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TAS5751M: Shutdown occurs when configured as BTL 20W/channel (40W total) - Tj is below thermal shutdown threshold

user5268318
Prodigy 130 points
Part Number: TAS5751M


Conditions: 1kHz sinewave, 20W/channel into 4 Ohm load, PVDD = 23.5V (2.2A).  Thermal design matches the EV-kit reference design.  PCB is 4 layers with continuous ground on the bottom.  Directly under the the power amp the temperature is Tb=94degC when shutdown cycle begins to occur after about 15min.  Assuming the thermal resistance is about the same as the EV-kit (1.7degC/Watt) then the junction temperature is approximately 113C.  

So I have two questions based on these conditions and analysis:

1. If the Tj is well below the thermal shutdown threshold of 150degC what other mechanism causes the TAS5751M to go into shutdown cycle?

2. Can you explain the graph in figure 5 of the datasheet "Output Power vs Supply Voltage", it appears that reducing PVDD will allow more output power is that correct and why?

3. Please provide recommendations for improved performance at 20W/channel into 4 Ohm

Thanks,

Rob

  • 0
    TI__Mastermind 19080 points

    Hi,

    1. To confirm what happens in the shutdown cycle, please read the Error Status Reg (0x02).

    2. Yes, it's correct. The higher PVDD, the lower efficiency, and the more power dissipation. These power dissipation will result in heating up of the device. The limitation here is the thermal.

    3. Judging from the figure 5 on d/s. You may consider to decrease the PVDD voltage to ~15V to have higher efficiency and generate less heat. 

    Thanks!

    Regards,

    Sam