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njw4131 - 1 - ver.2012-08-03 switching regulator ic for boost converter w/ 40v/1.4a or 40v/1a mosfet general description package outline features output switch voltage 40v max. wide operating voltage range 4v to 35v switching current 1.4a (min.) @ a version 1.0a (min.) @ b version pwm control wide oscillation frequency 300khz to 1mhz soft-start function 4ms typ. uvlo (under voltage lockout) over current protection / thermal shutdown protection standby function package outline njw4131gm1: hsop8 njw4131r: msop8(vsp8)* *meet jedec mo-187-da product classfication part number version switching current limit (min.) package operating temperature range NJW4131GM1-A a 1.4a hsop8 -40 c to +85 c njw4131r-b b 1.0a msop8(vsp8) -40 c to +85 c the njw4131 is a boost converter with 40v/1.4a or 40v/1 a mosfet. it corresponds to high oscillating frequency, and low es r output capacitor (mlcc) within wide input range from 4.0v to 35v. therefore, the njw4131 can realize downsiz ing of an application with a few external parts. also, it has a soft start function, an over current protection and a thermal shutdown circuit. it is suitable for power supply to a car accessory, office automation equipment, industrial instrument, led and so on. njw4131r-b (msop8 (vsp8)) NJW4131GM1-A (hsop8)
njw4131 - 2 - ver.2012-08-03 pin configuration block diagram buffer pgnd v + tsd sw soft start 1.0v in- pwm er ? amp standby on/off on/off high: on low : off (standby) uvlo vref fb osc regulator rt a gnd ocp pulse by pulse 400k ? low frequency control pin function 1. sw 2. on/off 3. v + 4. rt 5. in- 6. fb 7. agnd 8. pgnd 1 4 3 2 8 5 6 7 exposed pad on backside connect to gnd 1 8 2 7 3 6 4 5 NJW4131GM1-A njw4131r-b
njw4131 - 3 - ver.2012-08-03 absolute maximum ratings (ta=25c) parameter symbol maximum ratings unit supply voltage v + +40 v sw pin voltage v sw +40 v in- pin voltage v in- -0.3 to +6 v on/off pin voltage v on/off +40 v power dissipation p d hsop8 790 (*1) 2,500 (*2) msop8(vsp8) 595 (*1) 805 (*2) mw junction temperature range t j -40 to +150 c operating temperature range t opr -40 to +85 c storage temperature range t stg -40 to +150 c (*1): mounted on glass epoxy board. (76.21 14.31.6mm:eia/jdec standard size, 2layers) (*2): mounted on glass epoxy board. (76.2114. 31.6mm:eia/jdec standard size, 4layers), internal foil area: 74.274.2mm recommended operating conditions parameter symbol min. typ. max. unit supply voltage v + 4.0 ? 35 v timing resistance r t 18 27 68 k ? oscillating frequency fosc 300 700 1,000 khz
njw4131 - 4 - ver.2012-08-03 electrical characteristics (unless other noted, v + =v on/off =12v, r t =27k ? , ta=25 c) parameter symbol test condition min. typ. max. unit under voltage lockout block on threshold voltage v t_on v + = l h 3.8 3.9 4.0 v off threshold voltage v t_off v + = h l 3.7 3.8 3.9 v hysteresis voltage v hys 60 100 ? mv soft start block soft start time t ss v b =0.95v 2 4 8 ms oscillator block oscillation frequency f osc 630 700 770 khz oscillation frequency (low frequency control) f osc_low v in- =0.4v, v fb =0.65v ? 270 ? khz rt pin voltage v rt 0.240 0.275 0.310 v oscillate supply voltage fluctuations f dv v + =4v to 35v ? 1 ? % oscillate temperature fluctuations f dt ta = - 4 0 c to +85 c ? 3 ? % error amplifier block reference voltage v b -1.0% 1.00 +1.0% v input bias current i b -0.1 ? +0.1 a open loop gain a v ? 80 ? db gain bandwidth g b ? 0.6 ? mhz output source current i om+ v fb =1v, v in- =0.9v 8 16 24 a output sink current i om- v fb =1v, v in- =1.1v 1 2 4 ma pwm comparate block maximum duty cycle m ax d uty v in- =0.9v 85 90 95 % output block a version, i sw =1a ? 0.2 0.4 ? output on resistance r on b version, i sw =1a ? 0.2 0.4 ? a version 1.4 1.7 2.0 a switching current limit i lim b version 1 1.35 1.7 a switching leak current i leak v on/off =0v, v sw =40v ? ? 1 a on/off block on control voltage v on v on/off = l h 1.6 ? v + v off control voltage v off v on/off = h l 0 ? 0.5 v pull-down resistance r pd ? 400 ? k ? general characteristics quiescent current i dd r l =no load, v in- =0.9v, v fb =0.65v ? 2.3 2.8 ma standby current i dd_stb v on/off =0v ? ? 1 a
njw4131 - 5 - ver.2012-08-03 typical applications c nf r nf pgnd 8 7 6 5 1 2 3 4 fb a gnd in- rt v + c fb r2 c out l sbd njw4131 v in c in1 r1 v out r fb r t sw on/off on/off high: on low: off (standby) c in2
njw4131 - 6 - ver.2012-08-03 characteristics 100 1000 10 100 oscillation frequency f osc (khz) timing resistor vs.oscillation frequency (v + =12v, ta=25 o c) timing resistor r t (k ? ) 80 85 90 95 100 100 1000 maximum duty cycle m ax d uty (%) maximum duty cycle vs. oscillator frequency (v + =12v, v in- =0.9v, ta=25 o c) oscillator frequency f osc (khz) 690 695 700 705 710 0 10203040 oscillation frequency f osc (khz) supply voltage v + (v) oscillation frequency vs. supply voltage (r t =27k ? , ta=25 o c) 0.99 0.995 1 1.005 1.01 0 10203040 reference voltage v b (v) supply voltage v + (v) reference voltage vs. supply voltage (ta=25 o c) 0 1 2 3 4 010203040 quiescent current i dd (ma) supply voltage v + (v) quiescent current vs. supply voltage (r t =27k ? , r l =no load, v in- =0.9v, v fb =0.65v, ta=25 o c) 0 15 30 45 60 0 45 90 135 180 0.1 1 10 100 1000 10000 error amplifier block voltage gain, phase vs. frequency (v + =12v, gain=40db, ta=25 o c) phase (deg) frequency f (khz) voltage gain av (db) phase gain
njw4131 - 7 - ver.2012-08-03 characteristics 660 680 700 720 740 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) oscillator frequency f osc (khz) oscillator frequency vs. temperature (v + =12v, r t =27k ? ) 0.99 0.995 1 1.005 1.01 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) reference voltage v b (v) reference voltage vs. temperature (v + =12v) 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) limited switching current i lim (a) limited switching current vs. temperature (a ver.) v + =12v v + =35v v + =4.0v 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) limited switching current i lim (a) limited switching current vs. temperature (b ver.) v + =12v v + =35v v + =4.0v 0 0.1 0.2 0.3 0.4 0.5 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) output on resistance r on ( ? ) output on resistance vs.temperature (a ver., i sw =1a) v + =4.0v,12v,40v 0 0.1 0.2 0.3 0.4 0.5 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) output on resistance r on ( ? ) output on resistance vs.temperature (b ver., i sw =1a) v + =4.0v,12v,40v
njw4131 - 8 - ver.2012-08-03 characteristics 3.7 3.75 3.8 3.85 3.9 3.95 4 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) threshold voltage (v) under voltage lockout voltage vs. temperature v t_off v t_on 2 3 4 5 6 7 8 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) soft start time tss (ms) soft start time vs. temperature (v + =12v, v b =0.95v) 84 86 88 90 92 94 96 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) maximum duty cycle m ax d uty (%) maximum duty cycle vs. temperature (v + =12v, r t =27k ? . v in- =0.9v) 0 0.5 1 1.5 2 2.5 3 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) switching leak current i leak ( a) switching leak current vs. temperature (v + =12v,v on/off =0v, v sw =40v) 0 0.5 1 1.5 2 2.5 3 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) quiescent current i dd (ma) quiescent current vs. temperature (r t =27k ? , r l =no load, v in- =0.9v, v fb =0.65v) v + =4.0v v + =12v v + =35v 0 0.2 0.4 0.6 0.8 1 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) standby current i dd_stb ( a) standby current vs. temperature (v on/off =0v) v + =35v v + =12v v + =4.0v
njw4131 - 9 - ver.2012-08-03 pin discription pin number pin name function 1 sw switch output pin of power mosfet 2 on/off on/off control pin the on/off pin internally pulls down with 400k ? . normal operation at the time of high level. standby mode at t he time of low level or open. 3 v + power supply pin for ic control 4 rt oscillating frequency setting pin by timing resistor. oscillating frequency should set between 300khz and 1mhz. 5 in- output voltage detecting pin connects output voltage through the resistor divider tap to this pin in order to voltage of the in- pin become 1.0v. 6 fb feedback setting pin the feedback resistor and capacitor are connected between the fb pin and the in- pin. 7 agnd analog gnd pin 8 pgnd power gnd pin ? exposed pad connect to gnd (only hsop8 pkg) description of block features 1. basic functions / features error amplifier section (er ? amp) 1.0v1% precise reference voltage is connecte d to the non-inverted input of this section. to set the output voltage, connects converter's output to inve rted input of this section (in- pin). if requires output voltage, inserts resistor divider. this amp section has high gain and ex ternal feedback pin (fb pin). it is easy to insert a feedback resistor and a capacitor between the fb pin and the in- pin, making possi ble to set optimum loop compensation for each type of application. oscillation circuit section (osc) oscillation frequency can be set by inserting resistor between the rt pin and gnd. referring to the sample characteristics in "timing resistor and oscillation frequency", set oscillation between 300khz and 1mhz. njw 4131 application manual technical information
njw4131 - 10 - ver.2012-08-03 description of block features (continued) pwm comparator section (pwm) this section controls th e switching duty ratio. pwm comparator receives the signal of the error amplif ier and the triangular wave, and controls the duty ratio between 0% and 90% (typ.). the timing chart is shown in fig.1. sw pin fb pin voltage on off osc wavef orm (ic internal) max imu m dut y : 90% max duty setting fig. 1. timing chart pwm comparator and sw pin power mosfet (sw output section) the power is stored in the inductor by the switch operation of built-in power mosfet. the output current is limited to 1.4a(min.) @a version and 1.0a(min.) @b version by the overcurrent protection function. power supply, gnd pin (v + and pgnd, agnd) in line with switching element drive, current flows in to the ic according to frequency. if the power supply impedance provided to the power supply ci rcuit is high, it will not be possible to take advantage of ic performance due to input voltage fluctuation. therefore insert a bypass capacitor close to the v + pin ? the agnd pin connection in order to lower high frequency impedance. njw 4131 application manual technical information
njw4131 - 11 - ver.2012-08-03 description of block features (continued) 2. additional and protection functions / features under voltage lockout (uvlo) the uvlo circuit operating is released above v + =3.9v(typ.) and ic operation starts. when power supply voltage is low, ic does not operate because the uvlo circuit operates . there is 100mv width hysteresis voltage at rise and decay of power supply voltage. hysteresis prevents the malfunction at the time of uvlo operating and releasing. soft start function (soft start) the output voltage of the converter gradually rises to a set value by the soft start function. the soft start time is 4ms (typ). it is defined with the time of the error amplifie r reference voltage becoming from 0v to 0.95v. the soft start circuit operates after the release uvlo and/or recove ry from thermal shutdown. the operating frequency is controlled with a low frequency, approximately 40% of the set value by the timing resistor, until voltage of the in- pin becomes approximately 0.4v. sw pin 1.0v fb pin voltage on off vref, in- pin voltage osc wavef orm max duty setting steady operaton soft start effective period to v b =1.0v soft start time: tss=4ms(typ.) to v b =0.95v uvlo(3.9v typ.) release, standby, recover from thermal shutdow n low frequency control v in- =approx 0.4v fig. 2. startup timing chart njw 4131 application manual technical information
njw4131 - 12 - ver.2012-08-03 description of block features (continued) over current protection circuit (ocp) at when the switching current becomes i lim or more, the overcurrent protection circuit is stopped the mosfet output. the switching output holds low level down to next pulse output at ocp operating. the njw4131 output returns automatically along with re lease from the over current condition because the ocp is pulse-by-pulse type. fig.3. shows the timing chart of th e over current protection detection. if voltage of the in- pin becomes less than 0.4v, the oscillation frequency decreases to approximately 40% and the energy consumption is suppressed. sw pin on off osc wavef orm sw itching current i lim 0 fb pin voltage max duty setting static status detec t overcurrent static status fig3. timing chart at over current detection if temperature increases, switching current limit (i lim ) decreases due to thermal characteristics (see characteristics "limited switching current vs. temperat ure"). you should consider applicat ion temperature and set a peak current less than switching current limit. thermal shutdown function (tsd) when junction temperature of the njw4131 exceeds the 170c*, internal thermal shutdown circuit function stops sw function. when junction temperature decreases to 150c* or less, sw operation returns with soft start operation. the purpose of this function is to prev ent malfunctioning of ic at the high junc tion temperature. therefore it is not something that urges positive use. you should make sure to operate within the junction temperature range rated (150 c). (* design value) on/off function (standby control) the njw4131 stops the operating and becomes standby stat us when the on/off pin becomes less than 0.5v. the on/off pin internally pulls down with 400k ? , therefore the njw4131 becomes standby mode when the on/off pin is open. you should connect this pin to v + when you do not use on/off function. njw 4131 application manual technical information
njw4131 - 13 - ver.2012-08-03 application information inductors large currents flow into inductor, therefore you must provide current capacity that does not saturate. reducing l, the size of the inductor can be smaller. however, peak current increases and adversely affecting efficiency. on the other hand, increasing l, peak current can be reduced at switching time. therefore conversion efficiency improves, and output ripple voltage reduces. above a certain level, increasing inductance windings increases loss (copper loss) due to the resistor element. ideally, the value of l is set so that inductance current is in continuous conduction mode. however, as the load curr ent decreases, the current waveform changes from (1) ccm: continuous conduction mode (2) critical mode (3) dcm: discontinuous conduction mode (fig. 4.). in discontinuous mode, peak current increases with respec t to output current, and conversion efficiency tend to decrease. depending on the situation, increase l to widen the load current area to maintain continuous mode. catch diode when the switch element is in off cycle, power stored in the inductor flows via the catch diode to the output capacitor. therefore during each cycle current flows to the diode in response to load current. because diode's forward saturation voltage and current accumulation caus e power loss, a schottky barrier diode (sbd), which has a low forward saturation voltage, is ideal. an sbd also has a short reverse recove ry time. if the reverse recovery time is long, through current flows when the switching transistor transitions from off cycle to on cycle. this current may lower efficiency and affect such factors as noise generation. when the switch element is in on cycle, a reverse volta ge flows to sbd. therefore you should select a sbd that has reverse voltage rating greater than maximum output vo ltage. the power loss, which stored in output capacitor, will be increase due to increasing reverse current through sbd at high temperature. therefore, there is cases preferring reverse current characteristics to forward cu rrent characteristic in order to improve efficiency. input capacitor transient current flows into the input section of a swit ching regulator responsive to frequency. if the power supply impedance provided to the power supply circuit is large, it will not be possible to take advantage of njw4131 performance due to input voltage fluctuation. therefore in sert an input capacitor as close to the mosfet as possible. output capacitor an output capacitor stores power from the induc tor, and stabilizes voltage provided to the output. when selecting an output capacitor, you must consider equi valent series resistance (esr ) characteristics, ripple current, and breakdown voltage. also, the ambient temperature affects capacitors, decreasing capacitance and increasing esr (at low temperature), and decreasing lifetime (at high temperature) . concerning capacitor rating, it is advisable to allow sufficient margin. output capacitor esr characteristics have a major influe nce on output ripple noise. a capacitor with low esr can further reduce ripple voltage. be sure to note the follo wing points; when ceramic capacit or is used, the capacitance value decreases with dc voltage applied to the capacitor. 0 inductor current ? i l t off t on peak current ipk frequency f osc current (1) continuous conduction mode (2) critical mode (3) continuous conduction mode njw 4131 application manual technical information fig. 4. inductor current state transition
njw4131 - 14 - ver.2012-08-03 application information (continued) board layout in the switching regulator application, because the cu rrent flow corresponds to the oscillation frequency, the substrate (pcb) layout becomes an important. you should attempt the transition voltage decrease by maki ng a current loop area minimize as much as possible. therefore, you should make a current flowing line thick and short as much as possible. fig.5. shows a current loop at boost converter. c out l sbd c in v in c out l sbd c in v in njw4131 built-in sw njw4131 built-in sw (a) boost converter sw on (b) boost converter sw off fig. 5. current loop at boost converter concerning the gnd line, it is preferred to separate the power system and the signal system, and use single ground point. the voltage sensing feedback li ne should be as far away as possible from the inductance. because this line has high impedance, it is laid out to avoid the influence noise caused by flux leaked from the inductance. fig. 6. shows example of wiring at boost conv erter. fig. 7 shows the pcb layout example. sw agnd in- rt v + c fb r2 c out l sbd njw4131 c in r1 v out r fb r t v in pgnd to avoid the influence of the voltage drop, the output voltage should be detected near the load. r l because in- pin is high impedance, the voltage detection resistance: r1/r2 is put as much as possible near ic(in-). separate digital(signal) gnd f rom pow er gnd (bypass capacitor) fig. 6. board layout at boost converter njw 4131 application manual technical information
njw4131 - 15 - ver.2012-08-03 application information (continued) c in1 c out c fb r fb r1 r2 c nf r nf v out power gnd area feed back signal gnd out gnd in v in signal gnd area r t c in2 on/off sbd l connect signal gnd line and power gnd line on backside pattern fig. 7 layout example (upper view) technical information njw 4131 application manual
njw4131 - 16 - ver.2012-08-03 calculation of package power a lot of the power consumption of boost converter occurs from the internal switchin g element (power mosfet). power consumption of njw4131 is roughly estimated as follows. input power: p in = v in i in [w] output power: p out = v out i out [w] diode loss: p diode = v f i l(avg) off duty [w] njw4131 power consumption: p loss = p in ? p out ? p diode [w] where: v in : input voltage for converter i in : input current for converter v out : output voltage of converter i out : output current of converter v f : diode's forward saturation voltage i l(avg) : inductor average current off duty : switch off duty efficiency ( ) is calculated as follows. = (p out p in ) 100 [%] you should consider temperature derating to the calculated power consumption: p d . you should design power consumption in rated range refe rring to the power dissipation vs. ambient temperature characteristics (fig. 8). 0 500 1000 1500 2000 2500 3000 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) power dissipation p d (mw) njw4131gm1 (hsop8 package) power dissipation vs. ambient temperature (tj= ~150 o c) at on 4 layer pc board at on 2 layer pc board 0 200 400 600 800 1000 -50 -25 0 25 50 75 100 125 150 ambient temperature ta ( o c) power dissipation p d (mw) njw4131r (msop8(vsp8) package) power dissipation vs. ambient temperature (tj= ~150 o c) at on 4 layer pc board at on 2 layer pc board mounted on glass epoxy board. (76.2 114.3 1.6mm:eia/jdec standard size, 2layers) mounted on glass epoxy board. (76.2 114.3 1.6mm:eia/jdec standard size, 4layers), internal cu area: 74.2 74.2mm fig.8. power dissipation vs. ambi ent temperature characteristics technical information njw 4131 application manual
njw4131 - 17 - ver.2012-08-03 application design examples step-up application circuit ic input voltage : NJW4131GM1-A : v in =12v output voltage : v out =24v output current : i out =0.3a oscillation frequency : fosc=700khz c nf 6,800pf r nf 8.2k ? pgnd 8 7 6 5 1 2 3 4 fb a gnd in- rt v + c fb 120pf r2 300k ? c out 10 f/50v l 47 h/1.52a sbd njw4131 v in =12v c in1 10 f/50v r1 13k ? v out =24v r fb 27k ? r t 27k ? sw on/off on/off high: on low: off (standby) c in2 0.1 f/50v reference qty. part number description manufacturer ic 1 NJW4131GM1-A internal 40v mosfet sw.reg. ic new jrc l 1 cdrh8d38np-470n inductor 47 h, 1.52a sumida d 1 cms11 schottky diode 40v, 2a toshiba c in1 , c out 2 umk325bj106mm ceramic capacitor 3225 10 f, 50v, x5r taiyo yuden c in2 1 0.1 f ceramic capacitor 1608 0.1 f, 5 0 v, b std. c nf 1 6,800pf ceramic capacitor 1608 6,800pf, 50v, b std. c fb 1 120pf ceramic capacitor 1608 120pf, 50v, ch std. r1 1 13k ? resistor 1608 13k ? , 1%, 0.1w std. r2 1 300k ? resistor 1608 300k ? , 1%, 0.1w std. r t 1 27k ? resistor 1608 27k ? , 1%, 0.1w std. r nf 1 8.2k ? resistor 1608 8.2k ? , 5%, 0.1w std. r fb 1 27k ? resistor 1608 27k ? , 5%, 0.1w std. technical information njw 4131 application manual
njw4131 - 18 - ver.2012-08-03 application design examples (continued) setting oscillation frequency from the oscillation frequency vs. timing resistor characteristic, r t =27 [k ? ], t=1.43[ s] at fosc=700khz. step-up converter duty ratio is shown with the following equation. [] % v v duty out in 50 100 24 12 1 100 1 = ? ? ? ? ? ? ? = ? ? ? ? ? ? ? ? ? = therefore, t on =0.72 [ s], t off =0.71 [ s] fig. 9. inductor current waveform selecting inductance the inductor's average current equals input current (i in ). estimated efficiency ( ) is 90% and calculates input current. [] a . . . v i v i in out out in 67 0 12 9 0 3 0 24 = = = to assume maximum output current: 0.3a, and the inducto r ripple current should be set not to exceed the minimum switching limiting current: i lim =1.4a (min.). ? i l is inductance ripple current. when to ? i l = input current 30%: ? i l = 0.3 i in = 0.3 0.67 = 0.2 [a] this obtains inductance l. on l in t i v l ? = ] h [ . . . ? = = 47 2 43 72 0 2 0 12 inductance l is a theoretical value. the optimum value vari es according such factors as application specifications and components. fine-tuning should be done on the actual device. this obtains the peak current ipk at switching time. ] a [ . . . i i ipk l in 77 0 2 2 0 67 0 2 = + = ? + = the current that flows into the inductance provides sufficient margin for peak current at switching time. in the application circuit, use l=47 h, 1.52a. 0 t off t on period: t frequency: f osc =1/t inductance current: ? i l output current: i out peak current: ipk technical information njw 4131 application manual
njw4131 - 19 - ver.2012-08-03 application design examples (continued) selecting the output capacitor the output capacitor is an important component that determi nes output ripple noise. equivalent series resistance (esr), ripple current, and capacitor breakdown voltage ar e important in determining the output capacitor. the output ripple noise can be expr essed by the following formula. l p p ripple i v esr ? = ? ) ( when selecting output capacitance, select a capaci tor that allows for sufficient ripple current. the effective ripple current that flows in a capacitor (i rms ) is obtained by the following equation. ] arms [ . . . i i i out pk rms 71 0 3 0 77 0 2 2 2 2 = ? = ? = consider sufficient margin, and use a ca pacitor that fulfil ls the above spec. in the application circuit, use c out =10 f/50v. setting output voltage the output voltage v out is determined by the relative resistances of r1, r2. the curr ent that flows in r1, r2 must be a value that can ignore the bias current that flows in er amp. ] v [ . k k v r r v b out 07 24 1 1 13 300 1 1 2 = ? ? ? ? ? ? + = ? ? ? ? ? ? + = it is easy to make a feedback loop, because the error amplifier output connects to fb pin. dc gain affects voltage sensing of the error amplifier. if ac gain increases, it affects stability of regulator due to ac gain which contains switching noise, ripple noise and the others. recommended way of feedback, is high dc gain and low ac gain. in this application, a feedback resistor r nf =8.2k ? and capacitor c nf =6,800pf are connected in serial. however, if the ac gain is lowered too much, it happens slower transient response against fast load changes. the optimum value varies according such factors as applic ation specifications and co mponents. fine-tuning should be done on the actual device. technical information njw 4131 application manual
njw4131 - 20 - ver.2012-08-03 application characteristics :NJW4131GM1-A efficiency vs. outputcurrent (v out =24v) 0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 output current i out [ma] efficiency [%] f=700khz l=47 h v in =9v v in =12v v in =18v load regulation 23.0 23.2 23.4 23.6 23.8 24.0 24.2 24.4 24.6 24.8 25.0 1 10 100 1000 output current i out [ma] output voltage v out [v] f=700khz l=47 h v in =9v v in =12v v in =18v [caution] the specifications on this databook are only given for information , without any guarantee as regards either mistakes or omissions. the application circuits in this databook are described only to show representative usages of the product and not intended for the guarantee or permission of any right including the industrial rights. njw 4131 application manual technical information

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