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iP2002PbF

Adjusting the Power Loss and SOA curves for different operating conditions

To make adjustments to the power loss curves in Fig. 1, multiply the normalized value obtained from the curves in Figs. 3,

4, 5 or 6 by the value indicated on the power loss curve in Fig. 1. If multiple adjustments are required, multiply all of the

normalized values together, then multiply that product by the value indicated on the power loss curve in Fig. 1. The resulting

product is the final power loss based on all factors. See example no. 1.

To make adjustments to the SOA curve in Fig. 2, determine your maximum PCB Temp & Case Temp at the maximum operating

intercept (see procedure no. 2 above) in Fig. 2. When multiple adjustments are required, add all of the temperatures

Operating Conditions for the following examples:

Output Current = 30A

Input Voltage = 10V

Output Voltage = 3.3V

Sw Freq= 900kHz

Inductor = 0.2uH

Example 1) Adjusting for Maximum Power Loss:

(Fig. 1)

Maximum power loss

(Fig. 3)

(Fig. 4)

(Fig. 5)

(Fig. 6)

Applying the Safe Operating Area (SOA) Curve

The SOA graph incorporates power loss and thermal resistance information in a way that allows one to solve for maximum

current capability in a simplified graphical manner. It incorporates the ability to solve thermal problems where heat is drawn

out through the printed circuit board and the top of the case.

Procedure

1) Draw a line from Case Temp axis at T

Temp axis at T

2) Draw a vertical line from the T

curve.

3) Draw a horizontal line from the intersection of the vertical

line with the SOA curve to the Y axis. The point at which

the horizontal line meets the y-axis is the SOA current.

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PCB Temperature (ºC)

Safe

Operating

Area

L = 0.30uH

Case Temperature (

ž8Ã

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