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switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) pin configuration (top view) description m51996a is the primary switching regulator controller which is especially designed to get the regulated dc voltage from ac power supply. this ic can directly drive the mos-fet with fast rise and fast fall output pulse and with a large-drive totempole output. type m51996a has the functions of not only high frequency osc and fast output drive but also current limit with fast response and high sensibility so the true "fast switching regulator" can be realized. the m51996a is equivalent to the m51978 with externally re- settable ovp(over voltage protection)circuit. features 500khz operation to mos fet output current...............................................................?a output rise time 60ns,fall time 40ns modified totempole output method with small through current compact and light-weight power supply ?mall start-up current............................................100? typ. ?ig difference between "start-up voltage" and "stop voltage" makes the smoothing capacitor of the power input section small. start-up threshold 16v,stop voltage 10v ?ackages with high power dissipation are used to with-stand the heat generated by the gate-drive current of mos fet. 14-pin dip,16-pin sop 1.5w(at 25?) simplified peripheral circuit with protection circuit and built-in large-capacity totempole output ?igh-speed current limiting circuit using pulse-by-pulse method(clm+pin) ?ver-voltage protection circuit with an externally re-settable latch(ovp) ?rotection circuit for output miss action at low supply voltage(uvlo) high-performance and highly functional power supply ?riangular wave oscillator for easy dead time setting ?oft start function by expanding period application feed forward regulator,fly-back regulator 1 14 11 12 13 1 4 3 2 10 5 9 6 8 7 16 13 14 15 1 4 3 2 12 5 11 6 10 7 9 8 recommended operating conditions supply voltage range............................................12 to 30v operating frequency.................................less than 500khz oscillator frequency setting resistance ?-on pin resistance r on ...........................10k to 75k w ?-off pin resistance r off ..........................2k to 30k w collector v out emitter ovp det f/b
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) block diagram f/b collector emitter v v a 31 31 ? ?.15 -6 v reg +0.2 symbol ratings unit parameter conditions absolute maximum ratings v cc supply voltage collector voltage output current v reg terminal output current soft terminal voltage v c i o i vreg ma mw/?c -0.3 to +3 8 6 -10 -1 -2 clm+ terminal voltage ovp terminal current det terminal voltage power dissipation thermal derating operating temperature storage temperature p d k t opr t stg w 1.5 12 -30 to +85 -40 to +125 ta=25?c ta>25?c peak continuous 2 v soft v clm+ i ovp v det i fb i ton i toff f/b terminal current t-on terminal input current t-off terminal input current ?c ?c ma ma v ma v v ma note 1."+" sign shows the direction of current flowing into the ic and "-" sign shows the current flowing out from the ic. 2.the low impedance voltage supply should not be applied to the ovp terminal. reg(7.8v) det gnd voltage regulator v out 2.5v op amp pwm comparator current limit detection oscillator (triangle) clm+ latch 500 6s 1s 3k 1s 1s 15.2k 7.1v 5.8v ovp cf t-on t-off v cc soft under voltage lock out pwm latch
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) d vcc=vcc (start) - vcc (stop) operation stop voltage stand-by current operating supply voltage range operating circuit current current at 0% duty limits min. typ. max. symbol test conditions unit parameter electrical characteristics (v cc =18v, ta=25?, unless otherwise noted) v vcc(stop) 30 block v cc(start) v cc i fbmind 16.2 17.2 v 9.0 9.9 10.9 6.3 7.6 100 v w v db ? ? v f/b terminal voltage ovp terminal resistance difference supply voltage between operation stop and ovp reset detection voltage det terminal input current voltage gain of detection amp ovp terminal hysteresis voltage ovp reset supply voltage d i fb v fb r fb v cc(stop) - v ccovpc v det i indet g avdet v thovph d v thovp i thovp i inovp v ccovpc
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 4 typical characteristics 0 300 600 900 1200 1500 1800 0 25 50 75 100 125 150 85 thermal derating (maximum rating) ambient temperature ta(?)
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 5 clm+ terminal current vs. clm+ terminal voltage 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -100 -200 -300 -400 0 clm+ terminal voltage v clm +(v)
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 6 voltage gain of detection amp vs. frequency 50 40 30 20 10 0 frequency f(hz)
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 7 ambient temperature ta(?) oscillator frequency vs. ambient temperature -60 -40 -20 0 20 40 60 80 100 r on =24k w r off =20k w c f =330pf
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 8 ovp terminal input voltage vs. input current 1 10 100 1m 0.2 0.4 0.6 0.8 1.0 ovp terminal input voltage v ovp (v)
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) function description 9 type m51996ap and m51996afp are especially designed for off-line primary pwm control ic of switching mode power supply to get dc voltage from ac power supply. using this ic,smart smps can be realized with reasonable cost and compact size as the number of external electric parts can be reduced and also parts can be replaced by reasonable one. in the following circuit diagram,mos-fit is used for output transistor,however bipolar transistor can be replaced with no problem. m51996ap/fp dc output fig.1 application example for feed forward regulator ovp ac input
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 10 start-up circuit section the start-up current is such low current level as typical 100 a,as shown in fig.3,when the vcc voltage is increased from low level to start-up voltage vcc (start) . in this voltage range,only a few parts in this ic,which has the function to make the output voltage low level,is alive and icc current is used to keep output low level.the large voltage difference between vcc (start) and vcc (stop) makes start-up easy,because it takes rather long duration from vcc (start) to vcc (stop) . oscillator section the oscillation waveform is the triangle one.the on-duration of output pulse depends on the rising duration of the triangle waveform and dead-time is decided by the falling duration. the rising duration is determined by the product of external resistor r on and capacitor c f and the falling duration is mainly determined by the product of resistor r off and capacitor c f . (1)oscillator operation when soft circuit does not operate fig.4 shows the equivalent charging and discharging circuit diagram of oscillator. the current flows through r on from the constant voltage source of 5.8v.c f is charged up by the same amplitude as r on current,when internal switch sw1,sw2 is switched to "charging side".the rise rate of c f terminal is given as vcc (stop) vcc (start) icco 11ma icc l 100?
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 11 (2)oscillator operation when the soft(soft start) circuit is operating. output transistor is protected from rush current by clm function at the start time of power on.soft terminal is used to improve the rising response of the output voltage of power supply(prevention of overshooting). the on duration of output is kept constant,and the off duration is extended as the soft terminal voltage becomes lower by the soft start circuit of this ic. the maximum value of extension is set internally at approximately sixteen times of the maximum on duartion. the features of this method are as follows: 1 it is ideal for primary control as ic driving current is supplied from the third widing of the main transformer at the start-up because constant on duration is obtained from start-up. 2 it is possible to get a wide dynamic range for on/off ratio by pulse-by-pulse current limit circuit. 3 the response characteristics at power-on is not affected by input voltage as the pulse-by-pulse limit current value is not affected by the input voltage. fig.6 shows the circuit diagram of the soft start.if soft terminal voltage is low,t-off terminal voltage bocomes low and v t-off in equations (3) and (4) become low. fig.7 oscillator waveform when the soft circuit is operating
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 12 fig.9 pwm comparator pwm latch and current limit latch section + - f/b cf from osc to output point c point b latch current pwm comp point a 5.8v
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 13 fig.13 voltage detector circuit section(det) fig.14 schmatic diagram of voltage detector circuit section(det) - + op amp 2.5v det f/b 500 w 3k 6s 1s 7.1v 7.1v det f/b 3k 500 w 1s 6s 10s 1.2k 10.8k 10.8k 5.4k it is necessary to input the sufficient larger current(800? to 8ma)than i2 for triggering the ovp operation. the reason to decrease i2 is that it is necessary that icc at the ovp rest supply voltage is small. it is necessary that ovp state holds by circuit current from r1 in the application example,so this ic has the characteristic of small icc at the ovp reset supply voltage(~stand-by current + 20?) on the other hand,the circuit current is large in the higher supply voltage,so the supply voltage of this ic doesn't become so high by the voltage drop across r1. this characteristic is shown in fig.16. the ovp terminal input current in the voltage lower than the ovp threshold voltage is based on i2 and the input current in the voltage higher than the ovp threshold voltage is the sum of the current flowing to the base of q3 and the current flowing from the collector of q2 to the base. for holding in the latch state,it is necessary that the ovp terminal voltage is kept in the voltage higher than v be of q3. so if the capacitor is connected between the ovp terminal and gnd,even though q2 turns on in a moment by the surge voltage,etc,this latch action does not hold if the ovp terminal voltage does not become higher than v be of q3 by charging this capacitor. for resetting ovp state,it is necessary to make the ovp terminal voltage lower than the ovp l threshold voltage or make vcc lower than the ovp reset supply voltage. as the ovp reset voltage is settled on the rather high voltage of 9.0v,smps can be reset in rather short time from the switch-off of the ac power source if the smoothing capacitor is not so large value. ovp circuit(over voltage protection circuit)section fig.15 detail diagram of ovp circuit i 1 100? 7.8v 8k 12k 400 2.5k i 2 q3 q1 q2 vcc ovp gnd i1=0 when ovp operates but it becomes high impedance state when lower than 2.5v det terminal and f/b terminal have inverting phase characteristics each other,so it is recommended to connect the resistor and capacitor in series between them for phase compensation.it is very important one can not connect by resistor directly as there is the voltage difference between them and the capacitor has the dc stopper function. ovp circuit is basically positive feedback circuit constructed by q2,q3 as shown in fig.15. q2,q3 turn on and the circuit operation of ic stops,when the input signal is applied to ovp terminal.(threshold voltage ~ 750mv) the current value of i2 is about 150? when the ovp does not operates but it decreases to about 2? when ovp operates.
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 14 just after the start-up,the icc current is supplied from cvcc,however,under the steady state condition ,ic will be supplied from the third winding or bias winding of transformer,the winding ratio of the third winding must be designed so that the induced voltage may be higher than the operation-stop voltage vcc (stop) . the vcc voltage is recommended to be 12v to 17v as the normal and optimum gate voltage is 10 to 15v and the output voltage(v oh ) of type m51996ap/fp is about(vcc-2v). it is not necessary that the induced voltage is settled higher than the operation start-up voltage vcc (start) ,and the high gate drive voltage causes high gate dissipation,on the other hand,too low gate drive voltage does not make the mos-fet fully on- state or the saturation state. supply voltage vcc(v) 0 10 20 30 40 0
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 15 current characteristics of type m51996ap/fp. the input voltage(v in(stop) ),at which the ic operation stops,is decided by the ratio of third winding of transformer. the v in(start) and v in(stop) are given by following equations. m51996a gnd vcc fig.19 how to design the conductor-pattern of type m51996a on pc board(schematic example) collector emitter cvcc it is required that the v in(start) must be higher than v in(stop) . when the third winding is the "fly back winding" or "reverse polarity",the v in(start) can be fixed,however,v in(stop) can not be settled by this system,so the auxiliary circuit is required. to avoid the abnormal ic operation,it is recommended to design the vcc is not vary abruptly and has few spike voltage,which is induced from the stray capacity between the winding of main transformer. to reduce the spike voltage,the cvcc,which is connected between vcc and ground,must have the good high frequency characteristics. to design the conductor-pattern on pc board,following cautions must be considered as shown in fig.19. (a)to separate the emitter line of type m51996a from the gnd line of the ic (b)the locate the c vcc as near as possible to type m51996a and connect directly (c)to separate the collector line of type m51996a from the vcc line of the ic (d)to connect the ground terminals of peripheral parts of ics to gnd of type m51996a as short as possible (3)notice to the vcc,vcc line and gnd line v in(start) r1 ?i ccl + ( + 1) ?vcc (start) r2 r1 ~ ...............(7) v in(stop) (vcc (stop)- v f) ? ............(8) ~ n b n p + 2 1 v' in rip(p-p) where i ccl is the operation start-up current of ic vcc (start) is the operation start-up voltage of ic vcc (stop) is the operation stop voltage of ic v f is the forward voltage of rectifier diode v' in(p-p) is the peak to peak ripple voltage of vcc terminal ~ n p n b v' in rip(p-p) output r clm main transformer third winding (4)power supply circuit for easy start-up when ic start to operate,the voltage of the c vcc begins to decrease till the c vcc becomes to be charged from the third winding of main-transformer as the icc of the ic increases abruptly.in case shown in fig.17 and 18,some "unstable start- up" or "fall to start-up" may happen, as the charging interval of c vcc is very short duration;that is the charging does occur only the duration while the induced winding voltage is higher than the c vcc voltage,if the induced winding voltage is nearly equal to the "operation-stop voltage" of type m51996a. it is recommended to use the 10 to 47? for c vcc1 ,and about 5 times capacity bigger than c vcc1 for c vcc2 . m51996a cvcc1 main transformer third winding cvcc2 gnd vcc r1 fig.20 dc source circuit for stable start-up
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 16 it is recommended to connect the capacitor between ovp terminal and gnd for avoiding the miss operation by the spike noise. the ovp terminal is connected with the sink current source (~150?) in ic when ovp does not operate,for absorbing the leak current of the photo coupler in the application. so the resistance between the ovp terminal and gnd for leak- cut is not necessary. if the resistance is connected,the supply current at the ovp reset supply voltage becomes large. as the result,the ovp reset supply voltage may become higher than the operation stop voltage. in that case,the ovp action is reset when the ovp is triggered at the supply voltage a little high than the operation stop voltage. so it should be avoided absolutely to connect the resistance between the ovp terminal and gnd. (1)to avoid the miss operation of ovp ovp circuit m51996a ovp gnd vcc fig.21 peripheral circuit of ovp terminal 5.6k photo coupler m51996a main transformer third winding cvcc gnd vcc fig.23 ovp setting method using the induced third winding voltage on fly back system the reset time may becomes problem when the discharge time constant of c fin ?(r1+r2) is long. under such the circuit condition,it is recommended to discharge the c vcc forcedly and to make the vcc low value;this makes the ovp-reset time fast. (2)application circuit to make the ovp-reset time fast for the over voltage protection (ovp),the induced fly back type third winding voltage can be utilized,as the induced third winding voltage depends on the output voltage.fig.23 shows one of the example circuit diagram. (3)ovp setting method using the induced third winding voltage on fly back system m51996a fig.22 example circuit diagram to make the ovp-reset-time fast ~ r1 r2 gnd vcc to main transformer c fin cvcc the time constant of this part should be short 470 w ovp to reg or vcc (4)method to control for on/off using the ovp terminal you can reset ovp to lower the ovp terminal voltage lower than v thovpl . so you can control for on/off using this nature. the application is shown in fig.24. the circuit turns off by sw off and turns on by sw on in this application. of course you can make use of the transistor or photo-transistor instead of sw. fig.24 method to control for on/off using the ovp terminal sw on/off m51996a reg 5.1k
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 17 fig.25 shows the example circuit diagrams around the clm+ terminal.it is required to connect the low pass filter,in order to reduce the spike current component,as the main current or drain current contains the spike current especially during the turn-on duration of mos-fit. 1,000pf to 22,000pf is recommended for c nf and the r nf1 and r nf2 have the functions both to adjust the "current- detecting-sensitivity" and to consist the low pass filter. (1)peripheral circuit of clm+ terminal current limiting circuit m51996a gnd vcc fig.25 peripheral circuit diagram of clm+ terminal r1 cvcc input smoothing capacitor c fin collector clm+ v out emitter c nf r nf1 r nf2 r clm to design the r nf1 and r nf2 ,it is required to consider the influence of clm+ terminal source current(i inclm +), which value is in the range of 90 to 270?. in order to be not influenced from these resistor paralleled value of r nf1 and r nf2 ,(r nf1 /r nf2 )is recommended to be less than 100 w . the r clm should be the non-inductive resistor. fig.26 shows the primary and secondary current wave-forms under the current limiting operation. at the typical application of pulse by pulse primary current detecting circuit,the secondary current depends on the primary current.as the peak value of secondary current is limited to specified value,the characteristics curve of output voltage versus output current become to the one as shown in fig.27. (a)in case of feed forward system (2)over current limiting curve i1 i2 r clm clm fig.26 primary and secondary current waveforms under the current limiting operation condition on feed forward system (a) feed forward system i p1 i p2 i1 i2 (b) primary and secondary current
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 18 fig.30 method to control the knee point of frequency drop v out v out v out to make the knee point high to make the knee point low m51996a cvcc vcc fig.29 current to lower frequency during over current r3 soft collector r1 r2 f/b reg photo-coupler for feed back signal reg f/b 500 3k 1s 6s m51996a fig.28 relationship between reg terminal and f/b terminal if the curve becomes vertical because of an excess current, the output voltage is lowered and no feedback current flows from feedback photo-coupler;the pwm comparator operates to enlarge the duty sufficiently,but the signal from the clm+ section operates to make the pulse width narrower. under the condition in which i2 in fig.26 does not become 0,the output voltage is proportional to the product of the input voltage vin(primary side voltage of the main transformer) and on duty.if the bias winding is positive,vcc is approximately proportional to vin.the existance of feed back current of the photo-coupler is known by measuring the f/b terminal voltage which becomes less than 2vbe in the internal circuit of reg terminal and f/b terminal if the output current flows from the f/b terminal. fig.29 shows an application example. q1 is turned on when normal output voltage is controlled at a certain value.the soft terminal is clampedto a high-level voltage.if the output voltage decreases and the curve starts to drop,no feed back current flows,q1 is turned off and the soft terminal responds to the smoothed output voltage. it is recommended to use an r1 and r2 of 10k w ~30k w .an r3 of 20 to 100k w and c of 1000pf to 8200pf should be used. to change the knee point of frequency drop,use the circuit in fig.30. to have a normal soft start function in the circuit in fig.29,use the circuit in fig.31.it is recommended to use an r4 of 10k w . q1 d1 v out bias winding of the main transformer c to output transistor soft soft soft m51996a cvcc vcc fig.31 circuit to use frequency drop during the over current and normal soft start r3 soft collector r1 r2 f/b reg photo-coupler for feed back signal q1 d1 v out bias winding of the main transformer c to output transistor r soft c soft q2 r4 d2 d2
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 19 the dc output voltage of smps depends on the vcc voltage of type m51996a when the polarity of the third winding is negative and the system is fly back.so the operation of type m51996a will stop when the vcc becomes lower than "operation-stop voltage" of m51996a when the dc output voltage of smps decreases under specified value at over load condition. however,the m51996a will non-operate and operate intermittently,as the vcc voltage rises in accordance with the decrease of icc current. the fly back system has the constant output power characteristics as shown in fig.32 when the peak primary current and the operating frequency are constant. toavoid anincrease of the output current,the frequency is lowered when the dc output voltage of smps starts to drop using the soft terminal.vcc is divided and is input to the soft terminal as shown in fig.33,because the voltage in proportional to the output voltage is obtained from the bias winding.in this application example,the current flowing to r3 added to the start- up current.so please use high resistance or 100k w to 200k w for r3. the start-up current is not affected by r3 if r3 is connected to cvcc2 in the circuit shown in fig.20. (b)in case of fly back system
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 20 20 15 10 5 0 0 4 8 12 16 20 total stored gate charge(nc)
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 21 m51996a f/b fig.39 how to get the narrow pulse width during the start of operation to photo coupler 100 w c how to synchronize with external circuit type m51996a has no function to synchronize with external circuit,however,there is some application circuit for synchronization as shown in fig.40. m51996a fig.40 how to synchronize with external circuit synchronous pulse q1 r off c f r on t-on cf t-off 0v 0v
switching regulator control m51996ap/fp mitsubishi (dig./ana. interface) ( / 22 ) 22 the maximum ambient temperature of type m51996a is +85?,however,the ambient temperature in vicinity of the ic is not uniform and varies place by place,as the amount of power dissipation is fearfully large and the power dissipation is generated locally in the switching regulator. so it is one of the good idea to check the ic package temperature. the temperature difference between ic junction and the surface of ic package is 15? or less,when the ic junction temperature is measured by temperature dependency of forward voltage of pin junction,and ic package temperature is measured by "thermo- viewer",and also the ic is mounted on the "phenol-base" pc board in normal atmosphere. so it is concluded that the maximum case temperature(surface temperature of ic) rating is 120? with adequate margin. attention for heat generation

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