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iP2001PbF
Fig 2. Safe Operating Area (SOA) vs. T
PCB
*
(*see AN-1030 for details)
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 = 5W
(Fig. 3) Normalized power loss for input voltage ≈ 0.925
(Fig. 4) Normalized power loss for output voltage ≈ 1.1
(Fig. 5) Normalized power loss for frequency ≈ 1.225
Adjusted Power Loss = 5W x 1.1 x 0.925 x 1.225 ≈ 6.23W
Adjusting for SOA Temperature:
(Fig. 2) SOA PCB Temperature = 90°C
(Fig. 3) Normalized SOA PCB Temperature for input voltage ≈ 2.6°C
(Fig. 4) Normalized SOA PCB Temperature for output voltage ≈ -3.5°C
(Fig. 5) Normalized SOA PCB Temperature for frequency ≈ -7.5°C
Adjusted SOA PCB Temperature = 90°C - 3.5°C + 2.6°C - 7.5° ≈ 81.6°C
0
2
4
6
8
10
12
14
16
18
20
22
0 102030405060708090100110120130
PCB Temperature (ºC)
Output Current (A)
Safe Operating
Area
V
IN
= 12V
V
OUT
= 1.6V
f
SW
= 500kHz
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
01234567891011121314151617181920
Output Current (A)
Power Loss (W)
V
IN
= 12V
V
OUT
= 1.6V
T
BLK
= 125°C
f
SW
= 500kHz
Maximum Typical
