8.5.3 Calculating SOA Adjustments

• SOA adjustment for switching frequency ≈ -0.2°C (Figure 6)
• SOA adjustment for input voltage ≈ 2.5°C (Figure 7)
• SOA adjustment for output voltage ≈ 1°C (Figure 8)
• SOA adjustment for output inductor ≈ 2.3°C (Figure 9)
• Final calculated SOA adjustment = -0.2 + 2.5 + (-1.5) + 2.3 ≈ 3.1°C

VIN = 12 V

VDD = 5 V

VOUT = 1.8 V

ƒSW = 500 kHz

LOUT = 0.29 µH

Figure 16. Power Stage CSD97376Q4M SOA

In the design example above, the estimated power loss of the CSD97376Q4M would increase to 2.3 W. In addition, the maximum allowable board and/or ambient temperature would have to decrease by 3.1°C. Figure 16 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 3.1°C. In the event the adjustment value is a negative number, subtracting the negative number would yield an increase in allowable board/ambient temperature.