4 Measuring Junction Temperature

The absolute maximum ratings table specifically states that the upper bound for junction temperature is 150°C and further states that "stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device." Consequently, knowing the junction temperature is important for verifying whether the device will survive a given set of operating conditions. As junction refers to the die encased in the device package, thereby shielded from a typical optical or physical probe, this presents a challenge. Fortunately, by characterizing one of the device ESD diodes covered in the previous section , the junction temperature can be determined for a given load current.

The method for measuring junction temperature for a given load is very similar to the method used for characterizing one of the internal ESD diodes. The key difference is that relating diode voltage to temperature with Equation 2 can now be leveraged to determine what temperature the junction experiences for a given load at a given ambient temperature. Figure 4-1 illustrates one possible test setup, in which heat generated from passing load current through the leadframe is monitored by the ESD diode forward biased from the GND to VOUT pins.

Figure 4-1 Junction Measurement Schematic