CSD97396Q4M

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SLPS572 – DECEMBER 2015

System Example (continued)

8.3.4 Calculating Power Loss and SOA

The user can estimate product loss and SOA boundaries by arithmetic means (see the Design Example).

Though the Power Loss and SOA curves in this datasheet are taken for a specific set of test conditions, the

following procedure will outline the steps engineers should take to predict product performance for any set of

system conditions.

8.3.4.1 Design Example

Operating Conditions: Output Current (lOUT) = 20 A, Input Voltage (VIN ) = 7 V, Output Voltage (VOUT) = 2.0 V,

Switching Frequency (ƒSW) = 800 kHz, Output Inductor (LOUT) = 0.2 µH

8.3.4.2 Calculating Power Loss

•

Typical Power Loss at 20 A = 3.71 W (Figure 4)

•

Normalized Power Loss for switching frequency

≈ 1.01 (Figure 8)

•

Normalized Power Loss for input voltage

≈ 1.04 (Figure 9)

•

Normalized Power Loss for output voltage

≈ 1.04 (Figure 10)

•

Normalized Power Loss for output inductor

≈ 1.07 (Figure 11)

•

Final calculated Power Loss = 3.71 W × 1.01 × 1.04 × 1.04 × 1.07

≈ 4.34 W

8.3.4.3 Calculating SOA Adjustments

•

SOA adjustment for switching frequency

≈ 0.16°C (Figure 8)

•

SOA adjustment for input voltage

≈ 0.42°C (Figure 9)

•

SOA adjustment for output voltage

≈ 0.46°C (Figure 10)

•

SOA adjustment for output inductor

≈ 0.74°C (Figure 11)

•

Final calculated SOA adjustment = 0.16 + 0.42 + 0.46 + 0.74

≈ 1.78°C

Figure 15. Power Stage CSD97396Q4M SOA

In the design example above, the estimated power loss of the CSD97396Q4M would increase to 4.23 W. In

addition, the maximum allowable board and/or ambient temperature would have to decrease by 1.78°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 1.78°C. In the event the adjustment value is a negative number, subtracting the negative number

would yield an increase in allowable board/ambient temperature.

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