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TAS5805M: Correct Procedure to determine Ta(max) or maximum output power

Hideki Hayashi1
Expert 8650 points
Part Number: TAS5805M


Hi team,

There are thermal equation in spra953c.pdf. It shows Tj = Tc + Ψjt * Ploss ...(1)

Tj < 160C is a over temperature threshold and Ploss is calculated as (1/efficiency  - 1 ) * Pout, so the (1) will be Tc + Ψjt * Pout * (1/efficiency  - 1 ) < 160C...(2)

Ψjt is a stable value if same circuit, 0.3 for TAS5805M. And Pout is related to efficiency by seeing efficiency curve. Also Tc is related to Ta.

If customer wants to know maximum Ta, customer should decide wanted Pout and use (2) to calculate Tc, OK, then how to convert to Ta from Tc?

On the other hand, customer can decide maximum Ta and then calculate maximum Pout. Also how to convert Tc from Ta?

What is the coefficient of relation of Tc and Ta? Besides is it correct that the design procedure written above?

Best regards,

Hideki

  • 0
    TI__Guru 51480 points

    Hi Hideki

        It's the correct procedure you are talking about. 

        The Tc and Ta are very easy to be tested, so we don't offer their relationship. Also the thermal value will change a lot according to different power dissipation conditions.

        If you are at the very beginning of the design, you don't have anything to test. You can try to use Ψjb to calculate the junction to board temperature. And you can doing some thermal simulation to get what is the PCB board temperature under different ambient temperature.