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iP2001

Fig 2. Safe Operating Area (SOA) vs. T

(

Fig 1. Power Loss vs. Current

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.

To make adjustments to the SOA curve in Fig. 2, determine the maximum allowed PCB temperature in Fig. 2 at the required

operating current. Then, add the correction temperature from the normalized curves in Figs. 3, 4, 5 or 6 to find the final

maximum allowable PCB temperature. When multiple adjustments are required, add all of the temperatures together, then

add the sum to the PCB temperature indicated on the SOA graph to determine the final maximum allowable PCB temperature

based on all factors.

Operating Conditions for the examples below:

Output Current = 20A

Input Voltage = 7V

Output Voltage = 2.5V

Sw Freq= 750kHz

Adjusting for Maximum Power Loss:

(Fig. 1)

Maximum power loss

(Fig. 3)

Normalized power loss for input voltage

(Fig. 4)

Normalized power loss for output voltage

(Fig. 5)

Normalized power loss for frequency

Adjusted Power Loss = 5W x 1.1 x 0.925 x 1.225

Adjusting for SOA Temperature:

(Fig. 2)

SOA PCB Temperature = 90°C

(Fig. 3)

Normalized SOA PCB Temperature for input voltage

(Fig. 4)

Normalized SOA PCB Temperature for output voltage

(Fig. 5)

Normalized SOA PCB Temperature for frequency

Adjusted SOA PCB Temperature = 90°C - 3.5°C + 2.6°C - 7.5°

0

2

4

6

8

10

12

14

16

18

20

22

0

10

2030

4050

6070

8090

100

110

120

130

PCB Temperature (ºC)

Safe Operating

Area

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0

1

2

3

4

5678

9

10

11

12

13

14

15

16

17

18

19

20

Output Current (A)

Maximum

Typical