Support User Manuals

Texas Instruments TPA3008D2 Stereo Amplifier User Manual

Open as PDF

of 31

www.ti.com

C

i

IN

Z

i

Z

f

Input

Signal

f +

1

2p Z

i

C

i

(5)

INPUTCAPACITOR,C

I

f

c

+

1

2pZ

i

C

i

−3 dB

f

c

(6)

C

i

+

1

2pZ

i

f

c

(7)

PowerSupplyDecoupling,C

S

TPA3008D2

SLOS435A–MAY2004–REVISEDJULY2004

The-3-dBfrequencycanbecalculatedusingEquation5.UseTable1forZ

i

values.

Inthetypicalapplication,aninputcapacitor(C

i

)isrequiredtoallowtheamplifiertobiastheinputsignaltothe

properdclevelforoptimumoperation.Inthiscase,C

i

andtheinputimpedanceoftheamplifier(Z

i

)forma

high-passfilterwiththecornerfrequencydeterminedinEquation6.

ThevalueofC

i

isimportant,asitdirectlyaffectsthebass(low-frequency)performanceofthecircuit.Consider

theexamplewhereZ

i

is137kΩandthespecificationcallsforaflatbassresponsedownto20Hz.Equation6is

reconfiguredasEquation7.

Inthisexample,C

i

is58nF;so,onewouldlikelychooseavalueof0.1µFasthisvalueiscommonlyused.Ifthe

gainisknownandisconstant,useZ

i

fromTable1tocalculateC

i

.Afurtherconsiderationforthiscapacitoristhe

leakagepathfromtheinputsourcethroughtheinputnetwork(C

i

)andthefeedbacknetworktotheload.This

leakagecurrentcreatesadcoffsetvoltageattheinputtotheamplifierthatreducesusefulheadroom,especially

inhighgainapplications.Forthisreason,alow-leakagetantalumorceramiccapacitoristhebestchoice.When

polarizedcapacitorsareused,thepositivesideofthecapacitorshouldfacetheamplifierinputinmost

applicationsasthedclevelthereisheldat2.5V,whichislikelyhigherthanthesourcedclevel.Notethatitis

importanttoconfirmthecapacitorpolarityintheapplication.

Forthebestpopperformance,C

I

shouldbelessthanorequalto1µF.

TheTPA3008D2isahigh-performanceCMOSaudioamplifierthatrequiresadequatepowersupplydecoupling

toensurethattheoutputtotalharmonicdistortion(THD)isaslowaspossible.Powersupplydecouplingalso

preventsoscillationsforlongleadlengthsbetweentheamplifierandthespeaker.Theoptimumdecouplingis

achievedbyusingtwocapacitorsofdifferenttypesthattargetdifferenttypesofnoiseonthepowersupplyleads.

Forhigherfrequencytransients,spikes,ordigitalhashontheline,agoodlowequivalent-series-resistance(ESR)

ceramiccapacitor,typically0.1µFplacedascloseaspossibletothedeviceV

CC

leadworksbest.Forfiltering

lowerfrequencynoisesignals,alargeraluminumelectrolyticcapacitorof10µForgreaterplacedneartheaudio

poweramplifierisrecommended.The10-µFcapacitoralsoservesaslocalstoragecapacitorforsupplying

currentduringlargesignaltransientsontheamplifieroutputs.

17

previous next