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TPS7B82-Q1: TPS7B8250 5V output voltage decreased when Vin exceed 14V at 300mA load condition

Part Number: TPS7B82-Q1

Hello

TPS7B8250 5V output voltage decreased when Vin exceed 14V at 300mA load condition , maybe it is caused by high power dissipation.Could you give the related Vin range datas that can guarantee stabilized output 5V/300mA

  • Hi Fandy,

    With 14 V input to 5 V output at 300 mA, you were attempting to dissipate 2.7 W. As such, I agree you could definitely be running into thermal problems. If you observe Vout on a scope during thermal shutdown, you will see what appears to be a square wave as the output cycles into and out of thermal shutdown.

    While thermal performance does depend on board layout, we can use the Thermal Information table for a first pass calculation. The Thetaja for the TPS7B82-Q1 is 63.9 C/W. The maximum operating junction temperature for this LDO is 150 C. We can use the following equation to calculate the maximum input voltage for your output voltage and current for the JEDEC hi-k board (this is the board which the Thermal Information table metrics are modeled on). For this calculation I will assume that your maximum ambient temperature is 85 C; however, you can use the same equation for your own calculations.

    Tj = Ta + Rthetaja x (Vin - Vout) x Iout
    Tj - Ta = Rthetaja x (Vin - Vout) x Iout
    (Tj - Ta) / (Iout x Rthetaja) = (Vin - Vout)
    [(Tj - Ta) / (Iout x Rthetaja)] + Vout = Vin
    [(150 C - 85 C) / (63.9 C/W x 300 mA)] + 5 V = Vin
    Vin = 8.39 V

    You can improve your application layout over the JEDEC hi-k board from a thermal standpoint by maximizing the GND copper connected to the LDO. This is because the GND plane is the primary heatsink for TPS7B82-Q1.

    Very Respectfully,
    Ryan