8.5.3 Calculating SOA Adjustments

• SOA adjustment for switching frequency ≈ 0.3°C (Figure 5)
• SOA adjustment for input voltage ≈ 1.2°C (Figure 6)
• SOA adjustment for output voltage ≈ –1.1°C (Figure 7)
• SOA adjustment for output inductor ≈ 1.4°C (Figure 8)
• Final calculated SOA adjustment = 0.3 + 1.2 + (–1.1) + 1.4 ≈ 1.8°C

Figure 15. Power Stage CSD97374Q4M SOA

In the design example above, the estimated power loss of the CSD97374Q4M would increase to 3.1 W. In addition, the maximum allowable board and/or ambient temperature would have to decrease by 1.8°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 1.8°C. In the event the adjustment value is a negative number, subtracting the negative number would yield an increase in allowable board/ambient temperature.