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TPS7A49: TPS7A49 current drift under high temp test

Leo Chow
Expert 3120 points
Part Number: TPS7A49

Hi,

i'm in midst of running some high temp test on TPS7A4901DGN with regulator step down from 12V to 9.3V.

Recently we found thermal issue on this device, my initial suspect that this issue was caused by output current consumption. The measured worst case current consumption was 152mA which exceeded the max current of 150mA. According to datasheet section 8.4 on operating modes, my device should still be functioning since it's still below the Ilim of 220mA since Iout<Ilim condition is still in place. if that's the case what will be the potential risks i may face & any recommended guidelines to follow? Thanks.

Regards,

Leo

  • 0
    TI__Genius 10200 points

    Hi Leo,

    You are correct in that the device should still function with 152 mA load current. However we do not recommend exceeding the recommended operating conditions to ensure long term functionality and reliability of the LDO. 

    As you are running tests at high temp and have 0.4 W power dissipation, the LDO could be entering thermal shutdown depending on your ambient testing temperature and PCB layout. The device's junction temperature can be calculated from the following equation:

    Tj = Ta + Rja * Pd

    Tj is the junction temperature

    Ta is the ambient temperature at which the tests are being conducted

    Pd is the power dissipation across the LDO pass FET

    Rja is the package dependent junction-to-ambient thermal resistance specified in the datasheet

    To ensure the device does not enter thermal shutdown, the junction temperature must not exceed 125 C. From this and your application's parameters, you can estimate the maximum ambient temperature that the LDO can be tested at. Keep in mind that this is only an estimate since the Rja specified in the datasheet is determined using the industry standard JEDEC High-K 4 layer thermal test board described in JESD51-7. The following application report explains how to calculate the Rja specific to your board: 

    http://www.ti.com/lit/an/slva422/slva422.pdf

    If the thermal performance of your current design is not sufficient, Rja can be reduced significantly by adding more copper to the PCB connected to the LDO. Internal power and ground planes help dissipate heat without increasing the total area of the regulator. Thermal vias around the LDO also aid in heat distribution. 

    Thanks,

    Gerard