe-53933 pe-53933s do5022p-223 l34 15 3.65 rl-1283-15-43 e pe-53934 pe-53934s do5022p-153 l38 68 2.97 rl-5472-2 e pe-54038 pe-54038s e l39 47 3.57 rl-5472-3 e pe-54039 pe-54039s e l40 33 4.26 rl-1283-33-43 e pe-54040 pe-54040s e l41 22 5.22 rl-1283-22-43 e pe-54041 p0841 e l44 68 3.45 rl-5473-3 e pe-54044 e e l45 10 4.47 rl-1283-10-43 e e p0845 do5022p-103hc l46 15 5.60 rl-1283-15-43 e e p0846 do5022p-153hc l47 10 5.66 rl-1283-10-43 e e p0847 do5022p-103hc l48 47 5.61 rl-1282-47-43 e e p0848 e l49 33 5.61 rl-1282-33-43 e e p0849 e inductor manufacturer contact numbers coilcraft phone (800) 322-2645 fax (708) 639-1469 coilcraft, europe phone +44 1236 730 595 fax +44 1236 730 627 pulse engineering phone (619) 674-8100 fax (619) 674-8262 pulse engineering, phone +353 93 24 107 europe fax +353 93 24 459 renco electronics phone (800) 645-5828 fax (516) 586-5562 lm2677 www.national.com 15
application hints (continued) table 2. input and output capacitor codes capacitor reference code surface mount avx tps series sprague 594d series kemet t495 series c (f) wv (v) irms (a) c (f) wv (v) irms (a) c (f) wv (v) irms (a) c1 330 6.3 1.15 120 6.3 1.1 100 6.3 0.82 c2 100 10 1.1 220 6.3 1.4 220 6.3 1.1 c3 220 10 1.15 68 10 1.05 330 6.3 1.1 c4 47 16 0.89 150 10 1.35 100 10 1.1 c5 100 16 1.15 47 16 1 150 10 1.1 c6 33 20 0.77 100 16 1.3 220 10 1.1 c7 68 20 0.94 180 16 1.95 33 20 0.78 c8 22 25 0.77 47 20 1.15 47 20 0.94 c9 10 35 0.63 33 25 1.05 68 20 0.94 c10 22 35 0.66 68 25 1.6 10 35 0.63 c11 15 35 0.75 22 35 0.63 c12 33 35 1 4.7 50 0.66 c13 15 50 0.9 lm2677 www.national.com 16
application hints (continued) input and output capacitor codes (continued) capacitor reference code through hole sanyo os-con sa series sanyo mv-gx series nichicon pl series panasonic hfq series c (f) wv (v) irms (a) c (f) wv (v) irms (a) c (f) wv (v) irms (a) c (f) wv (v) irms (a) c1 47 6.3 1 1000 6.3 0.8 680 10 0.8 82 35 0.4 c2 150 6.3 1.95 270 16 0.6 820 10 0.98 120 35 0.44 c3 330 6.3 2.45 470 16 0.75 1000 10 1.06 220 35 0.76 c4 100 10 1.87 560 16 0.95 1200 10 1.28 330 35 1.01 c5 220 10 2.36 820 16 1.25 2200 10 1.71 560 35 1.4 c6 33 16 0.96 1000 16 1.3 3300 10 2.18 820 35 1.62 c7 100 16 1.92 150 35 0.65 3900 10 2.36 1000 35 1.73 c8 150 16 2.28 470 35 1.3 6800 10 2.68 2200 35 2.8 c9 100 20 2.25 680 35 1.4 180 16 0.41 56 50 0.36 c10 47 25 2.09 1000 35 1.7 270 16 0.55 100 50 0.5 c11 220 63 0.76 470 16 0.77 220 50 0.92 c12 470 63 1.2 680 16 1.02 470 50 1.44 c13 680 63 1.5 820 16 1.22 560 50 1.68 c14 1000 63 1.75 1800 16 1.88 1200 50 2.22 c15 220 25 0.63 330 63 1.42 c16 220 35 0.79 1500 63 2.51 c17 560 35 1.43 c18 2200 35 2.68 c19 150 50 0.82 c20 220 50 1.04 c21 330 50 1.3 c22 100 63 0.75 c23 390 63 1.62 c24 820 63 2.22 c25 1200 63 2.51 capacitor manufacturer contact numbers nichicon phone (847) 843-7500 fax (847) 843-2798 panasonic phone (714) 373-7857 fax (714) 373-7102 avx phone (845) 448-9411 fax (845) 448-1943 sprague/vishay phone (207) 324-4140 fax (207) 324-7223 sanyo phone (619) 661-6322 fax (619) 661-1055 kemet phone (864) 963-6300 fax (864) 963-6521 lm2677 www.national.com 17
application hints (continued) table 3. output capacitors for fixed output voltage application output voltage (v) inductance (h) surface mount avx tps series sprague 594d series kemet t495 series no. c code no. c code no. c code 3.3 10 5c15c15c2 15 4c14c14c3 22 3c22c73c4 33 1c12c73c4 5 10 4c24c64c4 15 3c32c73c5 22 3c22c73c4 33 2c22c32c4 47 2c21c72c4 12 10 4c53c65c9 15 3c52c74c9 22 2c52c63c8 33 2c51c73c8 47 2c41c62c8 68 1c51c52c7 100 1c41c51c8 output voltage (v) inductance (h) through hole sanyo os-con sa series sanyo mv-gx series nichicon pl series panasonic hfq series no. c code no. c code no. c code no. c code 3.3 10 2 c5 2 c6 1 c8 2 c6 15 2 c5 2 c5 1 c7 2 c5 22 1 c5 1 c10 1 c5 1 c7 33 1 c5 1 c10 1 c5 1 c7 5 10 2 c4 2 c5 1 c6 2 c5 15 1 c5 1 c10 1 c5 1 c7 22 1 c5 1 c9 1 c5 1 c5 33 1 c4 1 c5 1 c4 1 c4 47 1 c4 1 c4 1 c2 2 c4 12 10 2 c7 1 c10 1 c14 2 c4 15 1 c8 1 c6 1 c17 1 c5 22 1 c7 1 c5 1 c13 1 c5 33 1 c7 1 c4 1 c12 1 c4 47 1 c7 1 c3 1 c11 1 c3 68 1 c6 1 c2 1 c10 1 c3 100 1 c6 1 c2 1 c9 1 c1 no. represents the number of identical capacitor types to be connected in parallel c code indicates the capacitor reference number in table 2 for identifying the specific component from the manufacturer. lm2677 www.national.com 18
application hints (continued) table 4. input capacitors for fixed output voltage application (assumes worst case maximum input voltage and load current for a given inductance value) output voltage (v) inductance (h) surface mount avx tps series sprague 594d series kemet t495 series no. c code no. c code no. c code 3.3 10 3c72c103c9 15 ** 3 c13 4 c12 22 ** 2 c13 3 c12 33 ** 2 c13 3 c12 5 10 3c42c63c9 15 4 c9 3 c12 4 c10 22 ** 3 c13 4 c12 33 ** 2 c13 3 c12 47 ** 1 c13 2 c12 12 10 4 c9 2 c10 4 c10 15 4 c8 2 c10 4 c10 22 4 c9 3 c12 4 c10 33 ** 3 c13 4 c12 47 ** 2 c13 3 c12 68 ** 2 c13 2 c12 100 ** 1 c13 2 c12 output voltage (v) inductance (h) through hole sanyo os-con sa series sanyo mv-gx series nichicon pl series panasonic hfq series no. c code no. c code no. c code no. c code 3.3 10 2 c9 2 c8 1 c18 1 c8 15 ** 2 c13 1 c25 1 c16 22 ** 1 c14 1 c24 1 c16 33 ** 1 c14 1 c24 1 c16 5 10 2 c7 2 c8 1 c25 1 c8 15 ** 2c81c251c8 22 ** 2 c13 1 c25 1 c16 33 ** 1 c14 1 c23 1 c13 47 ** 1 c12 1 c19 1 c11 12 10 2 c10 2 c8 1 c18 1 c8 15 2 c10 2 c8 1 c18 1 c8 22 ** 2c81c181c8 33 ** 2 c12 1 c24 1 c14 47 ** 1 c14 1 c23 1 c13 68 ** 1 c13 1 c21 1 c15 100 ** 1 c11 1 c22 1 c11 * check voltage rating of capacitors to be greater than application input voltage. no. represents the number of identical capacitor types to be connected in parallel c code indicates the capacitor reference number in table 2 for identifying the specific component from the manufacturer. lm2677 www.national.com 19
application hints (continued) table 5. schottky diode selection table reverse voltage (v) surface mount through hole 3a 5a or more 3a 5a or more 20v sk32 1n5820 sr302 30v sk33 mbrd835l 1n5821 30wq03f 31dq03 40v sk34 mbrb1545ct 1n5822 30bq040 6tq045s mbr340 mbr745 30wq04f 31dq04 80sq045 mbrs340 sr403 6tq045 mbrd340 50v or more sk35 mbr350 30wq05f 31dq05 sr305 diode manufacturer contact numbers international rectifier phone (310) 322-3331 fax (310) 322-3332 motorola phone (800) 521-6274 fax (602) 244-6609 general semiconductor phone (516) 847-3000 fax (516) 847-3236 diodes, inc. phone (805) 446-4800 fax (805) 446-4850 lm2677 www.national.com 20
application hints (continued) table 6. output capacitors for adjustable output voltage applications output voltage (v) inductance (h) surface mount avx tps series sprague 594d series kemet t495 series no. c code no. c code no. c code 1.21 to 2.50 33 * 7c16c27c3 47 * 5c14c25c3 2.5 to 3.75 33 * 4c13c24c3 47 * 3c12c23c3 3.75 to 5 22 4c13c24c3 33 3c12c23c3 47 2c12c22c3 5 to 6.25 22 3c21c33c4 33 2c22c32c4 47 2c22c32c4 68 1c21c31c4 6.25 to 7.5 22 3c21c43c4 33 2c21c32c4 47 1c31c41c6 68 1c21c31c4 7.5 to 10 33 2c51c62c8 47 1c51c62c8 68 1c51c61c8 100 1c41c51c8 10 to 12.5 33 1c51c62c8 47 1c51c62c8 68 1c51c61c8 100 1c51c61c8 12.5 to 15 33 1c61c81c8 47 1c61c81c8 68 1c61c81c8 100 1c61c81c8 15 to 20 33 1 c8 1 c10 2 c10 47 1c81c92c10 68 1c81c92c10 100 1c81c91c10 20 to 30 33 2 c9 2 c11 2 c11 47 1 c10 1 c12 1 c11 68 1 c9 1 c12 1 c11 100 1 c9 1 c12 1 c11 30 to 37 10 4 c13 8 c12 15 3 c13 5 c12 22 no values available 2 c13 4 c12 33 1 c13 3 c12 47 1 c13 2 c12 68 1 c13 2 c12 lm2677 www.national.com 21
application hints (continued) output capacitors for adjustable output voltage applications (continued) output voltage (v) inductance (h) through hole sanyo os-con sa series sanyo mv-gx series nichicon pl series panasonic hfq series no. c code no. c code no. c code no. c code 1.21 to 2.50 33 * 2c35c15c33 c 47 * 2c24c13c32c5 2.5 to 3.75 33 * 1c33c13c12c5 47 * 1c22c12c31c5 3.75 to 5 22 1 c3 3 c1 3 c1 2 c5 33 1 c2 2 c1 2 c1 1 c5 47 1 c2 2 c1 1 c3 1 c5 5 to 6.25 22 1 c5 2 c6 2 c3 2 c5 33 1 c4 1 c6 2 c1 1 c5 47 1 c4 1 c6 1 c3 1 c5 68 1 c4 1 c6 1 c1 1 c5 6.25 to 7.5 22 1 c5 1 c6 2 c1 1 c5 33 1 c4 1 c6 1 c3 1 c5 47 1 c4 1 c6 1 c1 1 c5 68 1 c4 1 c2 1 c1 1 c5 7.5 to 10 33 1 c7 1 c6 1 c14 1 c5 47 1 c7 1 c6 1 c14 1 c5 68 1 c7 1 c2 1 c14 1 c2 100 1 c7 1 c2 1 c14 1 c2 10 to 12.5 33 1 c7 1 c6 1 c14 1 c5 47 1 c7 1 c2 1 c14 1 c5 68 1 c7 1 c2 1 c9 1 c2 100 1 c7 1 c2 1 c9 1 c2 12.5 to 15 33 1 c9 1 c10 1 c15 1 c2 47 1 c9 1 c10 1 c15 1 c2 68 1 c9 1 c10 1 c15 1 c2 100 1 c9 1 c10 1 c15 1 c2 15 to 20 33 1 c10 1 c7 1 c15 1 c2 47 1 c10 1 c7 1 c15 1 c2 68 1 c10 1 c7 1 c15 1 c2 100 1 c10 1 c7 1 c15 1 c2 20 to 30 33 1 c7 1 c16 1 c2 47 no values 1 c7 1 c16 1 c2 68 available 1 c7 1 c16 1 c2 100 1 c7 1 c16 1 c2 30 to 37 10 1 c12 1 c20 1 c10 15 1 c11 1 c20 1 c11 22 no values 1 c11 1 c20 1 c10 33 available 1 c11 1 c20 1 c10 47 1 c11 1 c20 1 c10 68 1 c11 1 c20 1 c10 * set to a higher value for a practical design solution. see applications hints section no. represents the number of identical capacitor types to be connected in parallel c code indicates the capacitor reference number in table 2 for identifying the specific component from the manufacturer. lm2677 www.national.com 22
physical dimensions inches (millimeters) unless otherwise noted to-263 surface mount power package order number lm2677s-3.3, lm2677s-5.0, lm2677s-12 or lm2677s-adj ns package number ts7b lm2677 www.national.com 23
physical dimensions inches (millimeters) unless otherwise noted (continued) life support policy national's products are not authorized for use as critical components in life support devices or systems without the express written approval of the president and general counsel of national semiconductor corporation. as used herein: 1. life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. a critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. national semiconductor corporation americas tel: 1-800-272-9959 fax: 1-800-737-7018 email: support@nsc.com national semiconductor europe fax: +49 (0) 180-530 85 86 email: europe.support@nsc.com deutsch tel: +49 (0) 69 9508 6208 english tel: +44 (0) 870 24 0 2171 fran?ais tel: +33 (0) 1 41 91 8790 national semiconductor asia pacific customer response group tel: 65-2544466 fax: 65-2504466 email: ap.support@nsc.com national semiconductor japan ltd. tel: 81-3-5639-7560 fax: 81-3-5639-7507 www.national.com to-220 power package order number lm2677t-3.3, lm2677t-5.0, lm2677t-12 or lm2677t-adj ns package number ta07b lm2677 simple switcher high efficiency 5a step-down voltage regulator with sync national does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and national reserves the righ t at any time without notice to change said circuitry and specifications.

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