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TPS7A1633 Overheats

Stephen Vick
Intellectual 380 points
Other Parts Discussed in Thread: TPS7A16

I'm using the TPS7A1633DGNR part (8MSOP package) to provide 3.3V in an electric vehicle design where the input can go as high as 60V.  The product utilizes a number of LEDs, so the current load can be as high as around 60ma.  This is still well below the max for the part of 100ma.

I begin experiencing overheating issues when the input voltage goes as high as 40V.  The part begins to cycle on and off and the part gets hot to the touch.  It seems to me that the layout provides adequate heatsink copper on the top layer and the grounding is also adequate.

Questions:

1) Can you tell me why the part is getting hot? 

2) Would I be better off or worse off using the 8SON part instead?

I have attached layout and schematic pics.

Thanks.  Steve

  • 0
    TI__Guru 55940 points
    Hi Stephen,

    It sounds like you are triggering thermal shutdown. Please note that when Vin is 40 V, you will be dissipating 2.2 W in the LDO ((40 V - 3.3 V) x 60 mA). This will dissipation will cause the junction temperature of the LDO to be ~146 C higher than your ambient temperature.

    The VSON package does have lower thermal metrics as seen in the Thermal Information table of the datasheet, but even with the improved thermal metrics, you will be pushing the thermal limitation of the TPS7A16 at the higher input voltages.

    It looks like your layout is pretty tight already so you may not have room, but placing a power resistor in series before the LDO will be able to spread the heat dissipation. Alternative methods such as a DCDC in series with the LDO would increase complexity and require a board spin; however, this option would also improve your application's efficiency.

    A couple suggestions for layout that will help future boards, for TPS7A16, the primary heatsink of the LDO is the GND plane. A solid connection to the thermal pad would help pull heat out of the LDO better than the thermal relief that you have currently. You can also tie the NC and PG pins to GND in order to help increase the GND plane copper at the LDO as well.

    Very Respectfully,
    Ryan