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TDA7294 100v - 100w dmos audio amplifier with mute/st-by very high operating voltage range ( 40v) dmos power stage high output power (up to 100w mu- sic power) muting/stand-by functions no switch on/off noise no boucherot cells very low distortion very low noise short circuit protection thermal shutdown description the TDA7294 is a monolithic integrated circuit in multiwatt15 package, intended for use as audio class ab amplifier in hi-fi field applications (home stereo, self powered loudspeakers, top- class tv). thanks to the wide voltage range and to the high out current capability it is able to sup- ply the highest power into both 4 w and 8 w loads even in presence of poor supply regulation, with high supply voltage rejection. the built in muting function with turn on delay simplifies the remote operation avoiding switching on-off noises. february 1996 in- 2 r2 680 w c2 22 m f c1 470nf in+ r1 22k 3 r3 22k - + mute stby 4 vm vstby 10 9 in+mute mute stby r4 22k thermal shutdown s/c protection r5 10k c3 10 m fc410 m f 1 stby-gnd c5 22 m f 713 14 6 15 8 -vs -pwvs bootstrap out +pwvs +vs c9 100nf c8 1000 m f -vs d93au011 +vs c7 100nf c6 1000 m f TDA7294 figure 1: typical application and test circuit multiwatt15 ordering number: TDA7294v multipower bcd technology 1/16
block diagram absolute maximum ratings symbol parameter value unit v s supply voltage (no signal) 50 v i o output peak current 10 a p tot power dissipation t case =70 c50w t op operating ambient temperature range 0 to 70 c t stg ,t j storage and junction temperature 150 c tab connected to -v s pin connection (top view) TDA7294 2/16
thermal data symbol description value unit r th j-case thermal resistance junction-case max 1.5 c/w electrical characteristics (refer to the test circuit v s = 35v, r l =8 w ,g v = 30db; r g =50 w ;t amb =25 c, f = 1 khz; unless otherwise specified. symbol parameter test condition min. typ. max. unit v s supply range 10 40 v i q quiescent current 20 30 60 ma i b input bias current 500 na v os input offset voltage +10 mv i os input offset current +100 na p o rms continuous output power d = 0.5%: v s = 35v, r l =8 w v s = 31v, r l =6 w v s = 27v, r l =4 w 60 60 60 70 70 70 w w w music power (rms) iec268.3 rules - d t = 1s (*) d = 10% r l =8 w ;v s = 38v r l =6 w ;v s = 33v r l =4 w ;v s = 29v (***) 100 100 100 w w w d total harmonic distortion (**) p o = 5w; f = 1khz p o = 0.1 to 50w; f = 20hz to 20khz 0.005 0.1 % % v s = 27v, r l =4 w: p o = 5w; f = 1khz p o = 0.1 to 50w; f = 20hz to 20khz 0.01 0.1 % % sr slew rate 7 10 v/ m s g v open loop voltage gain 80 db g v closed loop voltage gain 24 30 40 db e n total input noise a = curve f = 20hz to 20khz 1 25 m v m v f l ,f h frequency response (-3db) p o = 1w 20hz to 20khz r i input resistance 100 k w svr supply voltage rejection f = 100hz; v ripple = 0.5vrms 60 75 db t s thermal shutdown 145 c stand-by function (ref: -v s or gnd) v st on stand-by on threshold 1.5 v v st off stand-by off threshold 3.5 v att st-by stand-by attenuation 70 90 db i q st-by quiescent current @ stand-by 1 3 ma mute function (ref: -v s or gnd) v mon mute on threshold 1.5 v v moff mute off threshold 3.5 v att mute mute attenuation 60 80 db note (*): music power concept music power is the maximal power which the amplifier is capable of producing across the rated load resistance (regardless of non linearity) 1 sec after the application of a sinusoidal input signal of frequency 1khz. note (**): tested with optimized application board (see fig. 2) note (***): limited by the max. allowable current. TDA7294 3/16
figure 2: p.c.b. and components layout of the circuit of figure 1. (1:1 scale) note: the stand-by and mute functions can be referred either to gnd or -vs. on the p.c.b. is possible to set both the configuration through the jumper j1. TDA7294 4/16
application suggestions (see test and application circuits of the fig. 1) the recommended values of the external components are those shown on the application circuit of fig- ure 1. different values can be used; the following table can help the designer. components suggested value purpose larger than suggested smaller than suggested r1 (*) 22k input resistance increase input imprdance decrease input impedance r2 680 w closed loop gain set to 30db (**) decrease of gain increase of gain r3 (*) 22k increase of gain decrease of gain r4 22k st-by time constant larger st-by on/off time smaller st-by on/off time; pop noise r5 10k mute time constant larger mute on/off time smaller mute on/off time c1 0.47 m f input dc decoupling higher low frequency cutoff c2 22 m f feedback dc decoupling higher low frequency cutoff c3 10 m f mute time constant larger mute on/off time smaller mute on/off time c4 10 m f st-by time constant larger st-by on/off time smaller st-by on/off time; pop noise c5 22 m f bootstrapping signal degradation at low frequency c6, c8 1000 m f supply voltage bypass danger of oscillation c7, c9 0.1 m f supply voltage bypass danger of oscillation (*) r1 = r3 for pop optimization (**) closed loop gain has to be 24db TDA7294 5/16
figure 3: output power vs. supply voltage. figure 5: output power vs. supply voltage figure 4: distortion vs. output power figure 8: distortion vs. frequency typical characteristics (application circuit of fig 1 unless otherwise specified) figure 6: distortion vs. output power figure 7: distortion vs. frequency TDA7294 6/16
figure 14: power dissipation vs. output power figure 13: power dissipation vs. output power figure 11: mute attenuation vs. v pin10 figure 12: st-by attenuation vs. v pin9 figure 10: supplyvoltage rejection vs. frequency typical characteristics (continued) figure 9: quiescent current vs. supply voltage TDA7294 7/16
introduction in consumer electronics, an increasing demand has arisen for very high power monolithic audio amplifiers able to match, with a low cost the per- formance obtained from the best discrete de- signs. the task of realizing this linear integrated circuit in conventional bipolar technology is made ex- tremely difficult by the occurence of 2nd break- down phenomenon. it limits the safe operating area (soa) of the power devices, and as a con- sequence, the maximum attainable output power, especially in presence of highly reactive loads. moreover, full exploitation of the soa translates into a substantial increase in circuit and layout complexity due to the need for sophisticated pro- tection circuits. to overcome these substantial drawbacks, the use of power mos devices, which are immune from secondary breakdown is highly desirable. the device described has therefore been devel- oped in a mixed bipolar-mos high voltage tech- nology called bcd 100. 1) output stage the main design task one is confronted with while developing an integrated circuit as a power op- erational amplifier, independently of the technol- ogy used, is that of realizing the output stage. the solution shown as a principle shematic by fig 15 represents the dmos unity-gain output buffer of the TDA7294. this large-signal, high-power buffer must be ca- pable of handling extremely high current and volt- age levels while maintaining acceptably low har- monic distortion and good behaviour over fre- quency response; moreover, an accurate control of quiescent current is required. a local linearizing feedback, provided by differen- tial amplifier a, is used to fullfil the above require- ments, allowing a simple and effective quiescent current setting. proper biasing of the power output transistors alone is however not enough to guarantee the ab- sence of crossover distortion. while a linearization of the dc transfer charac- teristic of the stage is obtained, the dynamic be- haviour of the system must be taken into account. a significant aid in keeping the distortion contrib- uted by the final stage as low as possible is pro- vided by the compensation scheme, which ex- ploits the direct connection of the miller capacitor at the amplifier's output to introduce a local ac feedback path enclosing the output stage itself. 2) protections in designing a power ic, particular attention must be reserved to the circuits devoted to protection of the device from short circuit or overload condi- tions. due to the absence of the 2nd breakdown phe- nomenon, the soa of the power dmos transis- tors is delimited only by a maximum dissipation curve dependent on the duration of the applied stimulus. in order to fully exploit the capabilities of the power transistors, the protection scheme imple- mented in this device combines a conventional soa protection circuit with a novel local tempera- ture sensing technique which o dynamicallyo con- trols the maximum dissipation. figure 15: principle schematic of a dmos unity-gain buffer. TDA7294 8/16
in addition to the overload protection described above, the device features a thermal shutdown circuit which initially puts the device into a muting state (@ tj = 145 o c) and then into stand-by (@ tj = 150 o c). full protection against electrostatic discharges on every pin is included. 3) other features the device is provided with both stand-by and mute functions, independently driven by two cmos logic compatible input pins. the circuits dedicated to the switching on and off of the amplifier have been carefully optimized to avoid any kind of uncontrolled audible transient at the output. the sequence that we recommend during the on/off transients is shown by figure 16. the application of figure 17 shows the possibility of using only one command for both st-by and mute functions. on both the pins, the maximum applicable range corresponds to the operating supply voltage. 1n4148 10k 30k 20k 10 m f 10 m f mute stby d93au014 mute/ st-by figure 17: single signal st-by/mute control circuit play off st-by mute mute st-by off d93au013 5v 5v +vs (v) +35 -35 v mute pin #10 (v) v st-by pin #9 (v) -vs v in (mv) i p (ma) v out (v) figure 16: turn on/off suggested sequence TDA7294 9/16
TDA7294 3 1 4 13 7 815 2 14 6 10 r3 680 c11 22 m f l3 5 m h 270 r16 13k c15 22 m f 9 r16 13k c13 10 m f r13 20k c11 330nf r15 10k c14 10 m f r14 30k d5 1n4148 play st-by 270 l1 1 m h t1 bdx53a t3 bc394 d3 1n4148 r4 270 r5 270 t4 bc393 t5 bc393 r6 20k r7 3.3k c16 1.8nf r8 3.3k c17 1.8nf z2 3.9v z1 3.9v l2 1 m h 270 d4 1n4148 d2 byw98100 r1 2 r2 2 c9 330nf c10 330nf t2 bdx54a t6 bc393 t7 bc394 t8 bc394 r9 270 r10 270 r11 29k out in c7 100nf c5 1000 m f c8 100nf c6 1000 m f c1 1000 m f c2 1000 m f c3 100nf c4 100nf +40v +20v d1 byw98100 gnd -20v -40v d93au016 figure 18: high efficiency application circuit application information high-efficiency constraints of implementing high power solutions are the power dissipation and the size of the power supply. these are both due to the low effi- ciency of conventional ab class amplifier ap- proaches. here below (figure 18) is described a circuit pro- posal for a high efficiency amplifier which can be adopted for both hi-fi and car-radio applica- tions. the TDA7294 is a monolithic mos power ampli- fier which can be operated at 80v supply voltage (100v with no signal applied) while delivering out- put currents up to 10 a. this allows the use of this device as a very high power amplifier (up to 180w as peak power with t.h.d.=10 % and rl = 4 ohm); the only drawback is the power dissipation, hardly manageable in the above power range. figure 20 shows the power dissipation versus output power curve for a class ab amplifier, com- pared with a high efficiency one. in order to dimension the heatsink (and the power supply), a generally used average output power value is one tenth of the maximum output power at t.h.d.=10 %. from fig. 20, where the maximum power is around 200 w, we get an average of 20 w, in this condition, for a class ab amplifier the average power dissipation is equal to 65 w. the typical junction-to-case thermal resistance of the TDA7294 is 1 o c/w (max= 1.5 o c/w). to avoid that, in worst case conditions, the chip tem- perature exceedes 150 o c, the thermal resistance of the heatsink must be 0.038 o c/w (@ max am- bient temperature of 50 o c). as the above value is pratically unreachable; a high efficiency system is needed in those cases where the continuous rms output power is higher than 50-60 w. the TDA7294 was designed to work also in higher efficiency way. for this reason there are four power supply pins: two intended for the signal part and two for the power part. t1 and t2 are two power transistors that only op- erate when the output power reaches a certain threshold (e.g. 20 w). if the output power in- creases, these transistors are switched on during the portion of the signal where more output volt- age swing is needed, thus obootstrappingo the power supply pins (#13 and #15). the current generators formed by t4, t7, zener TDA7294 10/16
figure 19: p.c.b. and components layout of the circuit of figure 18 (1:1 scale) diodes z1,z2 and resistors r7,r8 define the mini- mum drop across the power mos transistors of the TDA7294. l1, l2, l3 and the snubbers c9, r1 and c10, r2 stabilize the loops formed by the obootstrapo circuits and the output stage of the TDA7294. in figures 21,22 the performances of the system in terms of distortion and output power at various frequencies (measured on pcb shown in fig. 19) are displayed. the output power that the TDA7294 in high- efficiency application is able to supply at vs = +40v/+20v/-20v/-40v; f =1 khz is: - pout = 150 w @ t.h.d.=10 % with rl= 4 ohm - pout = 120 w @ o = 1 % o o o - pout = 100 w @ o =10 % with rl= 8 ohm - pout = 80 w @ o = 1 % o o o results from efficiency measurements (4 and 8 ohm loads, vs = 40v) are shown by figures 23 and 24. we have 3 curves: total power dissipa- tion, power dissipation of the TDA7294 and power dissipation of the darlingtons. by considering ag ain a maximum average output power (music signal) of 20w, in case of the high efficiency application, the thermal resistance value needed from the heatsink is 2.2 o c/w (vs = 40 v and rl= 4 ohm). all components (TDA7294 and power transistors t1 and t2) can be placed on a 1.5 o c/w heatsink, with the power darlingtons electrically insulated from the heatsink. since the total power dissipation is less than that of a usual class ab amplifier, additional cost sav- ings can be obtained while optimizing the power supply, even with a high headroom. TDA7294 11/16
figure 21: distortion vs. output power figure 20: power dissipation vs. output power figure 23: power dissipation vs. output power figure 22: distortion vs. output power figure 24: power dissipation vs. output power high-efficiency TDA7294 12/16
bridge application another application suggestion is the bridge configuration, where two TDA7294 are used, as shown by the schematic diagram of figure 25. in this application, the value of the load must not be lower than 8 ohm for dissipation and current capability reasons. a suitable field of application includes hi-fi/tv subwoofers realizations. the main advantages offered by this solution are: - high power performances with limited supply voltage level. - considerably high output power even with high load values (i.e. 16 ohm). the characteristics shown by figures 27 and 28, measured with loads respectively 8 ohm and 16 ohm. with rl= 8 ohm, vs = 25v the maximum output power obtainable is 150 w, while with rl=16 ohm, vs = 35v the maximum pout is 170 w. 22k 0.56 m f 2200 m f 0.22 m f TDA7294 + - 22 m f 22k 680 22k 3 1 4 13 7 +vs vi 8 15 2 14 6 10 9 + - 3 0.56 m f 22k 1 4 2 14 6 22 m f 22k 680 10 9 22 m f 15 8 -vs 2200 m f 0.22 m f 22 m f 20k 10k 30k 1n4148 st-by/mute TDA7294 13 7 d93au015a figure 25: bridge application circuit TDA7294 13/16
figure 27: distortion vs. output power figure 26: frequency response of the bridge application figure 28: distortion vs. output power TDA7294 14/16
dim. mm inch min. typ. max. min. typ. max. a 5 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 1.14 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 22.1 22.6 0.870 0.890 l1 22 22.5 0.866 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 4.2 4.3 4.6 0.165 0.169 0.181 m1 4.5 5.08 5.3 0.177 0.200 0.209 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 package mechanical data (vertical) TDA7294 15/16
information furnished is believed to be accurate and reliable. however, sgs-thomson microelectronics assumes no responsibility for the consequences 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 sgs-thomson microelectronics. specifications men- tioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in life support devices or systems without ex- press written approval of sgs-thomson microelectronics. ? 1996 sgs-thomson microelectronics all rights reserved sgs-thomson microelectronics group of companies australia - brazil - france - germany - hong kong - italy - japan - korea - malaysia - malta - morocco - the netherlands - singapore - spain - sweden - switzerland - taiwan - thaliand - united kingdom - u.s.a. TDA7294 16/16

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