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 , TPSM82866C , TPSM8287A06 , TPSM8287A10 , 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

2 Understanding SOA Curves

Figure 2-1 shows a Safe Operating Area (SOA) curve for the same TPSM82866A power module. SOA curves show the maximum recommended temperature versus load current, as a quick aid to check if a device is thermally suitable for a given application. This particular curve uses the ambient temperature and the EVM’s RθJA value to determine the Safe Operating Area. Using these two values, combined with the power loss at each operating point, Equation 1 creates the boundary lines in the SOA curve. The top of the curve at 6 A reflects the recommended maximum output current due to the device’s rated current, while the sloped portion of the line reflects the recommended maximum output current due to the power losses, and resulting temperature rise, at that operating point. Operate below the lines to keep the device within its rated junction temperature.

Figure 2-1 Safe Operating Area (SOA) Curve

Table 2-1 shows two operating conditions for powering an SoC with an input voltage of 5 V and output voltage of 1.2 V. Figure 2-2 demonstrates that the first operating condition (red dot) is outside of the SOA curve, at the elevated ambient temperature. The second operating condition (blue dot) shows one solution to operate within the SOA curve: lower the output current.

Table 2-1 Operating Conditions Example
Operating Condition 1Operating Condition 2
Ambient temperature: 95°CAmbient temperature: 95°C
Output current: 6 AOutput current: 5 A
Not recommendedRecommended
Figure 2-2 SOA Curve Showing Different Operating Conditions

One way to reduce the output current is to reduce the processing speed of the SoC. Another solution to operate within the SOA curve would be to reduce the maximum ambient temperature or to reduce the RθJA by adding airflow to the system.