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? semiconductor components industries, llc, 2006 october, 2006 ? rev. 5 1 publication order number: ncp1423/d ncp1423 400 ma sync?rect pfm step?up dc?dc converter with true?cutoff and ring?killer ncp1423 is a monolithic micropow er high frequency step?up switching converter ic specially designed for battery operated hand?held electronic products. it in tegrates synchronous rectifier for improving efficiency as well as eliminating the external schottky diode. high switching frequency (up to 600 khz) allows low profile inductor and output capacitor being used. when the ic is disabled, internal conduction path from lx or bat to out is blocked, out pin is isolated from the battery. this achieves true?cutoff. ring?killer is also integrated to eliminate the high frequency ringing in discontinuous conduction mode. low?battery detector, cycle?by?cycle current limit, overvoltage protection and thermal shutdown provide value?added features for various battery operated application. with all of these functions on, the quiescent supply current is only 9.0 a. this device is available in compact micro10 package. features ? high efficiency: 92% for 3.3 v output@ 400 ma from 2.5 v input 87% for 1.8 v output@ 70 ma from 1.2 v input ? high switching frequency, up to 600 khz (not hitting current limit) ? low quiescent current of 9.0 a ? low battery detector ? 0.8 v startup ? external adjustable output voltage ? 1.5% output voltage accuracy ? ring?killer for discontinuous conduction mode ? thermal shutdown ? 1.2 a cycle?by?cycle current limit ? output current up to 400 ma @ v out = 3.3 v, 200 ma @ v out = 1.8 v ? overvoltage protection ? low profile and minimum external part ? open drain low?battery detector output ? compact micro10 package ? pb?free package is available typical applications ? wireless optical mouse ? wireless headsets ? internet audio players ? personal digital assistants (pdas) ? hand?held instruments ? conversion from one/two nimh or nicd cells to 1.8 v / 3.3 v pin connections device package shipping ? ordering information ncp1423dmr2 micro10 4000 tape & reel http://onsemi.com marking diagram dar = device code a = assembly location y = year w = work week = pb?free package (top view) micro10 dm suffix case 846b en lbo ref fb out lbi aden bat gnd lx 1 2 3 4 5 10 9 8 7 6 micro10 ?for information on tape and reel specifications, including part orientation and tape sizes, please refer to our t ape and reel packaging specification s brochure, brd8011/d. dar ayw NCP1423DMR2G micro10 (pb?free) 4000 tape & reel (note: microdot may be in either location)
ncp1423 http://onsemi.com 2 figure 1. typical operation circuit en ref fb gnd out bat lx aden lbi lbo off on off on r1 r2 100k 5.6 h 10 f c in 22 f c out 0.1 f * optional * low battery open drain output low battery sense input ncp1423 r4 r3 c1 pin description pin no. symbol description 1 en low?battery detector input and enable. with this pin pulled down below 0.5 v, the device will be disabled and will enter shutdown mode 2 ref 1.195 v reference voltage output, bypass with 0.1 f capacitor if this pin is not loaded, with a 1.0 f bypassing capacitor, this pin can be loaded up to 2.5 ma @ v out = 3.3 v. 3 fb output voltage feedback input 4 gnd ground 5 out power output. out provides bootstrap power to the ic 6 bat battery supply input pin and connection for internal ring?killer 7 lx n?channel and p?channel power mosfet drain 8 aden auto discharge input 9 lbi low?battery detector input 10 lbo open?drain low?battery detector output. output is low when v lbi is < 500 mv. lbo is high impedance shutdown maximum ratings rating symbol value unit power supply (pin 6) v out ?0.3, 6.0 v input / output pins (pins 1?3,5,7?10) v io ?0.3, 6.0 v thermal characteristics micro10 plastic package, case 846b, t a = 25 c thermal resistance junction?to?air p d r ja 480 250 mw c/w operating junction temperature range t j ? 40 to + 150 c operating ambient temperature range t a ? 40 to + 85 c storage temperature range t stg ? 55 to +150 c stresses exceeding maximum ratings may damage the device. maximum ratings are stress ratings only. functional operation above t he recommended operating conditions is not implied. extended exposure to stresses above the recommended operating conditions may af fect device reliability. note: esd data available upon request. 1. this device contains esd protection and exceeds the following tests: human body model (hbm) 2.0 kv per jedec standard: jesd22?a114. machine model (mm) 200 v per jedec standard: jesd22?a115. 2. the maximum package power dissipation limit must not be exceeded. p d t j(max) t a r ja 3. latchup current maximum rating: 150 ma per jedec standard: jesd78. 4. moisture sensitivity level: msl 1 per ipc/jedec standard: j?std?020a. 5. measured on approximately 1 in sq of 1 oz cu.
ncp1423 http://onsemi.com 3 electrical characteristics (v out = 3.3 v, t a = 25 c for typical value, ?40 c t a 85 c for min/max values unless otherwise noted.) characteristic symbol min typ max unit operating voltage v in 0.8 ? v out v output voltage range v out 1.8 ? 3.3 v minimum input voltage for startup v in_min ? 0.85 0.90 v reference voltage (i load = 0 ma, cref = 100 nf, t a = 25 c) v ref 1.177 1.195 1.213 v reference voltage temperature coefficient tc vref ? 0.05 ? mv/ c fb input threshold (i load = 0 ma, t a = ?40 c to 85 c) v fb 0.489 0.500 0.512 v fb input threshold (i load = 0 ma, t a = 25 c) v fb 0.493 0.500 0.508 v fb input current i fb ? 1.0 ? na internal nfet on?resistance (i lx =100 ma, t a = 25 c) (note 7) r ds(on)_n ? 0.3 0.45 internal pfet on?resistance (i lx =100 ma, t a = 25 c) (note 7) r ds(on)_p ? 0.6 0.8 lx switch current limit (nfet) (note 7) i lim ? 1.2 ? a operating current into out (v fb = 0.7 v, t a = 25 c) i q ? 9.0 12 a operating current into bat (v bat = 1.2 v, v fb = 0.7 v, v lx = 1.2 v, t a = 25 c) i qbat ? 2.0 3.0 a shutdown current into bat (lbi/en = 0 v, v bat = 3.3 v, t a = 25 c) i bat_sd ? 0.5 1.5 a lx switch max. on?time (v fb = 0 v) t on 1.15 1.4 2.8 s lx switch min. off?time (v fb = 0 v) t off 80 200 350 ns bat to lx resistance (v fb = 0.7 v) r bat_lx ? 100 ? lbi input threshold v lbi 0.475 0.500 0.525 v lbi input hysteresis v lbi_hys ? 15 ? mv lbi input current i lbi ? 1.5 ? na lbo low output voltage (v lbi = 0 v, i sink = 1.0 ma) v lbo_l ? ? 0.2 v maximum continuous output current (v in = 2.5 v, v out = 3.3 v) (note 7) i out 200 ? ? ma maximum continuous output current (v in = 0.8 v, v out = 3.3 v) (note 7) i out 100 ? ? ma soft start time (v in = 1.2 v, t a = 25 c, c ref = 100 nf, v out = 3.3 v) (note 6) t ss ? 2.0 8.0 ms en shutdown threshold (v bat = 1.2 v) v shdn 0.34 0.50 0.68 v en input current i en ? 150 ? na aden threshold (v bat = 0.9 v to 3.3 v) v aden 0.5*v bat v aden input current i aden ? 100 ? na aden switch resistance r aden 100 thermal shutdown temperature (note 7) t shdn ? ? 145 c thermal shutdown hysteresis (note 7) t sdhys ? 30 ? c 6. value depends on voltage at v out . 7. values are guaranteed by design.
ncp1423 http://onsemi.com 4 chip enable figure 2. detailed block diagram _zcur _mson _cen _pfm _tsdon _mainsw2on _mainswofd _synsw2on _synswofd _v refok control logic 20 mv + ? pfm voltage reference lbi 9 + ? fb 3 + ? zlc + true cutoff control v dd gnd v dd gnd + ? + gnd r sense gnd sensefet ? m1 v dd m3 bat 6 lx 7 out 5 v bat 4 gnd v out lbo 10 _ilim 0.5 v 0.5 v m2 en 1 aden 8 gnd ref 2 1.2 v
ncp1423 http://onsemi.com 5 typical operating characteristics 1.180 1.185 1.190 1.195 1.200 1.210 0.0 0.2 0.4 0.6 0.8 1.0 ?40 ?20 0 20 40 60 80 10 0 t a , ambient temperature, ( c) r ds(on) , switch on resistance ( p?fet (m2) n?fet (m1) v out = 3.3 v ?50 ?25 0 25 50 75 100 t a , ambient temperature ( c) v ref , reference voltage (v) 0.44 0.46 0.48 0.50 0.52 0.54 ?50 ?25 0 25 50 75 100 0 3 6 9 12 ?50 0 25 50 75 10 0 t a , ambient temperature ( c) i q , operation current ( a) figure 3. reference voltage vs. output current figure 4. reference voltage vs. voltage at out pi n figure 5. reference voltage vs. temperature figure 6. switch on resistance vs. temperature figure 7. low battery detect voltage vs. temperature figure 8. operation current vs. temperature 1.15 1.17 1.19 1.21 1.23 1 10 100 1000 c ref = 0.1 f v in = 1.2 v v out = 3.3 v t a = 25 c t a , ambient temperature ( c) v lbi , low battery detect voltage (v) i load , output current (ma) v ref , reference voltage (v) 1.13 1.15 1.23 1.25 c ref = 0.1 f i ref = 0 ma t a = 25 c v out , voltage at out pin, (v) v ref , reference voltage (v) v out = 3.3 v c ref = 0.1 f i ref = 0 ma 1.5 2 2.5 3 3.5 4 4.5 5 1.17 1.25 1.27 1.19 1.21 1.205 0.56 t a = 25 c v out = 3.3 v ?25 15 18
ncp1423 http://onsemi.com 6 typical operating characteristics 0.8 1.0 1.2 1.4 1.6 2.0 ?50 ?25 0 25 50 75 100 figure 9. lbi input current vs. temperature figure 10. shutdown current vs. temperature figure 11. aden pin input current vs. temperature figure 12. feedback threshold voltage vs. temperature figure 13. l x switch maximum on time vs. temperature figure 14. l x switch minimum off time vs. temperature t a , ambient temperature ( c) t on , l x switch maximum on time ( s) 0 1 2 3 4 ?50 0 25 50 75 100 t a , ambient temperature ( c) i lbi , lbi input current (na) v out = 3.3 v ?25 5 6 0.0 2.5 5.0 7.5 10.0 ?50 0 25 50 75 10 0 t a , ambient temperature ( c) i bat_sd , shutdown current ( a) v out = 3.3 v ?25 12.5 15.0 25 50 75 100 125 ?50 0 25 50 75 100 t a , ambient temperature ( c) i aden , aden pin input current (na) ?25 150 175 0.47 0.48 0.49 0.50 0.51 ?50 0 25 50 75 10 0 t a , ambient temperature ( c) v fb , feedback threshold voltage (v) v out = 3.3 v ?25 0.52 0.53 1.8 v out = 3.3 v 0.14 0.16 0.18 0.20 0.22 0.26 ?50 ?25 025507510 0 t a , ambient temperature ( c) t off , l x switch minimum off time ( s) 0.24 v out = 3.3 v
ncp1423 http://onsemi.com 7 typical operating characteristics 40 50 60 70 80 90 100 1 10 100 1000 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0 50 100 150 200 250 figure 15. en input current vs. temperature figure 16. minimum startup battery voltage vs. loading current figure 17. output voltage change vs. load current figure 18. output voltage change vs. load current figure 19. efficiency vs. load current figure 20. efficiency vs. load current i load , output loading current (ma) v batt , minimum startup battery voltage (v) 0 50 100 150 200 ?50 0 25 50 75 100 t a , ambient temperature ( c) i en , en pin input current (na) v out = 3.3 v ?25 250 300 t a = 25 c v out = 3.3 v l = 5.6 h c in = 10 f c out = 22 f v out > 0.9 x v set 50 60 70 80 90 100 1 10 100 1000 v out = 3.3 v c in = 10 f, c out = 22 f l = 5.6 h, t a = 25 c v in = 1.2 v, 1.5 v, 2.0 v, 2.5 v i load , output loading current (ma) efficiency (%) ?6 ?4 ?2 0 2 6 1 10 100 1000 v out = 3.3 v, l = 5.6 h c in = 10 f, c out = 22 f t a = 25 c i load , output loading current (ma) output voltage change (%) 1.5 v v in = 2.5 v v in = 2.5 v v in = 1.2 v 4 1.0 v ?6 ?4 ?2 0 2 6 1 10 100 1000 v out = 1.8 v, l = 5.6 h c in = 10 f, c out = 22 f t a = 25 c i load , output loading current (ma) output voltage change (%) 1.2 v v in = 1.5 v 4 1.0 v 2.0 v 1.5 v v out = 1.8 v c in = 10 f, c out = 22 f l = 5.6 h, t a = 25 c v in = 1.0 v, 1.2 v, 1.5 v i load , output loading current (ma) efficiency (%) v in = 1.5 v 1.2 v 1.0 v
ncp1423 http://onsemi.com 8 typical operating characteristics 0 50 100 150 200 250 1.3 1.7 1.9 2.1 2.3 2.5 figure 21. output ripple voltage vs. battery input voltage figure 22. no load operating current vs. inpu t voltage at out pin figure 23. low battery detect figure 24. startup transient response v batt , battery input voltage (v) v ripple , output ripple voltage (mv p?p ) 100 ma 50 ma v out = 3.3 v, l = 5.6 h c in = 10 f, c out = 22 f t a = 25 c upper trace: output voltage waveform, 2.0 v/division middle trace: input voltage waveform, 1.0 v/division lower trace: inductor current waveform, 500 ma/divisio n (v in = 1.8 v, v out = 3.3 v, l = 5.6 h, i load = 60 ma) 2.5 5.0 7.5 10 12.5 15 1.8 2.1 2.4 2.7 3.0 v out , input voltage at out pin (v) i batt , no load operating current ( a ) 3 .3 upper trace: voltage at lbi pin, 0.5 v/division lower trace: voltage at lbo pin, 1.0 v/division upper trace: output voltage ripple, 100 mv/division middle trace: voltage at lx pin, 2.0 v/division lower trace: inductor current, 500 ma/division (v in = 1.5 v, v out = 3.3 v, i load = 50 ma; l = 5.6 h, c out = 22 f) figure 25. discontinuous conduction mode switching waveform upper trace: output v oltage ripple, 100 mv/division middle trace: voltage at lx pin, 2.0 v/division lower trace: inductor current, 500 ma/division (v in = 1.5 v, v out = 3.3 v, i load = 200 ma; l = 5.6 h, c out = 22 f ) figure 26. continuous conduction mode switching waveform 1.5 l = 5.6 h, c in = 10 f, c out = 22 f, t a = 25 c
ncp1423 http://onsemi.com 9 typical operating characteristics figure 27. line transient response for v out = 3.3 v figure 28. line transient response for v out = 1.8 v upper trace: output voltage ripple, 50 mv/division lower trace: battery voltage, v in, 1.0 v/division (v in = 1.2 v to 2.0 v; l = 5.6 h, c out = 22 f, i load = 50 ma) upper trace: output voltage ripple, 50 mv/division lower trace: battery voltage, v in, 1.0 v/division (v in = 1.0 v to 1.6 v; l = 5.6 h, c out = 22 f, i load = 50 ma) figure 29. load transient response for v in = 1.5 v figure 30. load transient response for v in = 1.0 v upper trace: output v oltage ripple, 100 mv/division lower trace: load current, i load , 100 ma/division (v out = 1.8 v, i load = 10 ma to 100 ma; l = 5.6 h, c out = 22 f) upper trace: output voltage ripple, 100 mv/division lower trace: load current, i load , 100 ma/division (v out = 3.3 v, i load = 10 ma to 200 ma; l = 5.6 h, c out = 22 f) figure 31. startup waveform (aden disabled) figure 32. startup waveform (aden enabled) upper trace: output voltage, 2.0 v/division lower trace: output current, 50 ma/division middle trace: enable pin waveform, 1.0 v/division (v in = 1.5 v, v out = 3.3 v, l = 5.6 h, c in = 10 f, c out = 22 f) upper trace: output voltage, 2.0 v/division lower trace: output current, 50 ma/division middle trace: enable pin waveform, 1.0 v/division (v in = 1.5 v, v out = 3.3 v, l = 5.6 h, c in = 10 f, c out = 22 f)
ncp1423 http://onsemi.com 10 detailed operation description ncp1423 is a monolithic micropower high?frequency step?up voltage switching converter ic specially designed for battery operated hand?held electronic products up to 200 ma loading. it integrates a synchronous rectifier to improving efficiency as well as to eliminate the external schottky diode. high switching frequency (up to 600 khz) allows for a low profile inductor and output capacitor to be used. low?battery detector, logic?controlled shutdown and cycle?by?cycle current limit provide value?added features for various battery?operated applications. with all these functions on, the quiescent supply current is typical only 9 a typical. this device is available in compact micro10 package. pfm regulation scheme from the detailed block diagram (figure 2), the output voltage is divided down and fed back to pin 3 (fb). this voltage goes to the non?inverting input of the pfm comparator whereas the comparator?s inverting input is connected to the internal voltage reference, ref. a switching cycle is initiated by the falling edge of the comparator, at the moment the main switch (m1) is turned on. after the maximum on?time (typical 1.4 s) elapses or the current limit is reached, m1 is turned off, and the synchronous switch (m2) is turned on. the m1 off time is not less than the minimum off?time (typically 0.20 s), which ensure complete energy transfer from the inductor to the output capacitor. if the regulator is operating in continuous conduction mode (ccm), m2 is turned off just before m1 is supposed to be on again. if the regulator is operating in discontinuous conduction mode (dcm), which means the coil current will decrease to zero before the new cycle start, m1 is turned off as the coil current is almost reaching zero. the comparator (zlc) with fixed offset is dedicated to sense the voltage drop across m2 as it is conducting, when the voltage drop is below the offset, the zlc comparator output goes high, and m2 is turned off. negative feedback of closed loop operation regulates voltage at pin 3 (fb) equal to the internal divide down reference voltage times (0.5 v). synchronous rectification the synchronous rectifier is used to replace the schottky diode to reduce the conduction loss contributed by the forward voltage of the schottky diode. the synchronous rectifier is normally realized by powerfet with gate control circuitry that incorporates relatively complicated timing concerns. as the main switch (m1) is being turned off and the synchronous switch m2 is just turned on with m1 not being completely turned off, current is shunt from the output bulk capacitor through m2 and m1 to ground. this power loss lowers overall ef ficiency and possibly damage the switching fets. as a general practice, certain amount of dead time is introduced to make sure m1 is completely turned off before m2 is being turned on. the previously mentioned situation occurs when the regulator is operating in ccm, m2 is being turned off, m1 is just turned on, and m2 is not being completely turned off, a dead time is also needed to make sure m2 is completely turned off before m1 is being turned on. as coil current is dropped to zero when the regulator is operating in dcm, m2 should be off. if this does not occur, the reverse current flows from the output bulk capacitor through m2 and the inductor to the battery input, causing damage to the battery. the zlc comparator comes with fixed offset voltage to switch m2 off before any reverse current builds up. however, if m2 switch off too early, large residue coil current flows through the body diode of m2 and increases conduction loss. therefore, determination on the offset voltage is essential for optimum performance. with the implementation of synchronous rectification scheme, efficiency can be as high as 90% with this device. cycle?by?cycle current limit in figure 2, sensefet is used to sample the coil current as m1 is on. with that sample current flowing through a sense resistor, a sense?voltage is developed. threshold detector (i lim ) detects whether the sense?voltage is higher than the preset level. if the sense voltage is higher than the present level, t he detector output notifies the control logic to switch off m1, and m1 can only be switched on when the next cycle starts after the minimum off?time (typically 0.20 s). with proper sizing of sensefet and sense resistor, the peak coil current limit is typically set at 1.2 a. voltage reference the voltage at ref is typically set at 1.2 v and can output up to 2.5 ma with load regulation 2.0%, at v out equal to 3.3 v. if v out is increased, the ref load capability can also be increased. a bypass capacitor of 200 nf is required for proper operation when ref is not loaded. if ref is loaded, 1.0 f capacitor at ref pin is needed. true?cutoff the ncp1423 has a true?cutoff function controlled by the en pin (pin 1). internal circuitry can isolate the current through the body diode of switch m2 to load. thus, it can eliminate leakage current from the battery to load in shutdown mode and significantly reduces battery current consumption during shutdown. the shutdown function is controlled by the voltage at pin 1 (en). when pin 1 is pulled to lower than 0.5 v, the controller enters shutdown mode. in shutdown mode, when the switches m1 and m2 are both switched off, the internal reference voltage of the controller is disable and the controller typically consumes only 600 na of current. if the pin 1 voltage is raised to higher than 0.5 v, for example, by a resistor connected to v in , the
ncp1423 http://onsemi.com 11 ic is enabled again, and the internal circuit typically consumes 9 a of current from the out pin during normal operation. low?battery detection a comparator with 15 mv hysteresis is applied to perform the low?battery detection function. when pin 9 (lbi) is at a voltage (defined by a resistor divider from the battery voltage) lower than the internal reference voltage of 0.5 v, the comparator output turns on a 50 low side switch. it pulls down the voltage at pin 10 (lbo) which has hundreds of k of pull?high resistance. if the pin 9 voltage is higher than 0.5 v+15 mv, the comparator output turns off the 50 low side switch. when this occurs, pin 10 becomes high impedance and its voltage is pulled high again. auto discharge auto discharge function is using for ensure the output voltage status after the power down occur. this function is using for communication with a digital signal. when auto discharge function is enabled, the aden is set high; the output capacitor will be discharged after the device is shutdown. the capacitors connected to the output are discharged by an integrated switch of 100 . the residual voltage on v out will be less than 0.4 v after auto discharge. applications information output voltage setting a typical application circuit is shown in figure 1, the output voltage of the converter is determined by the external feedback network comprised of r1 and r2 and the relationship is given by: v out 0.5 v 1 r1 r2 where r1 and r2 are the upper and lower feedback resistors, respectively. low battery detect level setting the low battery detect voltage of the converter is determined by the external divider network comprised of r3 and r4 and the relationship is given by: v lbi 0.5 v 1 r3 r4 where r3 and r4 are the upper and lower divider resistors respectively. inductor selection the ncp1423 is tested to produce optimum performance with a 5.6 h inductor at v in = 1.3 v, v out = 3.3 v, supplying an output current up to 200 ma. for other input / output requirements, inductance in the range 3 h to 10 h can be used according to end application specifications. selecting an inductor is a compromise between output current capability, inductor saturation limit and tolerable output voltage ripple. low inductance values can supply higher output current but also increase the ripple at output and decrease ef ficiency. on the other hand, high inductance values can improve output ripple and efficiency; however, it also limited the output current capability at the same time. another parameter of the inductor is its dc resistance. this resistance can introduce unwanted power loss and reduce overall efficiency. the basic rule is to select an inductor with lowest dc resistance within the board space limitation of the end application. capacitors selection in all switching mode boost converter applications, both the input and output terminals see impulsive voltage / current waveforms. the currents flowing into and out of the capacitors multiply with the equivalent series resistance (esr) of the capacitor to produce ripple voltage at the terminals. during the syn?rect switch?off cycle, the charges stored in the output capacitor are used to sustain the output load current. load current at this period and the esr combined and reflect as ripple at the output terminals. for all cases, the lower the capacitor esr, the lower the ripple voltage at output. as a general guideline, low esr capacitors should be used. pcb layout recommendations good pcb layout plays an important role in switching mode power conversion. careful pcb layout can help to minimize ground bounce, emi noise, and unwanted feedback that can affect the performance of the converter. hints suggested below can be used as a guideline in most situations. grounding a star?ground connection should be used to connect the output power return ground, the input power return ground, and the device power ground together at one point. all high?current paths must be as short as possible and thick enough to allow current to flow through and produce insignificant voltage drop along the path. the feedback signal path must be separated from the main current path and sense directly at the anode of the output capacitor. components placement power components (i.e. input capacitor, inductor and output capacitor) must be placed as close together as possible. all connecting traces must be short, direct and thick. high current flowing and switching paths must be kept away from the feedback (fb, pin 3) terminal to avoid unwanted injection of noise into the feedback path.
ncp1423 http://onsemi.com 12 general design procedures switching mode converter design is important. suitable choice an inductor and capacitor value can make the converter has an optimum performance. below a simple method base on the most basic first order equations to estimate the inductor and capacitor values for ncp1423 operate in continuous conduction mode (ccm) is introduced. the component value set can be used as a starting point to fine?tune the circuit operation. by all means, detail bench testing is needed to get the best performance out of the circuit. design parameters: for one cells supply application v in = 1.1 v to 1.5 v, typical 1.3 v v out = 3.3 v i out = 150 ma (200 ma max) v lb = 1.0 v v out?ripple = 30 mv p?p at i out = 150 ma calculate the feedback network: select r2 = 100 k r1 r2 v out v fb 1 r1 100 k 3.3 v 0.5 v 1 560 k calculate the low battery detect divider: v lb0 = 1.0 v select r4 = 100 k r3 r4 v lb0 v lb1 1 r3 100 k 1.0 v 0.5 v 1 100 k determine the steady state duty ratio, d for typical v in , operation will be optimized around this point: v out v in 1 1 d d 1 v in v out 1 1.3 v 3.3 v 0.606 determine the average inductor current, i lavg at maximum i out : i lavg i out 1 d 150 ma 1 0.606 381 ma assume the efficiency = 85% determine the peak inductor ripple current, i ripple?p and calculate the inductor value: assume i ripple?p is 40% of i lavg , the inductance of the power inductor can be calculated as in below: i ripple?p = 0.40 x 381 ma / = 179 ma l v in t on 2i ripple p 1.3 v 1.4 s 2 (179 ma) 5.0 h a standard value of 5.6 h is selected for initial trial. determine the output voltage ripple, v out?ripple and calculate the output capacitor value: v out?ripple = 30 mv p?p at i out = 150 ma c out i out t on v out ripple i out esr cout where t on = 1.4 s and esr cout = 0.1 , from above calculation, you need at least 14 f in order to achieve the specified ripple level at conditions stated. practically, a one level larger capacitor will be used to accommodate factors not taken into account in the calculations. therefore, a capacitor value of 22 f is selected. the ncp1423 is internal compensated for most applications. but in case additional compensation is required, the capacitor c1 can be used as external compensation adjustment to improve system dynamics.
ncp1423 http://onsemi.com 13 package dimensions s b m 0.08 (0.003) a s t dim min max min max inches millimeters a 2.90 3.10 0.114 0.122 b 2.90 3.10 0.114 0.122 c 0.95 1.10 0.037 0.043 d 0.20 0.30 0.008 0.012 g 0.50 bsc 0.020 bsc h 0.05 0.15 0.002 0.006 j 0.10 0.21 0.004 0.008 k 4.75 5.05 0.187 0.199 l 0.40 0.70 0.016 0.028 notes: 1. dimensioning and tolerancing per ansi y14.5m, 1982. 2. controlling dimension: millimeter. 3. dimension ?a? does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.15 (0.006) per side. 4. dimension ?b? does not include interlead flash or protrusion. interlead flash or protrusion shall not exceed 0.25 (0.010) per side. 5. 846b?01 obsolete. new standard 846b?02 ?b? ?a? d k g pin 1 id 8 pl 0.038 (0.0015) ?t? seating plane c h j l mm inches scale 8:1 10x 10x 8x 1.04 0.041 0.32 0.0126 5.28 0.208 4.24 0.167 3.20 0.126 0.50 0.0196 micro10 case 846b?03 issue d *for additional information on our pb?free strategy and soldering details, please download the on semiconductor soldering and mounting techniques reference manual, solderrm/d. soldering footprint* on semiconductor and are registered trademarks of semiconductor components industries, llc (scillc). scillc reserves the right to mak e changes without further notice to any products herein. scillc makes no warranty, representation or guarantee regarding the suitability of its products for an y particular purpose, nor does scillc assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including wi thout limitation special, consequential or incidental damages. ?typical? parameters which may be provided in scillc data sheets and/or specifications can and do vary in different application s and actual performance may vary over time. all operating parameters, including ?typicals? must be validated for each customer application by customer?s technical experts. scillc does not convey any license under its patent rights nor the rights of others. scillc products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the scillc product could create a sit uation where personal injury or death may occur. should buyer purchase or use scillc products for any such unintended or unauthorized application, buyer shall indemnify and hold scillc and its of ficers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, direct ly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that scillc was negligent regarding the design or manufacture of the part. scillc is an equal opportunity/affirmative action employer. this literature is subject to all applicable copyright laws and is not for resale in any manner. publication ordering information n. american technical support : 800?282?9855 toll free usa/canada europe, middle east and africa technical support: phone: 421 33 790 2910 japan customer focus center phone: 81?3?5773?3850 ncp1423/d literature fulfillment : literature distribution center for on semiconductor p.o. box 5163, denver, colorado 80217 usa phone : 303?675?2175 or 800?344?3860 toll free usa/canada fax : 303?675?2176 or 800?344?3867 toll free usa/canada email : orderlit@onsemi.com on semiconductor website : www.onsemi.com order literature : http://www.onsemi.com/orderlit for additional information, please contact your local sales representative sensefet is a trademark of semiconductor components industries, llc.

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