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5

iP2003

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.

Calculating Power Loss and SOA for Different Operating Conditions

To calculate power loss for a given set of operating conditions, the following procedure should be followed:

Determine the maximum current for each iP2003 and obtain the maximum power loss from Fig 1. Use the curves in

Figs. 3, 4, 5 and 6 to obtain normalized power loss values that match the operating conditions in the application. The

maximum power loss under the operating conditions is then the product of the power loss from Fig. 1 and the normal-

ized values.

To calculate the SOA for a given set of operating conditions, the following procedure should be followed:

Determine the maximum PCB temperature and Case temperature at the maximum operating current of each iP2003.

Obtain the SOA temperature adjustments that match the operating conditions in the application from Figs. 3, 4, 5 and

6. Then, add the sum of the SOA temperature adjustments to the Tx axis intercept in Fig 2.

The example below explains how to calculate maximum power loss and SOA.

Example:

Operating Conditions

Output Current = 40A

Input Voltage = 10V

Output Voltage = 3.3V

Sw Freq= 900kHz

Inductor = 0.2µH

Calculating Maximum Power Loss:

(Fig. 1)

Maximum power loss

(Fig. 3)

(Fig. 4)

(Fig. 5)

(Fig. 6)

120

10

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110

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0

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0

102030405060708090

100

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PCB Temperature (ºC)

Safe

Operating

Area

L=0.3uH

Case Temperature (ºC

)