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AN10327 tda856x and tda8571j power amplifiers rev. 01.00 ? 15 october 2004 application note document information info content keywords automotive, audio, power amplifier, st ereo, quad, btl, class ab, bipolar abstract this document contains application information for the power amplifier tda856x series and the tda8571j
philips semiconductors AN10327 tda856 x ,tda857 1j re v i s i on his t ory re v date de sc ription 1 . 0 2 0 0 41 0 1 5 f i r s t v e r s i o n contact information for ad ditional information, plea se visit: http://www.se micon d u c tors.philips. com sales.addresses@ www. semiconductors.philips. com for sale s office ad dre s se s, please sen d an email to: < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 2 of 19
philips semiconductors AN10327 tda856 x ,tda857 1j 1. introduct i on 1.1 amplifier overview this do cu me nt describ es t he appli c atio n spe c ific sub j ects of the fo llowing audio power amplifiers : tda856x famil y and tda85 71j. these amplifi e rs, which are made in a b i polar p r o c e s s, are mai n ly use d in auto m otive appli c ation s such a s car ra dios, bo oste rs and multim edia ap plicati ons. th e differen c e s betwe en the types are mai n ly the numb e r of output chann els, diffe rent load valu es an d output po wer. the followin g matrix sho w s a n overvie w of the ment ioned am plifiers a nd their prope rties. ta ble 1 : a m plifie r o v er v i e w * ddd = dyna mic d i stortion detectio n cha nne ls gain [db] loa d [ohm] inpu ts outp ut po w e r [w] ddd* [% ] pack ag e t d a8560q 2 x bt l 40 2 2 x se 2 x 4 0 10 dbs13p t d a8562q 4 x se 20 4 4 x se 4 x 1 2 10 dbs17p t d a8563q 2 x bt l 20 2 2 x se 2 x 4 0 10 dbs13p t d a8563aq 2 x bt l 20 2 2 x se 2 x 4 0 2.2 dbs13p t d a8566q 2 x bt l 26 2 2 x diff. 2 x 40 7.5 dbs17p t d a8566t h 2 x bt l 26 2 2 x diff. 2 x 40 10 hsop20 t d a8567q 4 x bt l 26 4 4 x se 4 x 2 5 10 dbs23p t d a8568q 4 x bt l 40 4 4 x se 4 x 2 5 10 dbs23p t d a8569q 4 x bt l 26 2 4 x se 4 x 4 0 10 dbs23p t d a8571j 4 x bt l 34 4 4 x se 4 x 2 6 10 dbs23p < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 3 of 19
philips semiconductors AN10327 tda856 x ,tda857 1j 2. application information 2.1 input capacitors the amplifie rs nee d ca pa citors on the in puts to get a dc d e couplin g of the input sou r ce (pre-a mplifier stage). th e impeda nce of t he input stag e together with the input cap a cito rs, create a low fre quen cy roll -of f point. a larger input capa citor me an s a lower freque ncy roll -off point. the values that sho u ld be u s ed are m entio ned in the dat ash eet of the amplifier type. the followi ng figure sh ows the influence of t he input capa citors on the frequ en cy roll-off point for the tda85 66t h. (a) input capacitor 4 70nf (b) input capacitor 2 20nf (c) input capacitor 1 00nf fig 1 . roll-off fre q u e ncy a t diffe rent in put c a p a c itor v a lue s the low frequ ency roll -off p o int can e a sil y be calculate d : tot in in db low c z f _ 3 _ 2 1 ? ? ? = ? a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 4 of 19
philips semiconductors AN10327 tda856 x ,tda857 1j for exampl e the low fre que ncy roll -off po int for the tda8566t h, wh en usi ng 22 0 n f input cap a cito rs, e qual s : hz f db low 12 10 110 10 120 2 1 9 3 3 _ = ? ? ? ? ? = ? ? f i g 2. differen t ial inp u t stag e t d a 856 6t h furthe rmo r e i t is recomme nded to u s e i nput ca pa cito rs with a low dc le akage (f ilm cap a cito rs), since a n y dc l eakage at the inputs will re sult in a dc o ffset at the outputs. electrolytic capa citors usu a lly have a re la tively high dc le akage a nd sh ould the r efore not be used. 2.2 differentia l inputs the tda 856 6 is provid ed with differenti a l i nput circuit s . this h a s th e advantag e that disturban ce s on the input s, with relati on to groun d, are greatly elim inated. ho wever, if there? s a mism atch of the in put cap a cito rs, the comm o n mode reje ction ratio (cm r r) de creases for lo w frequen cie s , sin c e the imp edan ce of the input cap a cit o rs will increa se then . < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 5 of 19
philips semiconductors AN10327 tda856 x ,tda857 1j the next figure sho w s the cmrr of the diffe rent input capa citor co nfiguratio ns : (a) 100nf input cap a citors, unmatched (<3% ) (b) 220nf input cap a citors, unmatched (<2% ) (c) 220nf input cap a citors, matched (<0.2% ) (d) ideal input capacitors fig 3 . cmrr w i t h d i f f e r e n t input c a pa c i tors it may be clear that usin g matche d inpu t capa citors g i ve the best cmrr re sults (line c). so, in order t o take optimu m advantage of t he differen t ial inputs, the input ca pa citors sho u ld be e q ual (mat che d ) and have a l o w toleran c e. also, when a very high cmrr i s requi re d it is therefo r e b e st to use i nput cap a cito rs with a high capa citan c e. whe n only a pre - amplifie r without differential output s is available, the tda8 566 can al so be driven sin g le end ed. in this way on e of the inputs sho u ld be tie d to signal g r ound via the cap a cito r, while the oth e r input is d r i v en. since this i s a comp romi se, one must consi der that the cm rr rati o will get wo rse. 2.3 loss of ground the definition of a loss of g r oun d with a power am plifier ca n be de scrib ed a s followin g : < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 6 of 19
philips semiconductors AN10327 tda856 x ,tda857 1j the ground of the po wer suppl y (car-battery ) is connected to the output of the amplifier, instead of to the amplifier-ground, after which the amplifier is switched o n . in a pra c tical situation a lo ss of gro und c ondition coul d occur d u ri n g assembly in the factory, the car man u factu r er (oem) o r i n the ca se of an aftersale s cu stome r . the followi ng picture sho w s a loss of ground con d itio n fig 4 . los s of gro u n d 0 power amplifier vp loss of ground + vp 14.4v v1 cvp ground + input output acco rdi ng to figure 4, du rin g a log, the pea k cu rrent whi c h charge s the buffer capa citor cvp, will flow from cvp into the amplifie r ground pin and can destroy the amplifier. < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 7 of 19
philips semiconductors AN10327 tda856 x ,tda857 1j fig 5. a m plifier simplified interna l schematic q6 npn lower power d1 diode parasitic + q1 pnp vp - 0 current mirror q5 npn parasitic q4 npn vp q2 pnp q3 npn upper power output power stage one channel c vp output gnd acco rdi ng to the intern al schematic of th e am plifier, th e failure me chani sm is de scrib ed step by step. duri ng a lo ss of gro und, whe n the am plifier is turne d on : 1. the buffer ca pacito r cvp is charged a nd t he curre n t flows from cvp to the amplifie r grou nd pin vi a the para s iti c diod e d1 to groun d 2. since d1 is condu cting, th e voltage on t he coll ecto r o f the lower po wer q6 equ al s ? 0.7v (und er substrate level ) 3. this cau s e s a turn-on of a para s itic np n q5 4. the cu rrent mirro r is ?a cti v ated? and pu lls a cu rrent 5. then the up p e r po we r q3 will be turn ed on and a very large cu rren t will flow, sin c e the full vp is across it 6. this will d e st roy the upper power tra n si stor in orde r to withstan d the l og it has to be preve n ted that the uppe r power i s co ndu cting. the ro ot cau s e is the co nd uction of the par a s itic di od e d1, whi c h causes a sub s trate level of ?0.7v. to preve n t the con d u c tion of d1 it is adv iced to use a schottky dio de between e a ch of the outputs a nd gro und, a c cording to fig u re 6. (so for a 4 cha nnel b t l amplifier 8 schottky diod es are to be u s ed ) < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 8 of 19
philips semiconductors AN10327 tda856 x ,tda857 1j since the sch o ttky diode h a s a lo wer tre s hol d (0 .1 .. 0.3v) it will pre v ent a current flow throug h d1 a nd so the tu rn -on of the up per po we r. duri ng turn-on of the amplifie r, the capacitor will be c harged via the schottky diode instea d of via d1. for the schottky d2 it is recommended to use a philips type byv10-40 or a doubl e smd type bat140a. fig 6 . sc hottk y diode d1 diode parasitic output q2 pnp q4 npn 0 vp vp q6 npn lower power current mirror bat140a output power stage one channel c vp byv10-40 gnd d2 diode schottky q5 npn parasitic + q3 npn upper power - q1 pnp 2.4 critical conditions 2.4.1 stability whe n usi ng capa citors fro m the outputs to ground (emc) o ne mu st consi der tha t the tda85 6 x / tda857 1 is st able for capa citan c e s smal ler than 2.2n f and larger t han 100nf. so, when capa citors are u s e d ou tside of this range, bo uche rot filters at the outputs coul d be necessa ry. < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 9 of 19
philips semiconductors AN10327 tda856 x ,tda857 1j 2.4.2 ground loo ps grou nd loo p s are un wante d sign al path s that can o c cur d u ri ng me asu r em ents o f the power am plifier, whi c h can result in a hi gher t h d performan ce of the amplifie r. a many see n fault is after co nne cting two groun d con n e c tors of an oscillo scop e pro be : one at the sign al gro und of the inp u t of the amplif ier and on e on the gro u n d of the powe r sup p ly. the sa me co ndition hold s whe n co nne cting an audi o analyser (au d io pre c isi on). in this ca se when th e grou nd con necto r (cabl e shiel d ) is con necte d to the amplifier in pu t signal grou nd an d when the outp u t is measure d , while its gro und conn ecto r (cable shiel d ) is con n e c ted to the power su pply grou nd. the followi ng drawi ng sho w s su ch a ground lo op co ndition fig 7 . ground lo op in practi ce on e sho u ld al wa ys try various groun d co nn ection s when measuri ng t hd. ho wever, in many ca se s it is advice d to use o n ly one grou nd conn e c tion from the measuri ng de vice to the po wer a m plifier board. to che c k if a grou nd loo p is pre s e n t, measu r e the di stortion resi due on an oscillo scope together with the output sig nals of the a m p lifier. the distortio n re si due is u s u a lly a monitor o u tpu t on an audio analyser, eg. audio pre c isi on system t w o, whi c h sh ows the differen c e bet wee n the sh a pe of the origi nal wavefo rm that is put on the input of the power am plifier and the wa veform that is pr esent on th e output. (be awa r e of that the audio pre c isi on system t w o do es n o t scale this di st ortion resi due !) the disto r tion resid ue sho w s a g r ou ndl oop; the wav e form sho w s the rectified frequ e ncy of the signal th at is put on the amplifie r in puts. the foll owin g pictu r e sho w s a n example of a grou nd loo p . < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 10 of 1 9
philips semiconductors AN10327 tda856 x ,tda857 1j (a) amplifier output signal (b) distortion residue 8 . oscilloscope p i c f i g t u r e of the distortion residue 2.5 c b l a y o ut recommendations en d e sig n ing a p c b f e r e n ce v i c e , e o f ? ? ? ?
philips semiconductors AN10327 tda856 x ,tda857 1j a. good b. not goo d fig 9 . ground lo op ? ?
philips semiconductors AN10327 tda856 x ,tda857 1j c. good d. not goo d fig 1 0 . pcb lay out as can be se en in pictu r e 10c i s that the si gn al gro u nd potential o f the ground pin (7,11 ) is equ al to the potential of the sign al gro und con n e c tor of the input signal. in picture 1 0 d the potential betwe en pin 7, 11 and the sign al gro und conn ecto r is uneq ual, dep endin g on the current -flow t h rou gh the track, x+y. suppo se that , at a certain output po wer, t he current throu gh the x+y grou nd tra ck e qual s 3a , while the resi stan ce of the track x+y equal s 100m ohm, then th e voltage across x+y equal s 0.3v a nd will in cre a s e with in crea sing o u tput p o we r 2.6 heatsink calculation 2.6.1 pow e r dissi pation as an exampl e, the heatsin k for a tda 8 566q i s cal c u l ated. whe n de signi ng a heat sin k , the amount of di ssi pated power mu st b e cal c ulate d first. for on e ch an nel of a conv entional cla s s b, btl amplifier, the dissipated po we r equal s : out load out p out ply diss p r p v p p p ? ? ? ? = ? = 2 2 sup a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 13 of 1 9
philips semiconductors AN10327 tda856 x ,tda857 1j o r a s t e r e o amplifier thi s mean s : acco rdi ng a rule of thumb the followi ng c an be a s sum ed : the powe r dissipatio n of a u sic sig nal i s abo ut half of the worst ca se di ssi pation of a sine wav e sign al. this means that when : the dissip ate d power for m u si c sig nal s e qual s : 2.6.2 thermal resistance a l resi stan ce [rth] equal s ohm s law, when tempe r at ure [t] is u b s tituted fo r voltage and power [p] is substituted for curre n t : in fact, t is the temperature differen c e a c ro ss the thermal re sista n ce while p is the i s s i p a t e d po wer of the am plifier, so : f out load p diss p r v p ? ? ? ? = out p ? m out p ? ? ? ? = v v p 4 . 14 = w x p out 5 2 = ? = r w v p p music diss 5 . 10 10 4 _ = ? ? ? = 5 2 2 2 ? ? the equ ation f o r t h e t h e r m s t r = p th d t r ? = diss th p < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 14 of 1 9
philips semiconductors AN10327 tda856 x ,tda857 1j whe n loo k ing at the next drawin g it may be cle a r that the total therm a l resi stan ce i s the u m o f t h e t h ermal resi sta n ce s from the juncti on (out puts) of the a m plifier to the ambient, s while the tem peratu r e diffe ren c e is the d i fference bet wee n the jun c tion tempe r a t ure of the amplifier and the ambi ent temperature. f i g 11. t h e rmal resis t an ce o t h i s m e a n s that the equ ation ca n be extended to : whe n the value of the heat sin k is dete r mined for m u sic sign als , th e equatio n le ads to : the thermal resi stan ce fro m the junctio n to case (pa c kage ) is u s u a lly drawn like three t e reo am plifier) o r five (q uad amplifie r) thermal re si stance s , but can be tran slat ed (acco r di ng to ohm s law) to one therm a l resi stan ce, a c cordi ng to the next figure. s diss a h th h c th c j th p r r r = + + ? ? ? amb vj t t ? ) ( ) ( _ ) ( h c th c j th music diss a h th r r p r ? ? ? ? ? = amb vj t t ? ( s < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 15 of 1 9
philips semiconductors AN10327 tda856 x ,tda857 1j f i g 12. t h e rmal resis t an ce o f p ack ag e i n a l l y , w h e n : h e t h e r m a l r e s i stan ce of t he req u ired h eatsin k eq ual s : the absolute maximum jun c tion tempe r a t ure at whi c h the the ambient tempe r ature in whi c h the a m plifier is u s e d , ie. in the the dissipate d power for m u si c sig nal s the thermal resi stan ce of the am plifie r a c cordi ng to the datasheet the thermal resi stan ce of therm a l pa ste f c vj = 150 amplifier d o e s not breakdo wn (valu e me ntioned in d a tash eet) c amb = 70 t dashbo ard of a car w music diss 5 . 10 _ = p w k c j th / 3 . 1 ) ( = ? r w k h c th / 1 . 0 ) ( = ? r t t w k r a h th / 2 . 6 1 . 0 3 . 1 5 . 10 70 150 ) ( = ? ? ? = ? a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 16 of 1 9
philips semiconductors AN10327 tda856 x ,tda857 1j 3. disclaimers li fe suppor t ? these produ cts are n o t d e sig ned for u s e in l i fe suppor t appliances, dev ices, or sy stems w here malfun ction o f the s e produ cts can reasona bly be ex pected to resu lt in per sonal injury . phi lips semicondu ctor s customer s usin g or selling these pro d u c ts for u s e in su ch applica t ion s do so at their ow n risk an d agree to fully inde mnify philips semi conductor s for any damages re sulti ng from su ch appli c a t io n. right to ma ke cha nges ? p h ilip s se micondu cto r s re ser v es the righ t to make chang es in th e produ cts - includi ng circuits, sta ndar d ce lls, and/or softw a re - describe d or con t aine d he re in in order to impro v e design an d/or performan ce . w h e n th e pr oduct is in fu ll produ ction (sta tu s ? p rodu ctio n?), relev ant cha nges w ill be communi ca te d v i a a customer p r oduct/process change noti fi ca tion (cpcn). philip s s e micondu ctors a s sumes n o respon sibili ty or lia bility for the u s e of any of th ese prod u c ts, conv e y s no licen ce or ti tle u nde r any paten t, c opy right, or mask w o rk ri ght to th ese products, and makes n o re pre s enta t io ns o r w a rrantie s th at the s e produ cts are free from pa ten t , copy right, or ma sk w o rk righ t in fring e m ent, unle s s otherw i se spe c i f ied . a p pl i cati on i n formati on ? ap plica t i ons tha t are descri bed here i n for any of these pr oducts a r e for illustra tiv e purpo ses only . p h ilip s se micondu cto r s make n o re presentation or w a rranty th at su ch appli c ati o n s w ill be su itabl e for the spe c i f ied use w i thou t fur t her te st ing or m o d i fi ca tion . < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 17 of 1 9
philips semiconductors AN10327 tda856 x ,tda857 1j 4. contents 1. introd uction ......................................................... 3 1.1 amplifier ov ervie w ............................................... 3 2. a p plication in formation ...................................... 4 2.1 input capa citor s ................................................... 4 2.2 differential inputs ................................................ 5 2.3 loss of gr ound .................................................... 6 2.4 critical co nditions ................................................ 9 2.4.1 stabilit y ............................................................... 9 2.4.2 ground loop s .................................................... 10 2.5 pcb lay o ut reco mmendations ......................... 11 2.6 heatsink calc ulation .......................................... 13 2.6.1 po w e r dissi pation .............................................. 13 2.6.2 t hermal resi stance ........................................... 14 3. disclaime rs ........................................................ 17 4. contents ............................................................. 18 < 1 2 nc> ? ko ni nk lij k e phil ips e l ec tr onic s n. v. 2 004. a ll r i ghts r e s e r v ed . a p p lic atio n n o t e re v . 01.00 ? 15 oct ober 2 004 18 of 1 9
philips semiconductors AN10327 tda856 x ,tda857 1j ? koni nkl i j k e philips el ec tr oni c s n.v. 2 004 al l r i g h ts ar e r e ser v ed. r epr od ucti on i n w h ol e or i n p a r t i s pr o h i b i t e d w i thout the pr i o r w r i tten cons ent o f th e copy r i g h t ow ner . t he i n f o r m a ti o n pr es ent e d i n thi s docu me nt does not for m par t o f any q uotati o n or c ontr a c t, i s b e l i e v ed to be accur a t e and r e l i a bl e and m a y be ch ang ed w i thout n o t ice. no lia bility w i l l be accept ed by the publis her f o r any conseq ue nce o f i t s use . pu bl i c ati o n ther eo f do es no t co nv ey nor i m pl y any l i c ense und e r pate n t- or oth e r i ndus tr i a l or i n tel l e ct ual pr ope r ty r i g h ts. date of re lease: 15 october 2004 document or der number : <12nc> publ i s hed i n the nether l a nds

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