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Question asked by rane.aditya on Mar 10, 2016
ST L78M24 DPAK (PFA Datasheet) has input voltage max of 40V, we are operating the part at about 39V which is very close this upper limit. Our average circuit current consumption can go upto 66mA.
Actual Power Dissipation = (Vin - Vout) * Iout = (39 - 24) * 66mA = 0.99W

Max Junction Temp (Tj) = Temp Ambient (Ta) + (Power Dissipation Pd * Thermal Resistance Junction-Ambient θja)
Tj = 70 °C + (0.99W * 100 °C/W) = 169 °C

Actual Device Pd = (Tj - Ta)/θja = (125 - 70)/100 = 0.55W

Considering these parameters, below are some of our queries,
1. What will be effect on the part life w.r.t the stress its going through?
2. We do have some copper area on the board which acts as heatsink and i believe we should be considering that in the formula to determine the Pd, how can we consider that?
3. We are into production now, can you please suggest us some quick fix for this issue?