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CSD97374Q4M

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SLPS382D – JANUARY 2013 – REVISED AUGUST 2016

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Normalized Curves (continued)

Figure 14. Power Loss Test Circuit

8.5 Calculating Power Loss and SOA

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

the power loss and SOA curves in this data sheet 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.

8.5.1 Design Example

Operating conditions: output current (lOUT) = 15 A, input voltage (VIN ) = 7 V, output voltage (VOUT) = 1.5 V,

switching frequency (ƒSW) = 800 kHz, output inductor (LOUT) = 0.2 µH

8.5.2 Calculating Power Loss

•

Typical power loss at 15 A = 2.8 W (Figure 1)

•

Normalized power loss for switching frequency

≈ 1.02 (Figure 5)

•

Normalized power loss for input voltage

≈ 1.07 (Figure 6)

•

Normalized power loss for output voltage

≈ 0.94 (Figure 7)

•

Normalized power loss for output inductor

≈ 1.08 (Figure 8)

•

Final calculated power loss = 2.8 W × 1.02 × 1.07 × 0.94 × 1.08

≈ 3.1 W

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