6.5.3 Calculating SOA Adjustments

• SOA adjustment for input voltage ≈ 1.0°C (Figure 5)
• SOA adjustment for output voltage ≈ 0.68°C (Figure 6)
• SOA adjustment for switching frequency ≈ 0.75°C (Figure 4)
• SOA adjustment for output inductor ≈ 0.02°C (Figure 7)
• Final calculated SOA adjustment = 1.0 + 0.68 + 0.75 + 0.02 ≈ 2.45°C

In the design example above, the estimated power loss of the CSD86336Q3D would increase to 3.85 W. In addition, the maximum allowable board and/or ambient temperature would have to decrease by 2.45°C. Figure 31 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 2.45°C. In the event the adjustment value is a negative number, subtracting the negative number would yield an increase in allowable board/ambient temperature.

Figure 31. Power Block SOA