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TDA7374B dual bridge audio amplifier for car radio minimum external component count no bootstrap capacitors no boucherot cells clip detector output high output power fixed gain very low stand-by current (1 m a typ) no switch on/off noise protections: output ac/dc short circuit to gnd and to v s very inductive loads overrating chip temperature load dump voltage fortuitous open gnd reverse battery esd description the TDA7374B is a new technology class ab audio dual bridge power amplifier in multiwatt package designed for car radio applications. thanks to the fully complementary pnp/npn out- put configuration the high power performances of the TDA7374B are obtained without bootstrap ca- pacitors. april 1995 test and application circuit multiwatt15 ordering numbers: TDA7374Bv 1/13
pin connection (top view) absolute maximum ratings symbol parameter value unit v s dc supply voltage 28 v v op operating supply voltage 18 v v peak peak supply voltage (t = 50ms) 50 v i o output peak current (not rep. t = 100 m s) 4.5 a i o output peak current (rep. f > 10hz) 3.5 a p tot power dissipation (t case = 85 c) 36 w t stg , t j storage and junction temperature -40 to 150 c thermal data symbol description value unit r th j-case thermal resistance junction-case max 1.8 c/w TDA7374B 2/13
electrical characteristics (refer to the test circuit; v s = 14.4v; r l = 4 w , t amb = 25c, f = 1khz, unless otherwise specified) symbol parameter test condition min. typ. max. unit v s supply range 8 18 v i d total quiescent drain current r l = 150 ma p o output power r l = 4 w ; thd = 10% 17 21 w d distortion r l = 4 w p o = 0.1 to 10w 0.5 % ct cross-talk f = 1khz f = 10khz 65 55 db db r in input impedance 10 k w g v voltage gain 26 db g v voltage gain match. 1 db e in input noise voltage r g = 0 to 10k w weight a 22hz to 22khz 3.5 10 m v m v svr supply voltage rejection r g = 0; f = 100hz f = 10khz 48 55 db asb stand-by attenuation 60 db i sb st-by current 1 m a v sb on st-by on threshold voltage 1.5 v v sb off st-by off threshold voltage 3.5 v v os output offset voltage 200 mv i cd off clipping detector "off" output average current thd = 1% (*) 100 m a i cd on clipping detector "on" output average current thd = 10% (*) 190 m a (*) pin 10 pulled-up to 5v with 10k w ; r l = 4 w TDA7374B 3/13
test and application circuit p.c. board and component layout (1:1 scale) b TDA7374B 4/13
figure 1: quiescent drain current vs. supply voltage figure 2: quiescent output voltage vs. supply voltage figure 3: output power vs. supply voltage figure 5: output power vs. frequency figure 4: distortion vs. output power figure 6: supply voltage rejection vs. frequency for a different values of c6 capacitor r g TDA7374B 5/13
figure 7: cross-talk vs. frequency figure 9: stand-by attenuation vs. threshold voltage figure 8: en input vs. rg figure 11: clipping detector average current (pin 10) vs. distortion figure 12: total power dissipation and efficiency vs. output power figure 10: stand-by attenuation vs. input voltage r g r g TDA7374B 6/13
output stage the fully complementary output stage was made possible by the development of a new compo- nent: the st exclusive power icv pnp. a novel design based upon the connection shown in fig. 13 has then allowed the full exploitation of its possibilities. the clear advantages this new approach has over classical output stages are as follows: 1 - rail-to-rail output voltage swing with no need of bootstrap capacitors. the output swing is limited only by the vcesat of the output transistors, which are in the range of 0.6 ohm each. classical solutions adopting composite pnp-npn for the upper output stage have higher saturation loss on the top side of the waveform. this unbal- anced saturation causes a significant power re- duction. the only way to recover power consists of the addition of expensive bootstrap capacitors. 2 - absolute stability without any external compensation. referring to the circuit of fig. 13 the gain v out /v in is greater than unity, approximately 1 + r2/r1. the dc output (v cc /2) is fixed by an aux- iliary amplifier common to all the channels). by controlling the amount of this local feedback it is possible to force the loop gain (a * b ) to less than unity at frequency for which the phase shift is 180 deg. this means that the output buffer is intrinsically stable and not prone to oscillation. most remarkably, the above feature has been achieved in spite of the very low closed loop gain of the amplifier. in contrast, with the classical pnp-npn stage, the solution adopted for reducing the gain at high frequencies makes use of external rc networks, namely the boucherot cells. other outstanding characteristics: clipping detector output the TDA7374B is equipped with an internal cir- cuit able to detect the output stage saturation pro- viding a proper current sinking into a open collec- tor output (pin 10) when a certain distortion level is reached at each output. this particular function allows gain compression facility whenever the amplifier is overdriven, thus obtaining high quality sound at all listening levels. figure 13: the new output stage figure 14: clipping detection waveforms TDA7374B 7/13
offset control the quiescent output voltage must be as close as possible to its nominal value, so that less undis- torted power would be available. for this reason an input bias current compensa- tion is implemented to riduce the voltage drop across the input resistors, which appears ampli- fied at the outputs. gain internally fixed to 26db advantages of this design choice are in terms of: components and space saving output noise, supply voltage rejection and dis- tortion optimization. silent turn on/off and muting/stand-by func- tion the stand-by can be easily activated by means of a cmos level applied to pin 7 through a rc filter. under stand-by condition the device is turned off completely (supply current= 1 m a typ ; output at- tenuation= 90 db typ). every on/off operation is virtually pop free. furthermore, at turn-on the device stays in muting condition for a time determined by the v alue as- signed to the svr capacitor (t= csvr * 7,000). while in muting the device outputs becomes in- sensitive to any kinds of signal that may be pre- sent at the input terminals. in other words every transient coming from previous stages produces no unpleasant acoustic effect to the speakers. another situation under which the device is totally muted is whenever the supply voltage drops lower than 7v. this is helpful to pop suppression during the turn-off by battery switch. built-in protection systems full protection of device and loudspeakers against ac/dc short circuits (to gnd, to vs, across the speakers) . reliable and safe operation in presence of all kinds of short circuit involving the outputs is as- sured by a built-in protection system that operates in the following way: in case of overload, a scr is activated as soon as the current flowing through the output transis- tors overcomes a preset threshold value depend- ing on the chip temperature. the scr causes an interruption of the supply current of the power transistor. load dump voltage surge the tda 7374 has a circuit which enables it to withstand a voltage pulse train on pins 3 and 13, of the type shown in fig. 16. if the supply voltage peaks to more than 50v, then an lc filter must be inserted between the supply and pins 3 and 13, in order to assure that the pulses at pins 3 and 13 will be held within the limits shown. a suggested lc network is shown in fig. 15. with this network, a train of pulses with amplitude up to 120v and width of 2ms can be applied at point a. this type of protection is on when the supply voltage (pulse or dc) exceeds 18v. for this reason the maximum operating supply volt- age is 18v. polarity inversion high current (up to 10a) can be handled by the device with no damage for a longer period than the blow-out time of a quick 2a fuse (normally connected in series with the supply). this fea- tures is added to avoid destruction, if during fitting to the car, a mistake on the connection of the supply is made. open ground when the radio is in the on condition and the ground is accidentally opened, a standard audio amplifier will be damaged. on the TDA7374B pro- tection diodes are included to avoid any damage. inductive load a protection diode is provided to allow use of the TDA7374B with inductive loads. figure 15 figure 16 TDA7374B 8/13
dc voltage the maximum operating dc voltage for the TDA7374B is 18v. however the device can withstand a dc voltage up to 28v with no damage. this could occur dur- ing winter if two batteries are series connected to crank the engine. thermal shut-down the presence of a thermal limiting circuit offers the following advantages: 1)an overload on the output (even if it is perma- nent), or an excessive ambient temperature can be easily withstood. 2)the heatsink can have a smaller factor of safety compared with that of a conventional circuit. there is no device damage in case of excessive junction temperature: all happens is that p o (and therefore p tot ) and i d are re- duced. the maximum allowable power dissipation de- pends upon the size of the external heatsink (i.e. its thermal resistance); fig. 17 shows the dissi- pable power as a function of ambient temperature for different thermal resistance. loudspeaker prot ection the TDA7374B guarantees safe operations even for the loudspeaker in case of accidental shortcir- cuit. whenever a single out to gnd, out to v s short circuit occurs both the outputs are switched off so limiting dangerous dc current flowing through the loudspeaker. figure 17: maximum allowable power dissipation vs. ambient temperature TDA7374B 9/13
clipping detector fig 19 shows an application using the TDA7374B in combination with the sgs-thomson audio- processor tda7302. the output clipping is recognized by the microproc- essor (in this application it is simulated by a pc). the detailed way to operate of the system is rep- resented by the flow-chart of fig.18. the controller detects when the clipping is active (minimun detection width fixed by a c29 = 12 nf external capacitor), and reduces the volume (or bass ) by step of 2 db (with a programmable wait- ing time), until no more clipping is detected. then the controller waits for a programmable time before increasing the volume again by s tep of 2 db until clipping is again detected or the panel se- lected volume is reached. practical advantages of this application is a better sound quality deriving from operation under no clipping conditions, which also means the avail- ability of higher undis torted power. what is needed for a demonstration - a xt or at ibm compatible pc, supplied with ega card - a sgs-thomson audioprocessor application disk - a tda 7302 + TDA7374B board - a connector from audioprocessor board to pc parallel port general information in the application shown in fig 18 the tda7302 audioprocessor works on pc xt or at ibm com- patible. control is accomplished by serial bus ( s-bus or i 2 c-bus or spi bus) sent to the test board through the pc parallel port. the pc simulates the behaviour of the microproc- essor in a real application (for example in a car radio) and the buffer is necessary only in this ap- plication for protecting the pc. figure: 18: clipping detector control routine TDA7374B 10/13
figure 19: application with tda7302 + TDA7374B TDA7374B TDA7374B 11/13
multiwatt15 (vertical) package mechanical data 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 1.02 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 TDA7374B 12/13
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 publi cation are subject to change without not ice. this publication sup ersedes and replaces all information previously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in life support dev ices or systems without ex- press written approval of sgs-thomson microelectronics. ? 1995 sgs-thomson microelectronics - all rights reserved sgs-thomson microelectronics group of companies aust ralia - brazil - france - germany - hong kong - italy - japan - korea - malaysia - malta - morocco - the netherlands - singapore - spain - sweden - switzerland - taiwan - thaliand - united k ingdom - u.s.a. TDA7374B 13/13

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