SLUAAJ1 May   2022 TPS62860 , TPS62861 , TPS62864 , TPS62866 , TPS62868 , TPS62869 , TPS62870 , TPS62870-Q1 , TPS62871 , TPS62871-Q1 , TPS62872 , TPS62872-Q1 , TPS62873 , TPS62873-Q1 , TPS62874-Q1 , TPS62875-Q1 , TPS62876-Q1 , TPS62877-Q1 , TPSM82810 , TPSM82813 , TPSM82816 , TPSM82864A , TPSM82866A , TPSM8287A06 , TPSM8287A12 , TPSM8287A15

 

  1.   Trademarks
  2. 1Understanding Different Thermal Metrics
  3. 2Understanding SOA Curves
  4. 3How to Create the SOA Curve
  5. 4Designing for Optimal Thermal Performance
  6. 5Summary

3 How to Create the SOA Curve

The SOA curves are usually created from measured efficiency data on the EVM. From Equation 1, the power loss at various ambient temperatures creates the temperature rise required to reach the power module’s maximum operating temperature of 125°C.

Equation 4 calculates the power loss from the data sheet’s efficiency curves:

Equation 4. Power Loss= (Vout * Iout)*(1/η - 1) 

Because efficiency at high loads decreases with increasing temperature, the efficiency values at an elevated temperature (such as 85°C) are used. As an example, Figure 3-1 shows the efficiency curve at 85°C for the same 5 Vin and 1.2 Vout condition. At 5.5 A load with nearly 84% efficiency, Equation 4 calculates the power loss as 1.25 W. Multiplying by the 25.4 °C/W RθJA value gives a temperature rise of 32°C. Subtracting this from the 125°C maximum temperature results in a maximum ambient temperature of 93°C. Thus, the SOA curve in Figure 2-1 crosses 5.5 A near 93°C.

Figure 3-1 Efficiency at Vin = 5 V and TA = 85°C