8.3.4.3 Calculating SOA Adjustments

• SOA adjustment for switching frequency ≈ 0.3°C (Figure 8)
• SOA adjustment for input voltage ≈ –0.12°C (Figure 9)
• SOA adjustment for output voltage ≈ 0.62°C (Figure 10)
• SOA adjustment for output inductor ≈ 0.25°C (Figure 11)
• Final calculated SOA adjustment = 0.3 + (–0.12) + 0.62 + 0.25 ≈ 1.05°C

Figure 15. Power Stage CSD95377Q4M SOA

In the previous design example, the estimated power loss of the CSD95377Q4M would increase to 3.97 W. In addition, the maximum allowable board and/or ambient temperature would have to decrease by 1.05°C. Figure 15 graphically shows how the SOA curve would be adjusted accordingly.

1. Start by drawing a horizontal line from the application current to the SOA curve.
2. Draw a vertical line from the SOA curve intercept down to the board/ambient temperature.
3. Adjust the SOA board/ambient temperature by subtracting the temperature adjustment value.

In the design example, the SOA temperature adjustment yields a reduction in allowable board/ambient temperature of 1.05°C. In the event the adjustment value is a negative number, subtracting the negative number would yield an increase in allowable board and ambient temperature.