SLPS598C May 2017 – January 2018 CSD88584Q5DC
If the case and board temperature of the power block are known, the SOA can be used to determine the maximum allowed current that will maintain operation within the safe operating area of the device. The following procedure outlines how to determine the RMS current limit while maintaining operation within the confines of the SOA, assuming the temperatures of the top of the package and PCB directly underneath the part are known.
In the example below, we show how to achieve this for the temperatures TC = 124°C and TB = 120°C. First we draw from 50 A on the Y-axis at 124°C to 120°C on the X-axis. Then, we draw a line up from where this line crosses the TX line to see that this line intercepts the SOA at 39 A. Thus we can assume if we are measuring a PCB temperature of 124°C, and a top case temperature of 120°C, the power block can handle 39-A RMS, at the normalized conditions. At conditions that differ from those in Figure 1, the user may be required to make an SOA temperature adjustment on the TX line, as shown in the next section.