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L296 L296p june 2000 high current switching regulators . 4 a output current . 5.1 v to 40 v output voltage range . 0 to 100 % duty cycle range . precise ( 2 %) on-chip reference . switching frequency up to 200 khz . very high efficiency (up to 90 %) . very few external components . soft start . reset output . external programmable limiting current (L296p) . control circuit for crowbar scr . input for remote inhibit and synchronus pwm . thermal shutdown description the L296 andL296p are stepdownpower switching regulators delivering 4 a at a voltage variable from 5.1 v to 40 v. featuresof the devices includesoft start, remotein- hibit, thermal protection, a reset output for micro- processors and a pwm comparator input for syn- chronization in multichip configurations. the L296p incudes external programmable limiting current. the L296 and L296p are mounted in a 15-lead mul- tiwatt ? plasticpowerpackageand requiresvery few external components. efficient operation at switching frequencies up to 200 khz allows a reduction in the size and cost of external filter components. a voltage sense input and scr drive output are provided for optional crowbar overvoltage protection with an external scr. multiwatt ? (15 lead) ordering numbers : L296 (vertical) L296ht (horizontal) L296p (vertical) L296pht (horizontal) pin connection (top view) ? 1/22
pin functions n name function 1 crowbar input voltage sense input for crowbar overvoltage protection. normally connected to the feedback input thus triggering the scr when v out exceeds nominal by 20 %. may also monitor the input and a voltage divider can be added to increase the threshold. connected to ground when scr not used. 2 output regulator output 3 supply voltage unrergulated voltage input. an internal regulator powers the L296s internal logic. 4 current limit a resistor connected between this terminal and ground sets the current limiter threshold. if this terminal is left unconnected the threshold is internally set (see electrical characteristics). 5 soft start soft start time constant. a capacitor is connected between this terminal and ground to define the soft start time constant. this capacitor also determines the average short circuit output current. 6 inhibit input ttl level remote inhibit. a logic high level on this input disables the device. 7 sync input multiple L296s are synchronized by connecting the pin 7 inputs together and omitting the oscillator rc network on all but one device. 8 ground common ground terminal 9 frequency compensation a series rc network connected between this terminal and ground determines the regulation loop gain characteristics. 10 feedback input the feedback terminal on the regulation loop. the output is connected directly to this terminal for 5.1v operation ; it is connected via a divider for higher voltages. 11 oscillator a parallel rc networki connected to this terminal determines the switching frequency. this pin must be connected to pin 7 input when the internal oscillator is used. 12 reset input input of the reset circuit. the threshold is roughly 5 v. it may be connected to the feedback point or via a divider to the input. 13 reset delay a capacitor connected between this terminal and ground determines the reset signal delay time. 14 reset output open collector reset signal output. this output is high when the supply is safe. 15 crowbar output scr gate drive output of the crowbar circuit. block diagram L296 - L296p 2/22
circuit operation (refer to the block diagram) the L296 and L296p are monolithic stepdown switching regulators providing output voltages from 5.1v to 40v and delivering 4a. the regulationloop consists of a sawtoothoscillator, error amplifier, comparatorand the outputstage. an error signal is produced by comparing the output voltage with a precise 5.1v on-chipreference(zener zap trimmed to 2 %). this error signalis then com- pared with the sawtooth signal to generate the fixed frequencypulse width modulatedpulseswhich drive the output stage.the gain and frequencystability of the loop can be adjusted by an externalrc network connectedto pin9. closing the loop directlygives an outputvoltageof 5.1v.higher voltagesare obtained by inserting a voltage divider. output overcurrents at switch on are prevented by the soft start function. the error amplifier output is initially clamped by the external capacitor css and allowed to rise, linearly, as this capacitor is charged by a constant current source. outputoverloadprotection is provided in the form of a current limiter. the load current is sensed by an internal metal resistor connected to a comparator. when the load current exceeds a preset threshold this comparator sets a flip flop which disables the outputstage and discharges the soft start capacitor. a second comparator resets the flip flop when the voltage across the soft start capacitor has fallen to 0.4v. the output stage is thus re-enabled and the output voltage rises under control of the soft start network. if the overload condition is still present the limiter will trigger again when the threshold current is reached. the average short circuit current is lim- ited to a safe value by the dead time introduced by the soft start network. the reset circuit generates an output signal when the supply voltage exceeds a threshold pro- grammed by an external divider. the reset signal is generated with a delay time programmed by an ex- ternal capacitor. when the supply falls below the threshold the reset output goes low immediately. the reset output is an open collector. the scrowbar circuit senses the output voltage and the crowbar output can provide a current of 100ma to switch on an externalscr. this scr is triggered when the output voltage exceeds the nominal by 20%. there is no internal connection between the outputand crowbar sense input thereforethe crow- bar can monitor either the input or the output. a ttl - level inhibit input is provided for applications such as remote on/offcontrol. this input is activated by high logic level and disables circuit operation.af- ter an inhibit the L296 restarts under control of the soft start network. the thermal overload circuit disables circuit opera- tion when the junction temperature reaches about 150 c and has hysteresis to prevent unstable con- ditions. figure 1 : reset output waveforms L296 - L296p 3/22
figure 2 : soft start waveforms figure 3 : current limiter waveforms absolute maximum ratings symbol parameter value unit v i input voltage (pin 3) 50 v v i v 2 input to output voltage difference 50 v v 2 output dc voltage output peak voltage at t = 0.1 m sec f = 200khz 1 7 v v v 1 ,v 12 voltage at pins 1, 12 10 v v 15 voltage at pin 15 15 v v 4 ,v 5 ,v 7 ,v 9 ,v 13 voltage at pins 4, 5, 7, 9 and 13 5.5 v v 10 ,v 6 voltage at pins 10 and 6 7 v v 14 voltage at pin 14 (i 14 1 ma) v i i 9 pin 9 sink current 1 ma i 11 pin 11 source current 20 ma i 14 pin 14 sink current (v 14 < 5 v) 50 ma p tot power dissipation at t case 90 c20w t j ,t stg junction and storage temperature 40 to 150 c L296 - L296p 4/22
thermal data symbol parameter value unit r th j-case thermal resistance junction-case max. 3 c/w r th j-amb thermal resistance junction-ambient max. 35 c/w electrical characteristics (refer to the test circuits t j =25 o c, v i = 35v, unless otherwise specified) symbol parameter test conditions min. typ. max. unit fig. dynamic characteristics (pin 6 to gnd unless otherwise specified) v o output voltage range v i = 46v, i o =1a v ref 40 v 4 v i input voltage range v o =v ref to 36v, i o 3a 9 46 v 4 v i input voltage range note (1), v o =v ref to 36v i o =4a 46 v 4 d v o line regulation v i =10v to 40v, v o =v ref ,i o =2a 15 50 mv 4 d v o load regulation v o =v ref i o =2ato4a i o = 0.5a to 4a 10 15 30 45 mv 4 v ref internal reference voltage (pin 10) v i = 9v to 46v, i o = 2a 5 5.1 5.2 v 4 d v ref d t average temperature coefficient of reference voltage t j =0 c to 125 c, i o = 2a 0.4 mv/ c v d dropout voltage between pin 2 and pin 3 i o =4a i o =2a 2 1.3 3.2 2.1 v v 4 4 i 2l current limiting threshold (pin 2) L296 - pin 4 open, v i = 9v to 40v, v o =v ref to 36v 4.5 7.5 a 4 L296p - v i = 9v to 40v, v o =v ref pin 4 open r iim = 22k w 5 2.5 7 4.5 a4 i sh input average current v i = 46v, output short-circuited 60 100 ma 4 h efficiency i o =3a v o =v ref v o = 12v 75 85 %4 svr supply voltage ripple rejection d v i =2v rms ,f ripple = 100hz v o =v ref ,i o =2a 50 56 db 4 f switching frequency 85 100 115 khz 4 d f d v i voltage stability of switching frequency v i = 9v to 46v 0.5 % 4 d f d t j temperature stability of switching frequency t j =0 c to 125 c1%4 f max maximum operating switching frequency v o =v ref ,i o = 1a 200 khz t sd thermal shutdown junction temperature note (2) 135 145 c dc characteristics i 3q quiescent drain current v i = 46v, v 7 = 0v, s1 : b, s2 : b v 6 =0v v 6 =3v 66 30 85 40 ma i 2l output leakage current v i = 46v, v 6 = 3v, s1 : b, s2 : a, v 7 =0v 2ma note (1) : using min. 7 a schottky diode. (2) : guaranteed by design, not 100 % tested in production. L296 - L296p 5/22
electrical characteristics (continued) symbol parameter test conditions min. typ. max. unit fig. soft start i 5so source current v 6 = 0v, v 5 = 3v 80 130 150 m a6b i 5si sink current v 6 = 3v, v 5 = 3v 50 70 120 m a6b inhibit v 6l v 6h input voltage low level high level v i = 9v to 46v, v 7 = 0v, s1 : b, s2 : b 0.3 2 0.8 5.5 v6a i 6l i 6h input current with input voltage low level high level v i = 9v to 46v, v 7 = 0v, s1 : b, s2 : b v 6 = 0.8v v 6 =2v 10 3 m a6a error amplifier v 9h high level output voltage v 10 = 4.7v, i 9 = 100 m a, s1 : a, s2 : a 3.5 v 6c v 9l low level output voltage v 10 = 5.3v, i 9 = 100 m a, s1 : a, s2 : e 0.5 v 6c i 9si sink output current v 10 = 5.3v, s1 : a, s2 : b 100 150 m a6c i 9so source output current v 10 = 4.7v, s1 : a, s2 : d 100 150 m a6c i 10 input bias current v 10 = 5.2v, s1 : b v 10 = 6.4v, s1 : b, L296p 2 2 10 10 m a m a 6c 6c g v dc open loop gain v 9 = 1v to 3v, s1 : a, s2 : c 46 55 db 6c oscillator and pwm comparator i 7 input bias current of pwm comparator v 7 = 0.5v to 3.5v 5 m a6a i 11 oscillator source current v 11 = 2v, s1 : a, s2 : b 5 ma reset v 12 r rising threshold voltage v i = 9v to 46v, s1 : b, s2 : b v ref -150mv v ref -100mv v ref -50mv v6d v 12 f falling threshold voltage 4.75 v ref -150mv v ref -100mv v6d v 13 d delay thershold voltage v 12 = 5.3v, s1 : a, s2 : b 4.3 4.5 4.7 v 6d v 13 h delay threshold voltage hysteresis 100 mv 6d v 14 s output saturation voltage i 14 = 16ma, v 12 = 4.7v, s1, s2 : b 0.4 v 6d i 12 input bias current v 12 =0vtov ref , s1 : b, s2 : b 1 3 m a6d i 13 so i 13 si delay source current delay sink current v 13 = 3v, s1 : a, s2 : b v 12 = 5.3v v 12 = 4.7v 70 10 110 140 m a ma 6d i 14 output leakage current v i = 46v, v 12 = 5.3v, s1 : b, s2 : a 100 m a6d crowbar v 1 input threshold voltage s1 : b 5.5 6 6.4 v 6b v 15 output saturation voltage v i = 9v to 46v, v i = 5.4v, i 15 = 5ma, s1 : a 0.2 0.4 v 6b i 1 input bias current v 1 = 6v, s1 : b 10 m a6b i 15 output source current v i = 9v to 46v, v 1 = 6.5v, v 15 = 2v, s1 : b 70 100 ma 6b L296 - L296p 6/22
figure 4 : dynamic test circuit c7, c8 : ekr (roe) l1 : l = 300 m h at 8 a core type : magnetics 58930 - a2 mpp n turns : 43 wire gauge : 1 mm (18 awg) cogema 946044 (*) minimum suggested value (10 m f) to avoid oscillations. ripple consideration leads to typical value of 1000 m f or higher. figure 5 : pc. board and component layout of the circuit of figure 4 (1:1 scale) L296 - L296p 7/22
figure 6 : dc test circuits. figure 6a. figure 6b. figure 6c. figure 6d. 1 - set v 10 for v 9 =1v 2 - change v 10 to obtain v 9 =3v 3-g v = dv 9 = 2v d v 10 d v 10 L296 - L296p 8/22
figure 7 : quienscentdrain current vs. supply voltage (0 % duty cycle - see fig. 6a). figure 8 : quienscentdrain current vs. supply voltage (100 % duty cycle see fig. 6a). figure 9 : quiescent drain current vs. junction temperature (0 % duty cycle - see fig. 6a). figure 10 : quiescentdrain current vs. junction temperature (100 % duty cycle - see fig. 6a). figure 11 : reference voltage (pin 10) vs. v i (see fig. 4). figure 12 : referencevoltage (pin 10) vs. junction temperature (see fig. 4). L296 - L296p 9/22
figure 13 : open loop frequency and phase response of error amplifier (see fig. 6c). figure 14 : switching frequency vs. input voltage (see fig. 4). figure 15 : switching frequency vs. junction temperature (see fig. 4). figure 16 : switching frequency vs. r1 (see fig. 4). figure 17 : line transient response (see fig. 4). figure 18 : load transient response (see fig. 4). L296 - L296p 10/22
figure 19 : supplyvoltage ripple rejection vs. frequency (see fig. 4). figure 20 : dropout voltage between pin 3 and pin 2 vs. current at pin 2. figure 21 : dropout voltage between pin 3 and pin 2 vs. junction temperature. figure 22 : power dissipation derating curve. figure 23 : power dissipation (device only) vs. input voltage. figure 24 : power dissipation (device only) vs. input voltage. L296 - L296p 11/22
figure 25 : power dissipation (device only) vs. outputvoltage (see fig. 4). figure 26 : power dissipation (device only) vs. output voltage (see fig. 4). figure 28 : efficiency vs. output current. figure 29 : efficiency vs. output voltage. figure 30 : efficiency vs. output voltage. figure27 : voltageand current waveformsat pin 2 (see fig. 4). L296 - L296p 12/22
figure 31 : current limiting threshold vs. r pin 4 (L296p only). figure 32 : current limiting threshold vs. junction temperature. figure 33 : current limiting threshold vs. supply voltage. L296 - L296p 13/22
application information figure 34 : typical application circuit. (*) minimum value (10 m f) to avoid oscillations ; ripple consideration leads to typical value of 1000 m f or higher l1 : 58930 - mpp cogema 946044 ; gup 20 cogema 946045 suggested inductor (l1) core type no turns wire gauge air gap magnetics 58930 a2mpp 43 1.0 mm thomson gup 20 x 16 x 7 65 0.8 mm 1 mm siemens ec 35/17/10 (b6633& g0500 x127) 40 2 x 0.8 mm vogt 250 m h toroidal coil, part number 5730501800 resistor values for standard output voltages v 0 r8 r7 12 v 15 v 18 v 24 v 4.7 k w 4.7 k w 4.7 k w 4.7 k w 6.2 k w 9.1 k w 12 k w 18 k w L296 - L296p 14/22
figure 35 : p.c. board and component layout of the circuit of fig. 34 (1:1 scale) selection of component values (see fig. 34) component recommended value purpose allowed rage notes min. max. r1 r2 100 k w set input voltage threshold for reset. 220k w r1/r2 v i min 5 - 1 if output voltage is sensed r1 and r2 may be limited and pin 12 connected to pin 10. r3 4.3 k w sets switching frequency 1 k w 100k w r4 10 k w pull-down resistor 22k w may be omitted and pin 6 grounded if inhibit not used. r5 15 k w frequency compensation 10k w r6 collector load for reset output v o 0.05a omitted if reset function not used. r7 r8 4.7 k w divider to set output voltage 1k w r7/r8 = v o - v ref v ref - r iim sets current limit level 7.5k w if r iim is omitted and pin 4 left open the current limit is internally fixed. c1 10 m f stability 2.2 m f c2 2.2 m f sets reset delay omitted if reset function not used. c3 2.2 nf sets switching frequency 1 nf 3.3nf c4 2.2 m f soft start 1 m f also determines average short circuit current. c5 33 nf frequency compensation c6 390 pf high frequency compensation not required for 5 v operation. c7, c8 l1 100 m f 300 m h output filter 100 m h q1 crowbar protection the scr must be able to withstand the peak discharge current of the output capacitor and the short circuit current of the device. d1 recirculation diode 7a schottky or 35 ns t rr diode. L296 - L296p 15/22
figure 36 : a minimal 5.1 v fixed regulator. very few components are required. figure 37 : 12 v/10 a power supply. L296 - L296p 16/22
figure 38 : programmable power supply. v o = 5.1 to 15 v i o = 4 a max. (min. load current = 100 ma) ripple 20 mv load regulation (1 a to 4 a) = 10 mv (v o = 5.1 v) line regulation (220 v 15 % and to i o = 3 a) = 15 mv (v o = 5.1 v) figure 39 : preregulator for distributed supplies. (*) l2 and c2 are necessary to reduce the switching frequency spikes. L296 - L296p 17/22
figure 40 : in multiple supplies several L296s can be synchronized as shown. figure 41 : voltage sensing for remote load. figure 42 : a 5.1 v/15 v/24 v multiple supply. note the synchronization of the three L296s. L296 - L296p 18/22
figure 43 : 5.1v/2a power supply using external limiting current resistor and crow- bar protection on the supply voltage (L296p only) soft-start and repetitive power-on when the device is repetitivelypowered-on,the soft- start capacitor, c ss , must be discharged rapidly to ensurethat each start is osofto. this can be achieved economicallyusing the reset circuit, as shownin fig- ure 44. in this circuit the divider r1, r2 connectedto pin 12 determines the minimum supply voltage, below which the open collector transistor at the pin 14 out- put discharges c ss . figure 44 figure 45 figure 46 the approximate discharge times obtainedwith this circuit are : css ( m f) tdis ( m s) 2.2 4.7 10 200 300 600 if thesetimes are still too long,an externalpnptran- sistor may be added, as shown in figure 45 ; with this circuit discharge times of a few microseconds may be obtained. how to obtain both reset and power fail figure 46 illustrateshowit is possibleto obtainat the same time both the power fail and reset functions simply by adding one diode(d) and one resistor (r). in this case the reset delay time (pin 13) can only start when the output voltage is v o v ref - 100mv and the voltage accross r2 is higher than 4.5v. with the hysteresis resistor it is possible to fix the in- put pin 12 hysteresis in order to increase immunity to the 100hz ripple present on the supply voltage. moreover, the power fail and reset delay time are automatically locked to the soft-start. soft-start and delayed reset are thus two sequential functions. the hysteresis resistor should be in the range of aboit 100k w and the pull-up resistor of 1 to 2.2k w . L296 - L296p 19/22
multiwatt15 v dim. mm inch min. typ. max. min. typ. max. a5 0.197 b 2.65 0.104 c 1.6 0.063 d 1 0.039 e 0.49 0.55 0.019 0.022 f 0.66 0.75 0.026 0.030 g 1.02 1.27 1.52 0.040 0.050 0.060 g1 17.53 17.78 18.03 0.690 0.700 0.710 h1 19.6 0.772 h2 20.2 0.795 l 21.9 22.2 22.5 0.862 0.874 0.886 l1 21.7 22.1 22.5 0.854 0.870 0.886 l2 17.65 18.1 0.695 0.713 l3 17.25 17.5 17.75 0.679 0.689 0.699 l4 10.3 10.7 10.9 0.406 0.421 0.429 l7 2.65 2.9 0.104 0.114 m 4.25 4.55 4.85 0.167 0.179 0.191 m1 4.63 5.08 5.53 0.182 0.200 0.218 s 1.9 2.6 0.075 0.102 s1 1.9 2.6 0.075 0.102 dia1 3.65 3.85 0.144 0.152 outline and mechanical data L296 - L296p 20/22
dim. mm inch min. typ. max. min. typ. max. a5 0.197 b 2.65 0.104 c 1.6 0.063 e 0.49 0.55 0.019 0.022 f 0.66 0.75 0.026 0.030 g 1.14 1.27 1.4 0.045 0.050 0.055 g1 17.57 17.78 17.91 0.692 0.700 0.705 h1 19.6 0.772 h2 20.2 0.795 l 20.57 0.810 l1 18.03 0.710 l2 2.54 0.100 l3 17.25 17.5 17.75 0.679 0.689 0.699 l4 10.3 10.7 10.9 0.406 0.421 0.429 l5 5.28 0.208 l6 2.38 0.094 l7 2.65 2.9 0.104 0.114 s 1.9 2.6 0.075 0.102 s1 1.9 2.6 0.075 0.102 dia1 3.65 3.85 0.144 0.152 multiwatt15 h outline and mechanical data L296 - L296p 21/22
information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the conse- quences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specification mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmi- croelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of stmicroelectronics. the st logo is a registered trademark of stmicroelectronics ? 2000 stmicroelectronics printed in italy all rights reserved stmicroelectronics group of companies australia - brazil - china - finland - france - germany - hong kong - india - italy - japan - malaysia - malta - morocco - singapore - spain - sweden - switzerland - united kingdom - u.s.a. http://www.st.com L296 - L296p 22/22

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