BQ500101 Datasheet, PDF (12/20 Pages) Texas Instruments – NexFET Power Stage

bq500101
SLPS585 – MARCH 2016
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System Example (continued)
8.3.3.1 Calculating Power Loss and SOA
The user can estimate product loss and SOA boundaries by arithmetic means (see the Design Example below).
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.
8.3.3.1.1 Design Example
Operating Conditions: Output Current (l_SW) = 9 A, Input Voltage (V_IN ) = 8 V, Switching Frequency (ƒ_SW) = 300
kHz, Output Inductor (L_SW) = 5 µH, Duty Cycle = 50%.
8.3.3.1.2 Calculating Power Loss
• Typical Power Loss at 9 A = 1.78 W (Figure 3)
• Normalized Power Loss for switching frequency ≈ 1.03 (Figure 7)
• Normalized Power Loss for input voltage ≈ 0.96 (Figure 8)
• Normalized Power Loss for output inductor ≈ 1.075 (Figure 9)
• Final calculated Power Loss = 1.78 W × 1.03 × 0.96 × 1.075 ≈ 1.89 W
8.3.3.1.3 Calculating SOA Adjustments
• SOA adjustment for switching frequency ≈ 0.20°C (Figure 7)
• SOA adjustment for input voltage ≈ –0.30°C (Figure 8)
• SOA adjustment for output inductor ≈ 0.60°C (Figure 9)
• Final calculated SOA adjustment = 0.2 + (–0.3) + 0.6 ≈ 0.5°C
Figure 11. Power Stage bq500101 SOA, T_A = 25°C
In the design example above, the estimated power loss of the bq500101 would increase to 1.89 W. In addition,
the maximum allowable board and/or ambient temperature would have to decrease by 0.5°C. Figure 11
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 0.5°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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