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TAS5805M: Audio AMP TAS5805M PVDD power question.

Tony Wu
Prodigy 40 points
Part Number: TAS5805M


Tool/software:

Hi,

I am designing Speaker function. And we will use TAS5805M ampilifer chip.

We will design two 5W/4ohm speakers. and consider how PVDD voltage suitable.

1.Can I use PVDD=5V or need to use 12 or 24V ?

If need 12V, I need add DC/DC boost IC, let input 5V become 12V/24V.

2.How the Boost IC current need if speakers is 5W*2? May I know how to caculate PVDD current ?

Thanks

  • 0 in reply to Jesse Ji
    Prodigy 40 points

    Hi Jesse,

    Thank for your explanation, it's very clear.

    So, if our speakers are 5W/4 ohm *2, PVDD should use 7.18V at least.

    But, if I use 12V to PVDD power. does it mean DCDC IC current output can use lesser than 3.06A? Due to power from 7.18V change to 12V, that it I think.

    And, could you please recommend TI DCDC boost IC part number for this case? 

    Thanks

  • +1
    TI__Mastermind 20541 points

    hi tony

    base on your condition, 5v is not enough for generating 2x5w.

    5w/4ohm, the Vrms is sqrt(5*4) = 4.47v.

    Vpeak = 1.414*Vrms = 6.32v.

    so at least you need 6.32v pvdd.

    considering rdson and inductor loss, the current flow through speaker is around Ipk = sqrt(5/4)*1.414= 1.58A.

    as you have 2speakers, the current should be double, then around 2*1.58 = 3.06A need to be provided form pvdd.

    rdson is 0.18ohm. 

    let us assume dcr is 0.1ohm.

    then the voltage drop is around = 3.06*(0.18+0.1)= 0.86v.

    so pvdd need at least 6.32+0.86 = 7.18v. 

    the current at least need 3.06A from boost.

    keep 1.5 times margin should be better.

    thanks

    jesse

  • 0 in reply to Tony Wu
    TI__Mastermind 20541 points

    hi Tonly

    if the current is less than 3.06A, the voltage will drop a lot if current be extracted too much.

    about the DCDC part, submit a new ticket will be better.

    thx

    jesse