During the SEL testing the device was heated to 125°C by using PID controlled heat gun (MISTRAL 6 System (120V, 2400W)). The temperature of the die was constantly monitored during testing at TAMU through an IR camera integrated into the control loop to create closed-loop temperature control. The die temperature was verified using a standalone FLIR thermal camera prior to exposure to heavy ions at KSEE.

The species used for the SEL testing was ¹⁶⁵Ho at 15MeV/nucleon and ¹⁶⁹Tm at 19.5 MeV/nucleon. For both ions an angle of incidence of 0° was used to achieve a LET_EFF of ≈75MeV·cm²/mg (for more details refer to Ion LET_EFF and Range in Silicon). The kinetic energy in the vacuum for ¹⁶⁵Ho is 2.474GeV and ¹⁶⁹Tm is 3.295GeV. Flux of approximately 4 × 10⁴ to 1 × 10⁵ ions×cm²/s and a fluence of ≈10⁷ ions/cm² per run was used. Run duration to achieve this fluence was ≈2 minutes. The 6 production and 7 pre-production devices were powered up and exposed to the heavy-ions using the maximum recommended input voltage of 14V and max programmable V_LDO voltage of 5.5V. Depending on the operational mode PVIN was either tied to VIN or VLDO, for more information refer to the test setup and procedures. No SEL events were observed during all four runs, indicating that the TPS7H502X-SP is SEL-free up to 75MeV·cm²/mg.Table 8-4 shows the SEL test conditions and results. Figure 7-1 and Figure 7-2 show a plot of the current versus time for runs #8 and 9 respectively.

Using the MFTF method described in Single-Event Effects (SEE) Confidence Interval Calculations application report and combining (or summing) the fluences of the four runs at 125°C (13 × 10⁷), the upper-bound cross-section (using a 95% confidence level) is calculated as:

σ_SEL ≤ 2.84 x 10^-8 cm²/device for LET_EFF = 75MeV·cm²/mg and T = 125°C.